This invention relates to a thermoelectric generator device, in particular a thin film thermoelectric generator device.

As a clean and self-powered source, wearable thermoelectric generator devices can locally and continuously convert thermal energy from the body into electrical energy according to Seebeck effect using thermoelectric materials. Inorganic thermoelectric thin-film deposition may be used to manufacture such devices, together with low-cost fabrication technologies, e.g. roll-to-roll.

Flexible thin-film thermoelectric generators (TEGs) may be assembled having thermoelectric legs, and thus heat flows, arranged in parallel or perpendicularly to the substrate. However, the perpendicular configuration is not practical at thin-film dimensions, since maintaining a large temperature difference across a nano thickness thermoelectric leg is very difficult, leading to a poor power output.

The parallel configuration has the drawbacks that the legs of a wearable device lie in the wrong plane to best exploit the temperature difference from a user’s skin and that the in plane architecture may result in a large internal electrical resistance that can lead to a relatively high output voltage but a small working current, such that the power output is limited. Thus, for a TEG having a parallel configuration, optimising its power density is a trade-off, inter alia, between the dimensions, spacing and number of the layers of the TEG and the fill factor (the ratio between the surface area occupied by TEG materials and the overall surface area of the device), quantifies how efficiently a TEG occupies a substrate.

It is an aim to provide an improved thermoelectric generator device.

When viewed from a first aspect, the invention provides a thermoelectric generator device comprising: a thermoelectric array, wherein the thermoelectric array comprises: at least two thermoelectric stacks; and one or more connectors, wherein each of the one or more connectors extends between a pair of the at least two thermoelectric stacks, wherein each of the one or more connectors is arranged to provide a conducting or semi-conducting electrical connection between the pair of the thermoelectric stacks; wherein each of the thermoelectric stacks comprises: at least two thermoelectric units, wherein each thermoelectric unit comprises a first layer and a second layer; wherein the first layer comprises a conducting layer or a semi-conducting layer and the second layer comprises a semi-conducting layer; and wherein the first layer and the second layer are at least partially overlapped to provide an electrical connection between the first layer and the second layer; and wherein the at least two thermoelectric units are arranged one on top of the other with an insulating layer arranged between each adjacent pair of the at least two thermoelectric units; and wherein, for each adjacent pair of the at least two thermoelectric units, the first layer or the second layer of one of the thermoelectric units of the pair of thermoelectric units is in electrical contact with the first layer or the second layer of the other thermoelectric unit of the pair of thermoelectric units.

The present invention thus provides a thermoelectric generator device for converting heat flux into electrical energy. A heat flux in the device may be provided by putting the device into contact with a heat source. The device may be incorporated into wearable products such as clothing or accessories (e.g. watches or glasses) such that the heat flux across the device is generated by proximity to or contact with the body, e.g. the radiating body heat is the heat source.

The (e.g. in-plane) thermoelectric generator device of the present invention is provided by assembling multiple thermoelectric units one on top of the other (e.g. in a stacked or layered configuration) to form a thermoelectric stack. Such a configuration helps to provide a higher electrical power output from the thermoelectric device than conventional in-plane thermoelectric generator devices that, for example, have a single layer of a thermoelectric unit. Arranging the thermoelectric units one on top of the other in a layered or stacked configuration helps to improve the electrical power output, without significantly increasing the height or thickness of the device (e.g. when the thermoelectric units are formed from thin film layers). Thus device may be particularly suitable for incorporation into wearable devices and flexible materials.

In some embodiments, the thermoelectric generator device comprises a substrate, wherein the thermoelectric array is formed on the substrate. The substrate may comprise any suitable and desired material or combination of materials. In some embodiments, the substrate comprises a glass based material or a polymer based material. In preferred embodiments the substrate comprises a flexible substrate, e.g. a flexible polymer-based material, such as polythene, polypropylene, polyimide or polyimide based polymer, polycarbonate or polycarbonate polymer, poly(chloroethene), poly(tetrafluoroethene), polyethylene terephthalate (PET), polyethylene naphthalate (PEN). In some embodiments the substrate comprises a biodegradable substrate, e.g. polyesters such as polylactic acid (PLA).

The first and/or second layer of the thermoelectric units may comprise any suitable and desired material.

The first layer comprises a metal layer or a semi-conducting layer, i.e. a layer comprising a material which is a metal or a semi-conductor. In some embodiments, the first layer may comprise a metal, e.g. copper, aluminium or gold. The first layer may comprise a metal alloy.

When the first layer comprises a semi-conductor layer, the first layer may comprise an n-type semi-conductor or a p-type semi-conductor. In some embodiments the first layer comprises an n-type semi-conductor, such as bismuth telluride (Bi2Te ₃ ). In some embodiments the first layer comprises a p-type semi-conductor, such as Sb ₂ Te ₃ and Bio.5Sb1.5Te3.

The second layer comprises a semi-conducting layer, i.e. a layer comprising a material which is a semi-conductor. The semi-conductor may comprise an n-type semi-conductor or a p-type semi-conductor. In some embodiments the second layer comprises an n-type semi-conductor, such as bismuth telluride (B^Tbb). In some embodiments the second layer comprises a p-type semi-conductor, such as In some embodiments, when the first layer comprises a semi-conducting material, the second layer preferably comprises a semi-conducting layer of a different doping type. For example, if the first layer comprises an n-type semiconductor, the second layer preferably comprises a p-type semi-conductor or an undoped semi-conductor. In embodiments where the first layer comprises a metal (e.g. copper), the second layer may comprise either a p-type or n-type semiconductor.

In some embodiments, when the (e.g. in-plane) thermoelectric generator device is placed in contact with a heat source, a heat flux will be generated across the device (e.g. in parallel to the plane of a substrate) and a current will flow through the device (e.g. in the opposing direction to the heat flux). In other embodiments, when the (e.g. in-plane) thermoelectric generator device is placed in contact with a heat source, a heat flux will be generated across the device (e.g. in parallel to the plane of a substrate) and a current will flow through the device (e.g. in substantially the same direction to the heat flux). It will be appreciated that the direction in which the current flows through the device is determined by the materials used for the first and second layers.

It will be appreciated that, in addition to the heat flux, the first and second layer materials may be arranged to allow current to flow in the direction out-of-plane (e.g. direction perpendicular to the substrate) such that the current flows through (e.g. down or up) the thermoelectric stack (e.g. from the top of the stack to the bottom of the stack or vice versa).

The thermoelectric stacks of the present invention comprise at least two thermoelectric units arranged to be one on top of the other. In some embodiments, the thermoelectric stacks comprise at least three, e.g. at least four, e.g. at least five thermoelectric units.

In some embodiments, the first and second layers are arranged substantially (spatially) parallel to each other and, e.g. the first and second layers are arranged to both be parallel to the substrate. In such embodiments, it will be appreciated that the current flows across the thermoelectric generator device from a first side of the thermoelectric generator device to a second side of the thermoelectric generator device in a direction substantially parallel to the surface of the layers and, e.g., the substrate. It will be appreciated that in some embodiments the current flows in a direction substantially equal and opposite to the heat flux (e.g. temperature gradient, AT) such that the heat flows from the second side (e.g. hot(ter) side) of the thermoelectric device to the first side (e.g. cold(er) side) of the thermoelectric device.

It will be appreciated that in some embodiments the current flows in a direction substantially the same as the heat flux (e.g. temperature gradient, AT) such that the heat flows from the first side (e.g. cold(er) side) of the thermoelectric device to the second side (e.g. hot(ter) side) of the thermoelectric device). As discussed below, preferably the thermoelectric stacks of the thermoelectric generator device are arranged (spatially) parallel to each other, such that the current flows across (e.g. each) stack from a first side of the stack to a second side of the stack (in a direction substantially parallel to the surface of the layers and, e.g., the substrate).

In some embodiments the first layer and second layer have substantially the same total surface area. In some embodiments, the first layer and the second layer have substantially the same cross-sectional shape in a plane parallel to the substrate.

For example, the first layer and the second layer may have any suitable and desired cross-sectional shape, e.g. a circle, an oval, a square or a rectangle. In preferred embodiments the first layer and the second layer (each) comprise at least one rectangular cross-sectional shape, e.g. having a length greater than a width.

In some embodiments the first layer and/or the second layer are continuous, e.g. the first layer and/or the second layer extends from the first side of the thermoelectric device to the second side of the thermoelectric device, to provide a continuous layer of material of substantially constant thickness.

In some embodiments, the first layer and/or the second layer are discontinuous. In some embodiments, only one of the first or second layer is discontinuous (with the other being continuous). For example, the first layer and/or the second layer may be arranged to include at least two distinct and separate areas of material within the layer. For example, the first layer and/or the second layer may comprise two distinct areas of layer material such that a void (e.g. absence) of material is provided between the two areas of the (e.g. first, e.g. second) layer.

In some embodiments, the two areas of a discontinuous (e.g. first, e.g. second) layer (as well as the absence of material between them) each comprises a rectangular cross-section, wherein the longitudinal axis of each rectangle is aligned along a common axis. In some embodiments the void area, in combination with the two discontinuous areas of the (e.g. first or second) layer (as well as the absence of material between them), forms a surface area which is substantially equal to the area of the continuous (e.g. second or first) layer arranged on top of the discontinuous layer.

In some embodiments, the width (e.g. the width of the cross-sectional shape of the layer in the parallel plane (e.g. the plane parallel to the substrate)) of the first layer and/or the second layer is between 0.1 mm and 30 mm, e.g. 0.1 mm and 20 mm, e.g. 0.1 mm and 10 mm, e.g. 0.1 mm and 5 mm, e.g. 0.5 mm and 5 mm, e.g. between 0.5 mm and 4 mm, e.g. between 1 mm and 3 mm, e.g. approximately 2 mm. In some embodiments the cross-sectional shape of the first and/or second layer comprises at least one rectangle wherein the width is the width of the at least one rectangle, the first layer and/or the second layer comprises a continuous rectangular cross-sectional shape, preferably the width of the rectangle is between 0.5 mm and 5 mm, e.g. between 0.5 mm and 4 mm, e.g. between 1 mm and 3 mm, e.g. approximately 2 mm.

In some embodiments, the length the first layer and/or second layer which comprises a continuous layer of material is between 2 mm and 50 mm, e.g. 5 mm and 50 mm, e.g. between 10 mm and 50 mm, e.g. between 13 mm and 30 mm, e.g. between 15 mm and 30 mm, e.g. between 20 mm and 30 mm, e.g. approximately 21 mm. In some embodiments the cross-sectional shape of the first and/or second layer comprises at least one rectangle wherein the width is the width of the at least one rectangle. ln some embodiments, where the first layer or the second layer comprises a continuous rectangular cross-sectional shape, preferably the length of the rectangle is between 5 mm and 50 mm, e.g. between 10 mm and 50 mm, e.g. between 13 mm and 30 mm, e.g. between 15 mm and 30 mm, e.g. between 20 mm and 30 mm, e.g. approximately 21 mm.

In some embodiments, the first layer and the second layer each have a thickness of less than 200 nm, e.g. less than 150 nm, e.g. less than 100 nm, e.g. less than 75 nm, e.g. less than 50 nm, e.g. less than 40 nm, e.g. less than 30 nm, e.g. less than 20 nm, e.g. less than 15 nm, e.g. less than 10 nm. Thus preferably the layers comprise thin-film layers.

In some embodiments, the first and second layer may have substantially the same thickness. In other embodiments, the first and second layer may have a different thickness such that the first layer has a thickness of less than 200 nm, e.g. less than 150 nm, e.g. less than 100 nm, e.g. less than 75 nm, e.g. less than 50 nm, e.g. less than 40 nm, e.g. less than 30 nm, e.g. less than 20 nm, e.g. less than 15 nm, e.g. less than 10 nm, and the second layer has a thickness of less than 200 nm, e.g. less than 150 nm, e.g. less than 100 nm, e.g. less than 75 nm, e.g. less than 50 nm, e.g. less than 40 nm, e.g. less than 30 nm, e.g. less than 20 nm, e.g. less than 15 nm, e.g. less than 10 nm.

It will be appreciated that the thickness of the layers may be changed depending on the material of the layer. For example, in some embodiments, when the first layer comprises a metal layer, the thickness of the layer should be sufficient (e.g. greater than 15 nm, e.g. greater than 20 nm) such that the first layer is sufficiently conductive across the layer. It will be appreciated that substantially very thin metal layers (e.g. less than 20 nm, e.g. less than 15 nm) see a decline in the conductive properties of the layers.

As described above, the at least two thermoelectric units are arranged one on top of the other such that the first layer of one of the thermoelectric units (e.g. within a pair of thermoelectric units) is in electrical contact with the first layer or the second layer of the other thermoelectric unit (within the pair of thermoelectric units), with an insulating layer arranged between the pair of thermoelectric units. By sandwiching an insulating layer between adjacent pairs of thermoelectric units, the thermoelectric units may be, at least partially, thermally and electrically isolated from each other. For example, it will be appreciated that without the presence of an insulating layer between a pair of thermoelectric units, the thermoelectric units may short-circuit, e.g. the current may be diverted such that parts of the thermoelectric unit (e.g. parts of the first and/or second layer) are bypassed.

In some embodiments, the insulating layer (e.g. sandwiched) between adjacent pairs of the thermoelectric unit may overlap (e.g. cover) between 75% and 100% of the first layer and/or second layer, e.g. between 80% and 90%, e.g. approximately 85%. In such embodiments, the area of the first and/or second layer which is not overlapped (e.g. covered) with the insulating layer is exposed such that it may form an electrical contact with a layer (e.g. the first and/or second layer) of an adjacent thermoelectric unit, e.g. arranged directly above or below.

In some embodiments, the insulating layer substantially fully overlaps the first layer and/or the second layer. For example, the insulating layer comprises a larger cross- sectional area that the first layer and/or second layer such that the first layer and/or second layer are substantially fully thermally and electrically isolated from each other in a direction perpendicular to the plane of the substrate. In such embodiments, adjacent thermoelectric units may be arranged to be in electrical contact by vias extending through the thermoelectric stack. In some embodiments, the insulating layer may comprise any suitable and desired material. Preferably the insulating layer is flexible, e.g. as well as thermally and electrically insulating. For example, the insulating layer may comprise a polymeric material. For example, the first insulating layer may comprise rubber, silicone rubber, fibre glass, acrylate, cellulose, polyurethane, polyisocyanurate, polythiophene, polyvinyl acetate (PVA) or polystyrene, or combinations thereof. In some embodiments, the first insulating layer may comprise a bioresorbable (e.g. biodegradable) material, e.g. a polyester based polymer such as polyvinyl acetate (PVA). It will be appreciated that the at least two (e.g. the plurality) of thermoelectric units within a thermoelectric stack may be electrically connected (e.g. in electrical contact) by any suitable and desired means or arrangement. For example, in some embodiments the at least two thermoelectric units within a stack may be electrically connected in series. In some embodiments, the at least two thermoelectric units within a stack may be electrically connected in parallel. In some embodiments the thermoelectric stacks may be connected in any suitable and desired combination of in series and in parallel configurations.

In some embodiments a pair of thermoelectric units of the at least two thermoelectric units are connected electrically in series, i.e. the thermoelectric stack comprises an in series electrical contact between the pair of thermoelectric units. In such embodiments, the first layer of one of the thermoelectric units in the pair of thermoelectric units is in electrical contact with the second layer of the other thermoelectric unit in the pair of thermoelectric units.

In some embodiments, the first layer and the second layer are arranged to be substantially one on top of the other, e.g. with substantially the same (e.g. rectangular) cross-sectional shape. In some embodiments, the (e.g. projected footprint of the) first and second layers (on top of each other, e.g. on the substrate) are substantially entirely overlapped. A pair of thermoelectric units having this configuration may thus comprise an in series electrical contact by arranging the first layer of one of the thermoelectric units of the pair of thermoelectric units to be substantially directly on top of (or directly below of) the second layer of the other thermoelectric unit of the pair of thermoelectric units such that the two layers are in direct electrical contact.

It will be appreciated that electrical connection between the first layer and the second layer is provided in regions where the first layer and the second layer are overlapped and thus in direct contact (e.g. absent any material disposed between the layers). As such, the extent of alignment (or misalignment) of the layers of the thermoelectric units one on top of the other may affect the quality of the electrical connection between the thermoelectric units as well within the thermoelectric units. Thus, in preferred embodiments, both the (first and second) layers of thermoelectric units and the thermoelectric units within the stack are substantially aligned on top of each other.

As discussed above, it will be appreciated the first and second layers of the thermoelectric units comprise a conducting layer or a semi-conducting layer capable of conducting heat and current such that both may flow through the thermoelectric stack.

By arranging an insulating layer between each adjacent pair of the at least two thermoelectric units allows at least partial electrical isolation between the thermoelectric units such that a short circuit is prevented. Preferably, the insulating layer is also (e.g. at least partially) thermal conducting such that the heat flux across the first and second layers (e.g. in a direction parallel to the substrate) is effectively translated up the thermoelectric stack such that the heat flux (e.g. temperature difference) across each thermoelectric unit is substantially the same and there is substantially no temperature difference across thermoelectric units in a plane perpendicular to the substrate.

As the power output of a thermoelectric unit is generally proportional to the magnitude of the temperature difference across said thermoelectric unit, it will be appreciated that provision of an insulating layer that has (e.g. good) thermal conducting properties ensures that the temperature difference across all thermoelectric units is effectively equal and thus helps to provide an improved device. As such, in preferably embodiments, the power output of a thermoelectric stack is approximately linearly dependent on the number of thermoelectric units comprised within the stack.

If the insulating layer is not (at least partially) thermally conducting, it would be appreciated that a (e.g. significant) thermal gradient would be established in the plane perpendicular to the substrate such that the heat flux across a thermoelectric unit vertically displaced from the substrate would have a smaller magnitude than the heat flux across the thermoelectric unit proximate to the substrate. As such, the power output of a thermoelectric stack would increase non-linearly as the number of thermoelectric units comprised within the stack increases. However, in some embodiments, the (e.g. each) thermoelectric unit further comprises a (e.g. second) insulating layer between the first layer and the second layer. In such embodiments, it will be appreciated that, similarly to the function of the insulating layer arranged between thermoelectric units, by sandwiching an insulating layer between the first layer and the second layer within the same thermoelectric unit, the two layers may be at least partially electrically isolated from each other.

In some embodiments, the (e.g. second) insulating layer (e.g. between the first and second layers within the same thermoelectric unit) may overlap (e.g. cover) between 75% and 100% (e.g. between 80% and 90%, e.g. approximately 85%) of the first layer and second layer, e.g. the first layer and second layer are substantially electrically and thermally isolated from each other across 75% to 100% (e.g. between 80% and 90%, e.g. approximately 85%) of the area of the first and second layers. In such embodiments, the areas of the first and second layers which are not overlapped (e.g. covered) with the insulating layer are exposed such that they may form an electrical contact therebetween. Thus, the first and second layers are in electrical contact when the two layers are in direct contact (e.g. areas where there is no insulating layer disposed between the first and second layer). Preferably, the at least two thermoelectric units in the thermoelectric stack have the first and second layers in direct contact in substantially the same location, e.g. on one side of the thermoelectric stack.

In some embodiments, the (e.g. second) insulating layer substantially fully separates the first layer and the second layer (e.g. there is substantially no direct contact between the first layer and the second layer). For example, the insulating layer comprises a larger cross-sectional area than the first layer and/or second layer such that the first layer and second layer are substantially fully thermally and electrically isolated from each other in a direction perpendicular to the plane of the substrate. In such embodiments, the first layer and the second layer of the thermoelectric unit may be arranged to be in electrical contact by vias extending through the thermoelectric units and/or thermoelectric stacks.

In some embodiments, the (e.g. second) insulating layer within a thermoelectric unit may comprise any suitable and desired material. Preferably the insulating layer is flexible, e.g. as well as thermally and electrically insulating. For example, the insulating layer may comprise a polymeric material. For example, the first insulating layer and/or the second insulating layer may comprise rubber, silicone rubber, fibre glass, acrylate, cellulose, polyurethane, polyisocyanurate, polythiophene, polyvinyl acetate (PVA) or polystyrene or combinations thereof. In some embodiments, the first insulating layer may comprise a bioresorbable (e.g. biodegradable) material, e.g. a polyester based polymer such as polyvinyl acetate (PVA). In some embodiments the insulating layer within the thermoelectric unit comprises the same material as the insulating layer arranged between the adjacent pair of the at least two thermoelectric units.

In some embodiments, the insulating layers between the (at least two) thermoelectric units and the insulating layers arranged within the thermoelectric units may be arranged in an alternating pattern such that the current flows through the thermoelectric stack from side to side (e.g. flowing between the first and second layers on one side of the thermoelectric stack and between thermoelectric units on the other side of the thermoelectric stack) in a plane substantially parallel to the substrate. Thus preferably the electrical contacts between the (first and second) layers within a thermoelectric unit and the electrical contacts between the layers of adjacent thermoelectric units alternate from side to side through the thermoelectric stack, e.g. the electrical contact(s) between the layers within a thermoelectric unit are on the opposite side of a thermoelectric stack to the electrical contact(s) between the layers of adjacent thermoelectric units.

In some embodiments, the first layer may comprise a metal and the second layer may comprise an n-type doped semiconductor (e.g. B^Tbb), such that the current flows from the first layer to the second layer through the thermoelectric units within the thermoelectric stack. In other embodiments, the first layer may comprise a metal and the second layer may comprise a p-type doped semiconductor, such that the current flows from the second layer to the first layer through the thermoelectric unit through the thermoelectric stack. As such, the direction that the current flows through a thermoelectric stack may be altered by changing the order in which the first layer and the second layer are deposited and/or changing the materials comprising the first layer and the second layer. It will be appreciated that the embodiments disclosed above are discussed with regard to two thermoelectric units for exemplary purposes only but that any suitable and desired number of thermoelectric units may be included within a thermoelectric stack in the same configuration described for two thermoelectric units (e.g. for each pair of thermoelectric units within the stack).

In some embodiments a pair of thermoelectric units of the at least two thermoelectric units are connected electrically in parallel, i.e. the thermoelectric stack comprises an in parallel electrical contact between the pair of thermoelectric units. In some embodiments, the first layer of one of the thermoelectric units in the pair of thermoelectric units is in electrical contact with the first layer of the other thermoelectric unit in the pair of thermoelectric units. In some embodiments, the second layer of one of the thermoelectric units in the pair of thermoelectric units is in electrical contact with the second layer of the other thermoelectric unit in the pair of thermoelectric units.

In some embodiments, the first or second layer is arranged to have a discontinuous cross-section comprising two distinct and independent areas of layer material with a void arranged between the two areas of layer material. In some embodiments, the layer comprising the discontinuous cross-section is the layer of the thermoelectric unit in a pair of thermoelectric units that is in electrical contact with the layer comprising a discontinuous cross-section in the second thermoelectric unit in a pair of thermoelectric units. In some embodiments, one of the layers in the thermoelectric unit (e.g. either the first or second layer) comprises two rectangular areas of the layer material (e.g. comprising conducting or semiconducting material) aligned along a common axis and separated by a void or space (e.g. a dash-space- dash arrangement of the layer material). In such embodiments, the other layer is continuous and substantially aligned on top of (or below) the void such that the continuous layer extends between the two (e.g. rectangular) areas of the discontinuous layer and at least partially overlaps both of the areas.

A pair of thermoelectric units, arranged one on top of the other and having this configuration, may thus have an in parallel electrical contact by arranging both parts of the first layer of one of the thermoelectric units of the pair of thermoelectric units to be substantially directly on top of (or directly below of) the (e.g. parts of the) first layer of the other thermoelectric unit in the pair of thermoelectric units. Similarly, the second layer of one of the thermoelectric units of the pair of thermoelectric units may be substantially directly on top of (or directly below) the second layer of the other thermoelectric unit of the pair of thermoelectric units.

Electrical connection between the first layer and the second layer is preferably provided in regions of direct contact between the first layer and the second layer, e.g. where the first layer and second layer are overlapped (e.g. absent any material disposed between the layers). As such, the extent of alignment (or misalignment) between two thermoelectric units one on top of the other (as well as between the layers within the thermoelectric units) may affect the quality of the electrical connection between the thermoelectric units (as well as within thermoelectric units). Thus, in some embodiments, both the (first and second) layers within the thermoelectric units, as well as the thermoelectric units within the stack, are substantially aligned along a common axis perpendicular to the substrate.

It will thus be appreciated that, in embodiments where the at least two thermoelectric units are arranged in parallel, the insulating layer helps to prevent the first and second layers of separate thermoelectric units agglomerating. Without an insulating layer, the first and second layers of separate thermoelectric units may be seen as a substantially unitary layer of material, e.g. having twice the thickness of the other layers. The insulating layer of the present invention thus helps to provide a physical barrier and improved mechanical properties of the thermoelectric stacks (e.g. reducing the occurrence of shearing of the first and second layers upon bending of the device), as well as (at least partial) thermal conduction and (at least partial) electrical isolation, between the thermoelectric units. This helps to substantially reduce the temperature gradient in the plane perpendicular to the substrate and thus improve the overall electrical power output by the device.

In such embodiments, the insulating layer arranged between a pair of thermoelectric units (e.g. having one layer that is discontinuous and one layer that is continuous) preferably entirely overlaps the layer (e.g. the first layer or the second layer) that is continuous and extends across the void formed by the discontinuous layer (e.g. the second layer or the first layer). For example, in some embodiments the insulating layer is at least the same size and shape as the continuous (e.g. first or second) layer, such that all of the continuous (e.g. first or second) layer is thermally (and electrically) isolated from the continuous (e.g. first or second) layer in the adjacent thermoelectric unit of a pair of thermoelectric units. In some embodiments the insulating layer is larger than the continuous layer in all dimensions within the plane of the layer (e.g. length and width).

In some embodiments, the insulating layer does not overlap substantially all of the discontinuous (e.g. the first or second layer) such that, by positioning a pair of thermoelectric units one on top of the other, an electrical contact is provided by the direct contact (e.g. overlap) between the discontinuous (e.g. first or second) layer of one of the thermoelectric units in the pair of thermoelectric units and the discontinuous (e.g. first or second) layer of the other thermoelectric unit in the pair of thermoelectric units.

In some embodiments, the insulating layer may overlap the substantially 100% of the thermoelectric units within the stack (e.g. both the first and second layers) such that each of the at least two thermoelectric units are substantially entirely thermally (and electrically) isolated from an adjacent thermoelectric unit in a pair of thermoelectric units. In such embodiments electrical contact between the at least two thermoelectric units may be provided by vias extending through the thermoelectric units and/or thermoelectric stacks.

Although the embodiments described thus far have been discussed with respect to a thermoelectric stack in which all the thermoelectric units are arranged to be in either an in parallel or an in series arrangement, it will be appreciated that a thermoelectric stack may comprise any suitable and desired arrangement, configuration or electrical connection of the plurality of thermoelectric units within a thermoelectric stack.

In some embodiments, at least one of the at least two thermoelectric stacks comprises at least two pairs of thermoelectric units, wherein at least one of the pairs of the thermoelectric units are arranged to be in electrical contact in parallel and at least one of the other pairs of the thermoelectric units are arranged to be in electrical contact in series. For example, a thermoelectric stack comprising at least three thermoelectric units (e.g. at least two pairs of thermoelectric units), wherein all the thermoelectric units are arranged to be sequentially one on top of the other with an insulating layer disposed between each adjacent pair of thermoelectric units, may have at least one pair of thermoelectric units that are arranged to have an in parallel electrical connection and at least one pair of thermoelectric units that are arranged to have an in series electrical connection.

In some embodiments, the thermoelectric stack comprises a plurality of thermoelectric units, wherein all of the thermoelectric units are arranged to be in electrical contact in parallel. In some embodiments, the thermoelectric stack comprises a plurality of thermoelectric units, wherein all of the thermoelectric units are arranged to be in electrical contact in series.

In some embodiments, the at least two thermoelectric stacks within the thermoelectric array may have the same configuration and/or arrangement of thermoelectric units. For example, the at least two thermoelectric stacks may have the same number of thermoelectric units, arranged in the same configuration and/or comprising the same materials (e.g. for the first or second layers).

In some embodiments, the at least two thermoelectric stacks within the thermoelectric array may have different configurations and/or arrangements of thermoelectric units. For example, the at least two thermoelectric stacks may have a different number of thermoelectric units and/or the thermoelectric units may be arranged in a different configuration and/or the thermoelectric units may comprise different materials (e.g. for the first or second layers).

In some embodiments, all the thermoelectric stacks within an array may have an in series electrical connection of the thermoelectric units within each thermoelectric stack.

In some embodiments, all the thermoelectric stacks within an array may have an in parallel electrical connection of the thermoelectric units within each thermoelectric stack.

In a preferred set of embodiments, the thermoelectric stacks are positioned parallel to each other, e.g. such that the thermoelectric stacks of the array are all aligned in the same direction. Thus, in a preferred embodiment, the thermoelectric stacks (each having a substantially rectangular cross-section, owing to the rectangular shape of the units and layers) are aligned parallel to each other and spaced from each other in a direction perpendicular to the longitudinal (longest) axis of the thermoelectric stacks (and their units and layers).

By connecting the thermoelectric stacks together via one or more connectors extending between pairs of thermoelectric stacks, an array of connected thermoelectric stacks is provided. This helps to further improve the power output of the device.

The one or more connectors are arranged to provide a conducting or semi conducting electrical connection between (e.g. at least two) thermoelectric stacks. The at least two thermoelectric stacks are electrically connected in any suitable and desired way by one or more connectors. In some embodiments, the one or more connectors may be made from a material with good (e.g. electrical and/or thermal) conduction properties, e.g. a metal such as copper, aluminium or gold. The one or more connectors may have any suitable and desired configuration in order to provide the one or more connections between the at least two thermoelectric stacks.

In some embodiments the thermoelectric stack further comprises a contact layer that is arranged to overlap with the one or more connectors to provide the electrical connection (e.g. overlap) between the thermoelectric stack and the one or more connectors. For example, the thermoelectric stacks may comprise a contact layer positioned at the bottom of the stack (e.g. as the most proximate layer to the substrate) and at the top of the stack (e.g. the layer farthest from the substrate).

In some embodiments the contact layer extends out from the (e.g. footprint) off the thermoelectric units to provide an area of material that may be overlapped with the one or more connectors (e.g. to provide electrical connection) without substantially any overlap between the one or more connectors and the layers of the thermoelectric units. In some embodiments the first layer or the second layer of a thermoelectric unit may also comprise (e.g. act as) the contact layer. In some embodiments the at least two thermoelectric stacks within the thermoelectric array are connected in series. For example, the one or more connectors extends (e.g. continuously) between a (e.g. each) pair of the at least two thermoelectric stacks to provide an in series electrical connection between (e.g. each of) the (at least) two thermoelectric stacks.

As discussed above, the thermoelectric stacks are arranged such that when the thermoelectric device is in contact with a heat source, current flows through the thermoelectric stacks from one side to the other (e.g. in a direction that opposes the heat flux or a direction which is substantially the same as the heat flux), regardless of whether the thermoelectric units within the thermoelectric stack are arranged in series or in parallel. Thus, a thermoelectric stack comprises a first side and a second side such that the current is arranged to flow from the first side to the second side (and the heat is arranged to flow from the second side to the first side).

In some embodiments the one or more connectors provide an in series electrical connection between a pair of thermoelectric stacks via a conducting or semi conducting electrical connection, which is preferably arranged to connect the second side of one of the thermoelectric stacks within the pair of thermoelectric stacks to the first side of the other of the thermoelectric stacks within the pair of thermoelectric stacks.

In some embodiments, the conducting or semi-conducting electrical connection comprises a conducting or semi-conducting layer which is arranged to at least partially overlap at least two of the thermoelectric stacks within the thermoelectric array.

In some embodiments, the one or more connectors may have any suitable and desired configuration or shape. For example, in some embodiments, the one or more connectors may have a “Z” shape configuration to provide an electrical connection between the first side of one thermoelectric stack within a pair of thermoelectric stacks and a second side of the other thermoelectric stack within a pair of thermoelectric stacks, e.g. to provide an in series connection between the pair of thermoelectric stacks. When the (at least) two thermoelectric stacks comprise thermoelectric units having the same materials for the first layer and the second layer, preferably the thermoelectric stacks are connected such that the connector between the (e.g. each) pair of thermoelectric stacks extends from the top layer of one thermoelectric stack to the bottom layer of the other thermoelectric stack, e.g. the current flows in the same direction (e.g. down or up) through both thermoelectric stacks.

When the thermoelectric array comprises (at least) two thermoelectric stacks, wherein the first and second layers of the thermoelectric units in the (at least) two thermoelectric stacks are different, the thermoelectric stacks may be connected such that the connector between the (e.g. each) pair of thermoelectric stacks extends from the bottom layer of one thermoelectric stack to the bottom layer of the other thermoelectric stack, e.g. the current flows in opposite directions in the two thermoelectric stacks, the current flowing down through one thermoelectric stack and up through the other.

In some embodiments the at least two thermoelectric stacks within the thermoelectric array are connected in parallel. For example, the one or more connectors extends between a (e.g. each) pair of the at least two thermoelectric stacks to provide an in parallel electrical connection between (e.g. each of) the (at least) two thermoelectric stacks.

As discussed above, the thermoelectric stacks are arranged such that when the thermoelectric device is in contact with a heat source, current flows through the thermoelectric stacks from one side to the other (e.g. in a direction that opposes the heat flux or a direction which is substantially the same as the heat flux), regardless of whether the thermoelectric units within the thermoelectric stack are arranged in series or in parallel. Thus, a thermoelectric stack comprises a first side and a second side such that the current is arranged to flow from the first side to the second side (and the heat is arranged to flow from the second side to the first side).

In some embodiments the one or more connectors provide an in parallel electrical connection between a pair of thermoelectric stacks via a conducting or semi- conducting electrical connection. For example, a connector may be arranged to electrically connect the first sides of a pair of thermoelectric stacks within the thermoelectric array. Similarly, a different connector may be arranged to electrically connect the second sides of the pair of thermoelectric stacks within the thermoelectric array.

In some embodiments, the conducting or semi-conducting electrical connection comprises a conducting or semi-conducting layer which is arranged to at least partially overlap at least two of the thermoelectric stacks within the thermoelectric array.

In some embodiments, the one or more connectors may have any suitable and desired configuration or shape. For example, in some embodiments, the one or more connectors may comprise two parallel lines or rectangles (e.g. tram lines) wherein one of the parallel lines provides electrical connection between the first sides of the thermoelectric stacks and the other parallel line provides electrical connection between the second sides of the thermoelectric stacks.

Thus, when the at least two thermoelectric stacks comprise thermoelectric units having the same materials for the first layer and the second layer, the thermoelectric stacks are preferably connected such that one connector extends from the first side of (at least) the top layer of one thermoelectric stack to the first side of (at least) the top layer of another thermoelectric stack within a pair of thermoelectric stacks and a separate connector extends from the second side of the bottom layer of one thermoelectric stack to the second side of the bottom layer of another thermoelectric stack within a pair of thermoelectric stacks, e.g. the current flows in the same direction (e.g. down or up) through both thermoelectric stacks.

When the thermoelectric array comprises (at least) two thermoelectric stacks, wherein the first and second layers of the thermoelectric units in the (at least) two thermoelectric stacks are different, the thermoelectric stacks may be connected such that the connector between the (e.g. each) pair of thermoelectric stacks extends from the first side of the top layer of one thermoelectric stack to the first side of the bottom layer of the thermoelectric stack. Similarly, the thermoelectric stacks are preferably connected on the second side by a connector between the (e.g. each) pair of thermoelectric stacks that extends from the second side of the bottom layer of one thermoelectric stack to the second side of the bottom layer of the other thermoelectric stack.

Although the embodiments described thus far have been discussed with respect to a thermoelectric array in which all the thermoelectric units are arranged to be connected in either an in parallel or an in series arrangement, it will be appreciated that a thermoelectric stack may comprise any suitable and desired arrangement, configuration or electrical connection of the plurality of thermoelectric stacks within a thermoelectric array.

For example, a thermoelectric array comprising at least three thermoelectric stacks, wherein all the thermoelectric stacks are arranged to be adjacent to one another such that the thermoelectric units within each stack are arranged to be parallel, may have at least one pair of thermoelectric stacks that are arranged to have an in parallel electrical connection and at least one pair of thermoelectric stacks that are arranged to have an in series electrical connection.

In some embodiments, all the thermoelectric stacks within a thermoelectric array have an in series arrangement of the thermoelectric stacks. In some embodiments, all thermoelectric stacks within a thermoelectric array have an in parallel arrangement of the thermoelectric stacks.

The thermoelectric generator device may be manufactured using any suitable and desired technique. Preferably the thermoelectric generator device is manufactured by depositing the components (layers and connectors) of the (units, stacks and array of the) thermoelectric generator device sequentially, e.g. one on top of each other where appropriate.

For example, the thermoelectric generator device may be manufactured by any of the following techniques: printing, sputtering, physical vapour deposition, chemical vapour deposition, roll-to-roll printing, etc.. In some embodiments, physical masks are used during the manufacturing process to form the components (layers and connectors) of the thermoelectric generator device. ln some embodiments, the plurality of thermoelectric stacks of the array are formed substantially simultaneously. For example, in some embodiments roll-to-roll printing is used to print the same layer in each of the plurality of thermoelectric stacks at the same time. In some embodiments the thermoelectric stacks may be formed one after the other.

In some embodiments the one or more connectors may be provided (e.g. deposited) in the last step of the manufacturing method, e.g. the last layer of the thermoelectric generator device comprises the connector(s).

Certain preferred embodiments for the invention will now be described, by way of example only, with reference to the accompanying drawings in which:

Figure 1A shows an expanded schematic representation of two thermoelectric units connected in series within a thermoelectric stack according to an embodiment of the present invention;

Figure 1B shows a thermoelectric unit according to an embodiment of the present invention;

Figure 2A shows an expanded schematic representation of two thermoelectric units connected in parallel within a thermoelectric stack according to an embodiment of the present invention;

Figure 2B shows a thermoelectric unit according to an embodiment of the present invention;

Figures 3A to 3C shows a series of mask designs used to manufacture a thermoelectric unit in accordance with the embodiment of the present invention shown in Figure 2B;

Figures 4A to 4F shows a series of mask designs used to manufacture a thermoelectric unit in accordance with the embodiment of the present invention shown in Figure 1B;

Figure 5A shows schematic representation of the thermoelectric stack comprising a plurality of thermoelectric units arranged to be connected in series;

Figure 5B shows a mask design for an in parallel connector that extends between at least two thermoelectric stacks in accordance with an embodiment of the present invention; Figure 5C shows a schematic representation of a thermoelectric device comprising four thermoelectric stacks as shown in Figure 5A connected in parallel by connectors of the design shown in Figure 5B;

Figure 5D shows a mask design for an in series connector that extends between at least two thermoelectric stacks in accordance with an embodiment of the present invention;

Figure 5E shows a schematic representation of a thermoelectric device comprising four thermoelectric stacks as shown in Figure 5A connected in parallel by connectors of the design shown in Figure 5D;

Figure 6A shows schematic representation of the thermoelectric stack comprising a plurality of thermoelectric units arranged to be connected in parallel;

Figure 6B shows a mask design for an in parallel connector that extends between at least two thermoelectric stacks in accordance with an embodiment of the present invention;

Figure 6C shows a schematic representation of a thermoelectric device comprising four thermoelectric stacks as shown in Figure 6A connected in parallel by connectors of the design shown in Figure 6B;

Figure 6D shows a mask design for an in series connector that extends between at least two thermoelectric stacks in accordance with an embodiment of the present invention;

Figure 6E shows a schematic representation of a thermoelectric device comprising four thermoelectric stacks as shown in Figure 6A connected in parallel by connectors of the design shown in Figure 6D;

Figure 7 shows a schematic representation of a thermoelectric stack comprising a plurality of thermoelectric units wherein some of the thermoelectric units are arranged to be connected in series and the rest of the thermoelectric units are arranged to be connected in parallel;

Figure 8 shows a schematic representation of a thermoelectric device comprising two pairs of thermoelectric stacks wherein one pair of thermoelectric stacks is connected in series and one pair is connected in parallel; and

Figure 9 shows a schematic representation of the thermoelectric device of the present invention incorporated into an electric circuit. Embodiments of the present invention will now be described that provide the components of the improved thermoelectric generator device, which converts heat flux into electrical energy.

Figure 1A shows an expanded schematic cross-sectional view of a thermoelectric stack according to an embodiment of the present invention. The thermoelectric stack 101 is formed from two thermoelectric units 100, 110 and shown in a plane perpendicular to a substrate (not shown) and parallel to the heat flux when the thermoelectric units are in contact with a heat source. The thermoelectric units 100, 110 are shown to be connected in series.

Each thermoelectric unit 100, 110 has a first layer 102 and a second layer 104 with an insulating layer 106 arranged between the first layer 102 and second layer 104. As can be seen in Figure 1A, the first layer 102 and the second layer 104 are aligned such that they are substantially one on top of the other with the insulating layer 106 being offset horizontally from the first layer 102 and second layer 104.

The horizontal offset of the insulating layer 106 provides a region 112 within the thermoelectric unit 100, 110 where the first layer 102 and the second layer 104 are in direct and thus electrical contact.

As shown in Figure 1A, the thermoelectric units 100, 110 are arranged to be substantially one on top of the other with an insulating layer 108 arranged between the two thermoelectric units 100, 110. Similarly to the insulating layer 106 within the thermoelectric units 100, 110, the insulating layer 108 between the thermoelectric units 100, 110 is offset horizontally from the first layers 102 and the second layers 104 of the thermoelectric units 100, 110. This horizontal offset of the insulating layer 108 with respect to the thermoelectric units 100, 110 provides a region 114 where there is no insulating layer 108 material between the first layer 102 of one thermoelectric unit 110 and the second layer 104 of the other thermoelectric unit 100. As such, the two thermoelectric units 100, 110 are in direct (electrical) contact at these regions 114 of overlap.

Figure 1A thus shows an embodiment where the offset of the insulating layer 108 within the thermoelectric units 100, 110 is in the opposite direction to that of the insulating layers 106 between the thermoelectric units 100, 110, such that the insulating layers 106 within the thermoelectric units 100, 110 and the insulating layers 108 between the thermoelectric units 100, 110 have an alternating horizontal offset pattern. As such, the electrical connection (at the inter-layer region 114) provided between a pair of adjacent thermoelectric units 100, 110 is arranged to be on the opposite side of a thermoelectric stack 101 than the electrical connection (at the inter-unit region 112) provided between the first layer 102 and second layer 104 within a thermoelectric unit 100, 110.

It will be appreciated that, although only two thermoelectric units 100, 110 are shown in Figure 1 A, a greater number of thermoelectric units may be provided with the same structure by reproducing the layers shown any suitable and desired number of times.

Figure 1B shows a schematic representation of a thermoelectric unit 100, 110 (e.g. comprising a first layer 102, a second layer 104 and an insulating layer 106 arranged between them) shown in Figure 1 A which shows a representation of the layers of a single thermoelectric unit 100, 110 after deposition by printing and/or sputtering techniques onto a substrate 120. In addition, Figure 1B shows a contact layer 101 arranged beneath the thermoelectric unit (e.g. the contact layer comprises at least part of the first layer deposited on the substrate 120) which extends beyond the thermoelectric unit 100, 110. The contact layer 101 provides a region of overlap (e.g. electrical contact) with the one or more connectors that extend between thermoelectric stacks (of which the thermoelectric unit 100, 110 shown is a part) of the thermoelectric array of the present invention.

For the sake of clarity, the layers in Figures 1A and 1B are shown thicker (relative to their length) than they may be in practice, such that the angle of the layers at the edges of their overlap is exaggerated.

As can be seen from Figure 1 B, the region of electrical contact 112 between the first layer 102 and the second layer 104 of the same thermoelectric units 100, 110 is formed by the deposition of one layer filling the void or spaces formed by the deposition. It will be appreciated that, although not depicted, the same will be true of the region of electrical contact 114 between two thermoelectric units 100, 110 (e.g. after the second layer 104 of a second thermoelectric unit has been deposited on top of the thermoelectric unit shown in Figure 1B).

It will be appreciated that the order of the first and second layers shown in Figure 1B are for exemplary purposes only and not intended to be limiting. Indeed, the first and second layers of the thermoelectric unit 100, 110 may be deposited in any suitable and/or desirable order. For example, the first layer 102 may be deposited such that it forms the layer proximate to the substrate 120 with the insulating layer 106 and then second layer 104 deposited thereon (e.g. in a configuration substantially reversed to that shown in Figure 1B). In preferable embodiments, the contact layer 101 will form at least part of the layer most proximate to the substrate (e.g. the layer deposited on the substrate first).

Figure 2A shows an expanded schematic cross-sectional view of a thermoelectric stack according to an embodiment of the present invention. The thermoelectric stack 201 is formed from two thermoelectric units 200, 210 in a plane perpendicular to the substrate and parallel to heat flux when the thermoelectric units are in contact with a heat source. The thermoelectric units 200, 210 are shown to be connected in parallel.

Each thermoelectric unit 200, 210 has a first layer 202 which is discontinuous comprising two areas of material 202a, 202b and a second layer 204 which is arranged to extend between the two discontinuous areas 202a, 202b such that it bridges the void formed by the first layer 202. As can be seen in Figure 2A, the first layer 202 and the second layer 204 are aligned such that they are partially overlapped at each end of the second layer 204. This arrangement provides two regions 112a, 112b of overlap between the layers within the thermoelectric units 200, 210 where the first layer 202 and the second layer 204 are in direct and thus electrical contact.

As shown in Figure 2A, the thermoelectric units 200, 210 are arranged to be substantially one on top of the other with an insulating layer 208 arranged between the two thermoelectric units 200, 210. The insulating layer 208 between the thermoelectric units 200, 210 is shown in this embodiment to have a greater length and thus surface area than the second layer 204 such that the insulating layer 208 fully overlaps the second layer 204 such that the second layer 204 is only in direct contact with the insulating layer 208 and the first layer 202 of the same thermoelectric unit 200, 202, e.g. the second layer of one thermoelectric unit 200, 202 is not in contact with any layer (either first layer 202 or second layer 204) of any adjacent thermoelectric unit 200, 202.

In the embodiment shown in Figure 2A, the insulating layer 208 does not fully overlap the first layer 202 such that two regions 214a, 214b are provided (one in each area 202a, 202b of the first layer 202) where there is no insulating layer 208 provided between the first layer 202 of one thermoelectric unit 210 and the first layer 202 of the other thermoelectric unit 200. As such, the two thermoelectric units 200, 210 are in direct (electrical) contact at these regions 214a, 214b of overlap.

It will be appreciated that, although only two thermoelectric units 200, 210 are shown in Figure 2A, a greater number of thermoelectric units may be provided with the same structure by reproducing the layers shown and suitable and desired number of times.

Figure 2B shows a schematic representation of a thermoelectric unit 200, 210 shown in Figure 2A which shows a representation of the layers after deposition by printing and/or sputtering techniques onto a substrate 220. Again, for the sake of clarity, the layers in Figures 2A and 2B are shown thicker (relative to their length) than they may be in practice, such that the angle of the layers at the edges of their overlap is exaggerated.

As can be seen from Figure 2B, the regions of electrical contact 212a, 212b between the first layer 202 and the second layer 204 of the same thermoelectric units 200, 210 is at least partially formed by the deposition of the second layer 204 filling the void or spaces formed by the deposition of the discontinuous areas 202a, 202b of the first layer 202. It will be appreciated that, although not depicted, the electrical contact 214 between two thermoelectric units 200, 210 will be formed in the void which results by the insulating layer 208 being shorter (e.g. having a smaller surface area) than the full extension length of the first layer 202. Figures 3A to 3C shows a series or sequence of mask or stencil designs 301, 303, 307 used to manufacture the thermoelectric unit 200, 210 as shown in Figures 2A and 2B. The masks 301, 303, 307 comprise areas of mask material (e.g. plastic material) as well as areas 300a, 302a, 302b, 304, 300b absent material that form the shapes and/or patterns required for the manufacturing process.

All the masks 301, 303, 307 shown in Figure 3 have two main components that form the layer pattern, the voids 302, 304, 308 having the cross-sectional shape (e.g. rectangles) that form the desired layers of the thermoelectric unit 200, 210 and the alignment dots 300a, 300b, 300c. The alignment dots 300a, 300b, 300c thus provide an alignment tool for the masks 301, 303, 307 when manufacturing the thermoelectric units 200, 210 such that when the alignment dots of the masks 301, 303, 307 are overlaid with the dots formed by the deposition of previous layers, the correct alignment is established in the thermoelectric unit 200, 210 for the layer being printed with respect to the layers that have already been deposited.

Figure 3A shows a mask 301 for manufacturing the first layer 202 of a thermoelectric unit 200, 210 for five separate thermoelectric units 200, 210 in five independent adjacent thermoelectric stacks. The first layer 202 is thus formed by positioning the mask 301 relative to the substrate and/or a previously formed thermoelectric unit (e.g. if the thermoelectric unit 200, 210 being deposited is not the first thermoelectric unit within a stack) and depositing the first layer material over the top of the mask 301 such that only the material printed over the cut away areas (e.g. areas devoid of mask material) 300a, 302a, 302b are deposited onto the substrate.

Once the first layer 202 has been deposited, the mask 301 (Figure 3A) is removed and replaced with the next mask 303 (Figure 3B) such that the alignment dots 300b are positioned directly over the top of the first layer material that was deposited through the alignment dots 300a. The second layer 304 is then deposited such that the second layer material is deposited through the voids 304 in the mask, such that the second layer material partially overlaps with both of the previously deposited areas 202a, 202b of the first layer 202 using mask 301 and fills the void between them. After the second layer 204 has been deposited, the mask 303 (Figure 3B) is removed and replaced with the next mask 307 (Figure 3C) to allow deposition of the insulating layer 208 through the void 308. Again, the alignment dots 300c are used to position mask 303 in the correct position using the material from previous layers that was deposited through the alignment dots 300a, 300b of previous masks 301, 303.

Figure 3C represents an embodiment where one insulating layer 208 may form the insulating layer 208 for a plurality of thermoelectric stacks, e.g. the insulating layer 208 formed by the void 308 in the mask 307 has one continuous area that overlaps all thermoelectric units 200, 210 that are being manufactured simultaneously (e.g. five thermoelectric units as shown in Figures 3A to 3C). However, it will be appreciated that as the insulating layer 208 provides thermal and electrical insulation between the thermoelectric units within a given thermoelectric stack, the mask 307 may be replaced with a mask comprising five distinct rectangles that are larger in size that the areas 304 of the second layer mask 303 that form the second layer 204. In this way, that at least the second layer 204 is entirely covered by insulating material when the insulating layer 208 is deposited.

It will thus be appreciated that the sequence of masks shown in Figure 3A to 3C represent the manufacture of one thermoelectric unit 200, 210 with one insulating layer 208 disposed on top (as shown in Figures 2A and 2B). By repeating the process discussed above, any suitable and desired number of thermoelectric units 200, 210 may be deposited to form a thermoelectric stack. Similarly, the number of voids provided by the mask means any suitable and desired number of adjacent thermoelectric stacks may be deposited simultaneously.

Further, it may be noted that the order in which the first layer mask 301 and second layer mask 303 are used may be switched relative to the sequence discussed above such that the second layer 204 is deposited first and then the first (discontinuous) layer 202 is deposited on top (with the insulating layer 208 on top of the first layer 202).

Similarly to Figures 3A to 3C, Figures 4A to 4F shows a series or sequence of mask or stencil designs 401, 403, 405, 407, 409, 411 used to manufacture a thermoelectric unit 100, 110 as shown in Figure 1B. As with the masks 301, 303, 307, the masks 401 , 403, 405, 407, 409, 411 shown in Figures 4A to 4F comprise areas of mask material (e.g. plastic material) as well as areas absent material 400a- f, 402, 404, 406, 408, 410, 412 that form the shapes and/or patterns required for the manufacturing process.

Figure 4B shows a mask 403 for manufacturing the second layer 104 of a thermoelectric unit 100, 110 for five separate thermoelectric units 100, 110 in five independent adjacent thermoelectric stacks. The second layer 104 is thus formed by positioning the mask 403 relative to the substrate and/or a previously formed thermoelectric unit (e.g. if the thermoelectric unit 100, 100 being deposited is not the first thermoelectric unit within a stack) and depositing the second layer material over the top of the mask 403 such that only the material printed over the cut away areas (e.g. areas devoid of mask material) 400, 402 are deposited onto the substrate.

Once the second layer 104 has been deposited, the mask 403 (Figure 4B) is removed and replaced with the next mask 407 (Figure 4C) such that the alignment dots 400c are positioned directly over the top of the first layer material that was deposited through the alignment dots 400b. The insulating layer 106 is thus deposited to at least partially overlap all of the second layers 104 for all thermoelectric units that were deposited in the previous step, for example, all of the first layers are overlapped with the insulating layer to the same extent, e.g. approximately 85%.

The first layer 102 is then deposited (by replacing the insulating layer mask 407 with the second layer mask 405) and using the first layer mask 405 (Figure 4D) such that the first layer material is deposited through the voids 404 in the mask. The first layer 102 thus overlaps with the second layer 104 in the regions where the insulating layer 106 was not deposited, as shown in Figures 1A and 1B.

After the first layer 102 has been deposited, the mask 405 is removed and replaced with the next mask 409 (Figure 4E) to allow deposition of the insulating layer 108 through the void 408. The alignment dots 400d are used to position the mask 409 in the correct position using the material from previous layers that was deposited through the alignment dots 400b, 400c, 400e of the previous masks 403, 407, 405.

It will be seen that the insulating layer masks 407, 409 shown in Figure 4C and 4E are identical and comprise two rows of alignment dots 400c and 400d. As discussed above in relation to Figure 1A, the insulating layers 106 within each thermoelectric unit 100, 110 and the insulating layers 108 between each adjacent thermoelectric unit 100, 110 have an alternating offset. This offset is achieved by alternating which alignment dots 400c, 400d are used to position the insulating layer mask 407, 409. In the embodiment shown, using the right hand column of alignment dots 400c will result in a left-shifted offset of the insulating layer deposited, whilst using the left hand column of alignment dots 400d will result in a right-shifted offset of the insulating layer.

It will thus be appreciated that the sequence of masks shown in Figure 4B to 4E represent the manufacture of one thermoelectric unit 100, 110 with one insulating layer 108 disposed on top. By repeating the process discussed above (e.g. cycling through the masks shown in Figures 4B to 4E again), any suitable and desired number of thermoelectric units 100, 110 may be deposited to form a thermoelectric stack. Similarly, the number of voids provided by the mask, means any suitable and desired number of adjacent thermoelectric stacks may be deposited simultaneously.

Further, it may be noted that the order in which the first layer mask 405 and second layer mask 403 are used may be switched relative to the sequence discussed above such that the first layer 102 is deposited first and then the second layer 104 is deposited on top (with the insulating layer 106 sandwiched in between).

Figures 4A and 4F represent masks 401, 411 used to deposit a first and last layer of a thermoelectric stack comprising a plurality of thermoelectric units 100, 110 arranged to be in series electrical contact. The layers, formed by the deposition of material through the cut away regions 410, 412, are required at the beginning and end of the thermoelectric stack to form an electrical contact with the one or more connectors that extend between at least two thermoelectric stacks in an array. In at least preferred embodiments these layers comprise a conducting layer and are in electrical contact with the first layer of a first thermoelectric unit within a thermoelectric stack and the last layer of the last thermoelectric unit of a (e.g. adjacent) thermoelectric stack.

It will be appreciated that such contact layers at the beginning and end of a thermoelectric stack only comprising thermoelectric units 200, 210 arranged in parallel (e.g. as shown in Figures 2A and 2B, such as are formed using the masks shown in Figures 3A to 3C) is not necessary. This is because the first layer can be configured to protrude such that it may inherently itself form an electrical contact with the one or more connectors. However, additional layers may be provided at the top and bottom of a thermoelectric stack if desired, regardless of the arrangement of the thermoelectric units therebetween.

In embodiments where the thermoelectric stack comprises a mixture of thermoelectric units 100, 110 in series and thermoelectric units 200, 210 in parallel, the additional contact layers at the top and bottom of the thermoelectric stack provided by the contact masks 401 , 411 may be required, to provide an electrical contact to the one more connectors.

Figure 5A shows a side cross-sectional view of a schematic representation of a thermoelectric stack according to an embodiment of the present invention. Again, for the sake of clarity, the layers in Figure 5A (and those shown in Figures 5C and 5E) are shown thicker (relative to their length) than they may be in practice, such that the geometry of the layers at the edges of their overlap is exaggerated.

The thermoelectric stack 500 comprises a plurality of thermoelectric units 100, 110 (e.g. as shown in Figures 1A and 1B) arranged to be connected in series. The thermoelectric stack 500 is formed on a polymer sheet substrate 520 with the first layer adjacent to the polymer substrate 520 being a contact layer 501 (e.g. deposited using mask 401 as shown in Figure 4A). The last layer in the thermoelectric stack 500 is another contact layer 511 (e.g. deposited using mask 411 as shown in Figure 4F). Disposed between the two contact layers 501, 511 are a plurality of thermoelectric units 100, 110 arranged to be electrically in series. The arrow 505 shows the direction of heat flux from hot to cold. The embodiment shown in Figure 5A represents a thermoelectric stack 500 where electrons flow through the thermoelectric stack in parallel to the heat flux, thus moving from the second (left hand) side of the thermoelectric stack to the first (right hand) side of the thermoelectric stack, up through the thermoelectric units 100, 110. The current / thus flows from the top of the first side of the thermoelectric stack 500 down through the thermoelectric units 100, 110 to the second side of the thermoelectric stack as shown by the arrows labelled with the current /.

However, it will be appreciated that, whether the current flows upwards through the thermoelectric stack (e.g. from the substrate 520 upwards) or downwards through the thermoelectric stack (e.g. towards the substrate 520 from the top layer) depends on the materials used in the first layer 102 and the second layer 104.

As stated above the direction that the current flows through a thermoelectric stack may be altered by changing the order in which the first layer and the second layer are deposited and/or changing the materials comprising the first layer and the second layer. As such, in some embodiments, the position of the contact layers 501 , 511 may be different to that which is depicted in Figure 5A. For example, in some embodiments, the contact layers 501 , 511 may be on the opposite side of the thermoelectric stack 500, than is depicted in Figure 5A, such that current may flow in through the bottom of the thermoelectric stack 500 on the first (right hand) side and out through the top of the thermoelectric stack on the second (left hand) side.

For example, the first contact 501 is shown in Figure 5A to be positioned at the bottom left of the stack but may alternatively be positioned at the top left of the stack or the bottom right of the stack depending on the materials and/or configuration of the thermoelectric stack. Similarly, the second contact 511 is shown in Figure 5A to be positioned at the top right of the stack but may alternatively be positioned at the top left of the stack or the bottom right of the stack depending on the materials and/or configuration of the thermoelectric stack.

In preferable embodiments, the contacts 501 , 511 are arranged to be at the top and the bottom of the thermoelectric stack with a relative position substantially diagonal to each other such that the thermoelectric stack is arranged between them. However in some embodiments, the contacts 501, 511 may be positioned at the top and bottom and on the same side (e.g. left or right) of the thermoelectric stack.

Figure 5B shows a design 515 for an in parallel connector 510 (e.g. formed using a mask) that extends between at least two thermoelectric stacks 500. The in parallel connector 510 comprises two parallel lines that are positioned relative to the thermoelectric stacks 500 such that they extend perpendicularly to the direction of the heat flux 505 across the thermoelectric stack 500, with one of the two parallel lines on either side of the thermoelectric stack and at least partially overlapping the contact layers 501 , 511 at the top and bottom of the thermoelectric stack 500. Alignment of the connectors to ensure overlap and a quality electrical contact between the connectors and the thermoelectric stacks 500 may be achieved using alignment dots 502, as was discussed in relation to the manufacture of the thermoelectric units 100, 110 within the thermoelectric stacks.

Figure 5C shows a three dimensional representation of an array 530 of four identical thermoelectric stacks 500 which are connected in parallel via connectors 510. As can be seen from the arrows depicting the current /, current flows into the thermoelectric array 530 on one side and into each of the four thermoelectric stacks 500 simultaneously via the in parallel connector 510 which is in contact with the contact layer 511 at the top of the thermoelectric stack 500. The current flows downwardly from the first side of the thermoelectric stack 500 through the thermoelectric units 100, 110 to exit the thermoelectric stack 500 at the second side. The current from all thermoelectric stacks 500 in the array 530 is then converged to exit the thermoelectric array 530 at one point via the connector 510.

Similarly, it may be envisaged that if the materials used for the first layer and the second layer result in the current flowing upwards through the thermoelectric stacks 500 of the array 530, the current will enter the stacks at the bottom of the first side and exit at the top of the second side.

Figure 5D shows a design 517 for a plurality of in series connectors 512 (e.g. formed using a mask) that extend between at least two thermoelectric stacks 500. The in series connector 512 comprises a Z-shaped connector that comprises two arms which are positioned relative to the thermoelectric stacks 500 such that they extend perpendicularly to the direction of the heat flux 505 and at least partially overlap the contact layers 501 , 511 at the top and bottom of two adjacent thermoelectric stacks 500. Alignment of the connectors to ensure overlap and a quality electrical contact between the connectors and the thermoelectric stacks 500 may be achieved using alignment dots 502, as was discussed in relation to the manufacture of the thermoelectric units 100, 110 within the thermoelectric stacks.

Figure 5E shows a three dimensional representation of an array 540 of four identical thermoelectric stacks 500a, 500b, 500c, 500d which are connected in series via connectors 512. As can be seen from the arrows depicting the current /, current flows into the thermoelectric array 540 on one side and into the first of the four thermoelectric stacks 500a in the array 540 via the contact layer 511. The current flows downwardly from the first side of the thermoelectric stack 500a through the thermoelectric units 100, 110 to exit the thermoelectric stack 500a at the bottom on the second side. The current then flows through the connector 512 from the bottom of the second side of the first thermoelectric stack 500a in the array 540 to the top of the first side of the second thermoelectric stack 500b in the array 540. The current then flows through the second thermoelectric stack 500b to the third thermoelectric stack 500c in the array 540 (and then the fourth 500d) in the same manner as described for the first thermoelectric stack 500a in the array 540. The current then flows out of the array 540 at the bottom of the second side of the last thermoelectric stack 500d in the array 540.

Similarly, it may be envisaged that if the materials used for the first layer and the second layer result in the current flowing upwards through the thermoelectric stacks 500 of the array 540, such that the current will enter each thermoelectric stack 500 in the array at the bottom of the first side and exit at the top of the second side.

Figure 6A shows a side cross-sectional view of a schematic representation of a thermoelectric stack according to an embodiment of the present invention. Again, for the sake of clarity, the layers in Figure 5A (and those shown in Figures 5C and 5E) are shown thicker (relative to their length) than they may be in practice, such that the geometry of the layers at the edges of their overlap is exaggerated. The thermoelectric stack 600 comprises a plurality of thermoelectric units 200, 210 (e.g. as shown in Figures 2A and 2B) arranged to be connected in parallel. The thermoelectric stack 600 is formed on a polymer sheet substrate 620 with the first and second layers adjacent to the polymer substrate 620 being the contact layers 601, 611 (e.g. deposited using the masks 401, 411 as shown in Figures 4A and 4E). Disposed on top of the two contact layers 601 , 611 are a plurality of thermoelectric units 200, 210 arranged to be electrically in parallel. The arrow 605 shows the direction of heat flux from hot to cold.

The embodiment shown in Figure 6A represents a thermoelectric stack 600 where electrons flow through the thermoelectric stack in parallel to the heat flux, thus moving from the second (left hand) side of the thermoelectric stack to the first (right hand) side of the thermoelectric stack. The current / thus flows from first side of the thermoelectric stack 600 through all thermoelectric units 200, 210 simultaneously and in parallel to the second side of the thermoelectric stack 600 as shown by the arrows labelled with the current /.

Similarly to Figure 5B, Figure 6B shows a design 515 for an in parallel connector 510 (e.g. formed using a mask) that extends between at least two thermoelectric stacks 600. The in parallel connector 510 comprises two parallel lines that are positioned relative to the thermoelectric stacks 600 such that they extend perpendicularly to the direction of the heat flux 505 across the thermoelectric stack 600, with one of the two parallel lines on either side of the thermoelectric stack and at least partially overlapping the contact layers 601 , 611 at the top and bottom of the thermoelectric stack 600. Alignment of the connectors to ensure overlap and a quality electrical contact between the connectors and the thermoelectric stacks 600 may be achieved using alignment dots 502, as was discussed in relation to the manufacture of the thermoelectric units 200, 210 within the thermoelectric stacks.

Figure 6C shows a three dimensional representation of an array 630 of four identical thermoelectric stacks 600 which are connected in parallel via connectors 510. As can be seen from the arrows depicting the current /, current flows into the thermoelectric array 630 on one side of the thermoelectric array 630 and into each of the four thermoelectric stacks 600 simultaneously via the in parallel connector 510 which is in contact with the contact layer 611 at the bottom of the thermoelectric stack 600. The current flows from the first side of the thermoelectric stack 600 through all thermoelectric units 200, 210 simultaneously to exit the thermoelectric stack 600 at the second side. The current from all thermoelectric stacks 600 in the array 630 is then converged to exit the thermoelectric array 630 at one point via the connector 510.

Similarly to Figure 5D, Figure 6D shows a design 517 for a plurality of in series connectors 512 (e.g. formed using a mask) that extends between at least two thermoelectric stacks 600. The in series connector 512 comprises a Z-shaped connector that comprises two arms which are positioned relative to the thermoelectric stacks 500 such that they extend perpendicularly to the direction of the heat flux 505 and at least partially overlap the contact layers 601, 611 at the top and bottom of two adjacent thermoelectric stacks 600. Alignment of the connectors to ensure overlap and a quality electrical contact between the connectors and the thermoelectric stacks 600 may be achieved using alignment dots 502, as was discussed in relation to the manufacture of the thermoelectric units 200, 210 within the thermoelectric stacks.

Figure 6E shows a three dimensional representation of an array 640 of four identical thermoelectric stacks 600a, 600b, 600c, 600d which are connected in series via connectors 512. As can be seen from the arrows depicting the current /, current flows into the thermoelectric array 640 on one side and into the first of the four thermoelectric stacks 600a in the array 640 via the contact layer 611. The current flows from the first side of the thermoelectric stack 600a to the second side of the thermoelectric stack 600a through all thermoelectric units 200, 210 simultaneously to exit the thermoelectric stack 600a at the bottom on the second side through contact 601. The current then flows through the connector 512 from the bottom of the second side of the first thermoelectric stack 600a in the array 640 to the bottom of the first side of the second thermoelectric stack 600b in the array 640. The current then flows through the second thermoelectric stack 600b to the third thermoelectric stack 600c in the array 640 (and then the fourth 600d) in the same manner as described for the first thermoelectric stack 600a in the array 640. The current then flows out of the array 640 at the bottom of the second side of the last thermoelectric stack 600d in the array 640. Figure 7 shows a schematic representation of a thermoelectric stack comprising a plurality of thermoelectric units wherein some of the thermoelectric units are arranged to be connected in series and the rest of the thermoelectric units are arranged to be connected in parallel.

Figure 7 shows a side cross-sectional view of a schematic representation of a thermoelectric stack 700 according to an embodiment of the present invention. Again, for the sake of clarity, the layers in Figure 7 are shown thicker (relative to their length) than they may be in practice, such that the geometry of the layers at the edges of their overlap is exaggerated.

The thermoelectric stack 700 comprises a plurality of thermoelectric units arranged to be connected in a combination of in series and in parallel. As shown, the thermoelectric stack 700 comprises three (e.g. a plurality) of thermoelectric units 100, 110 (e.g. as shown in Figures 1A and 1B) and four (e.g. a plurality) of thermoelectric units 200, 210 (e.g. as shown in Figures 2A and 2B) arranged to be connected in parallel. The thermoelectric stack 700 is formed on a polymer sheet substrate 720. The arrow 705 shows the direction of heat flux from hot to cold and the black arrows shown on the thermoelectric stack 700 show the direction of current / flowing through the thermoelectric stack.

The embodiment shown in Figure 7 represents a thermoelectric stack 700 where electrons flow through the thermoelectric stack in parallel to the heat flux, thus moving from the second (left hand) side of the thermoelectric stack to the first (right hand) side of the thermoelectric stack. The current / thus flows from the first contact 711 up through the first layer 102 to enter all thermoelectric units 200, 210 arranged in parallel as well as the uppermost thermoelectric unit 100, 110 arranged in series simultaneously. Current / thus flows from the second side to the first side through all parallel units whilst simultaneously flowing from the first side of the top most thermoelectric unit arranged in series down through the thermoelectric units 100, 110 connected to it in series to the second side of the thermoelectric stack 700. The current then exits the thermoelectric stack on the second side through a common output contact 701. However, as stated above with regard to the embodiments shown in Figures 5A, it will be appreciated that, whether the current flows downwards through the thermoelectric stack (e.g. towards the substrate 720 from the top layer as shown in Figure 7) or upwards through the thermoelectric units 100, 110 arranged in series (e.g. from the substrate 720 upwards) depends on the materials used in the first layer 102 and the second layer 104.

As such, in some embodiments, the position of the contact layers 501, 511 may be different to that which is depicted in Figure 7. For example, in some embodiments, the contact layers 501 , 511 may be on the opposite side of the thermoelectric stack 700, than is depicted in Figure 7, such that current may flow in through the bottom of the thermoelectric stack 700 on the first (right hand) side and out through the top most thermoelectric unit 100, 110 arranged in series of the thermoelectric stack 700 on the second (left hand) side.

Figure 8 shows a schematic representation of a thermoelectric device comprising two pairs of thermoelectric stacks wherein one pair of thermoelectric stacks is connected in series and one pair is connected in parallel.

Figure 8 shows a three dimensional representation of an array 850 of three thermoelectric stacks 500a, 500b, 600 forming two pairs 800, 810 of thermoelectric stacks wherein two of the thermoelectric stacks 500a, 500b are arranged such that all thermoelectric units comprised therein are connected in series (as shown in Figure 5A), and the third thermoelectric stack 600 is arranged such that all thermoelectric units comprised therein are connected in parallel (as shown in Figure 6A).

The first pair 800 of thermoelectric stacks are connected via an in series connector 512. As can be seen from the arrows depicting the current /, current flows into the thermoelectric array 850 on the first side and into thermoelectric stack 500a via the contact layer 511. The current flows downwardly from the first side of the thermoelectric stack 500a through the thermoelectric units 100, 110 to exit the thermoelectric stack 500a via contact layer 501 at the bottom on the second side. The current then flows through the connector 512 from the bottom of the second side of the first thermoelectric stack 500a in the array 850 to the top of the first side of the second thermoelectric stack 600 in the array 850. The current then flows into the thermoelectric stack 600 via contact layer 611 on the first side of the thermoelectric stack 600 and flows to the second side of the thermoelectric sack 600 simultaneously through all thermoelectric units 200, 210 to exit the thermoelectric stack 600 at the bottom of the thermoelectric stack 600 on the second side to exit the thermoelectric stack via contact layer 601.

The second pair 810 of thermoelectric stacks are connected via an in parallel connector 510. As can be seen from Figure 8, both the first side and the second side of the thermoelectric stacks 600, 500b forming the second pair 810 of thermoelectric stacks in the array 850 are connected by two connectors. As such, current that flows from the first thermoelectric stack 500a in the first pair 800 may, instead of flowing into the second thermoelectric stack 600 of the first pair 800 (which is also the first thermoelectric stack 600 of the second pair 810), may flow through connector 510 to the second thermoelectric stack 500b of the second pair 810. As such, current flows simultaneously into and through both thermoelectric stacks 600, 500b of the second pair 810 such via the respective contact layers 611 , 511. The current flows through both thermoelectric units 600, 500b (as described above in relation to figures 6A and 5A respectively) to exit the thermoelectric stacks 600, 500b on the second side of the thermoelectric stacks. The current then combines and exits the second pair 810 via a common output 801.

Figure 9 shows a schematic representation of the thermoelectric device 800 of the present invention incorporated into an electric circuit 900. The thermoelectric device 800 (which may be any suitable and/or desirable combination of embodiments discussed herein, e.g. any suitable combination of thermoelectric stacks 500, 600, 700 and/or in any suitable arrangement of a thermoelectric array) is disposed on a substrate 920 which is positioned proximate to a heat source and thus temperature gradient 905. The thermoelectric array 800 is electrically connected to a(n electrical) load 910, e.g. which consumes the electrical power generated by the thermoelectric device when in operation.

It will be appreciated that the (electrical) load 910 may be any suitable and/or desirable electrical device that consumes electrical power. In preferable embodiments the electrical device may comprise a wearable electronic device, for example, a wearable lighting system (e.g. attached to the front of a pair of spectacles or integrated into clothing), an electronic (e.g. smart) watch or any other suitable device that may be (at least integrated into an item which is) worn.