FIELD OF INVENTION

The present invention relates to a photovoltaic device and more particularly, the present invention relates to a photovoltaic cell integrated with at least one sensor.

BACKGROUND OF THE INVENTION

Photovoltaic cells convert energy from sunlight into electrical energy which can be used to power up electronic devices. A conventional photovoltaic cell comprises of a single or multiple p-n or p-i-n junction(s), a back contact, and front contact(s) connected to a plurality of metal collector fingers and busbar structures.

Photovoltaic cells are often placed in an open environment to allow it to absorb sunlight for supplying electrical energy to electronic devices. Since it is placed in an open environment, it is useful to integrate photovoltaic cells with a sensor device for measuring environmental parameters. At present, there are prior arts that integrate photovoltaic cells with a sensor device to detect light properties such as ultraviolet, infrared and light sensor. US Patent No. 7,241 ,999 discloses the use of a photovoltaic element as sensor for checking the functionality of transmitters in the infrared range.

US Patent Application No. 20070145499 discloses a photovoltaic ultraviolet sensor that comprises a zinc oxide single crystal substrate. On the +c face of the zinc oxide single crystal substrate, an ultraviolet receiver is formed. The exemplary ultraviolet receiver includes a Schottky electrode which, when receiving ultraviolet rays, produces a voltage in cooperation with the zinc oxide single crystal substrate. The ultraviolet sensor does not have any sensitivity to the visible rays. The ultraviolet sensor has a relatively fast response of several microseconds.

However, none of the prior arts integrates photovoltaic cells with sensor device to measure environmental parameters such as temperature, humidity, gas content and the like. The integration of photovoltaic cells with such sensor device needs to ensure that the sensor device does not heavily affect the electrical energy produced by either highly consuming the electrical energy produced by the photovoltaic cells or arranging the sensor device in a manner that limits the sunlight absorption area of the photovoltaic cells. Moreover, the integration must also consider the effect of exposing the sensor device to direct sunlight. The photovoltaic cells should also be able to integrate with an array of sensors to increase sensitivity and performance in sensing the environment parameters.

Therefore, there is a need to provide a photovoltaic device that integrates photovoltaic cells with at least one sensor device for sensing environmental parameters such as temperature, humidity, gas content and the like.

SUMMARY OF INVENTION

The present invention relates to a photovoltaic device (1 , 2, 3) for generating electricity and sensing environmental parameters. The photovoltaic device (1 , 2, 3) comprises a semiconductor junction (12), wherein the semiconductor junction (12) functions to generate electricity from light, a front contact (13, 23, 33) provided on top of the semiconductor junction (12), wherein the front contact (13, 23, 33) is to allow connection with an external circuit for supplying electricity, a back contact (14) provided underneath the semiconductor junction (12), wherein the back contact (14) is to allow connection with an external circuit for supplying electricity, at least one metal collector finger (15, 25, 35) provided on top of the semiconductor junction (12), wherein the at least one metal collector finger (15, 25, 35) is to allow current flow from the semiconductor junction (12) to the front contact (13, 23, 33), and at least one busbar (16, 26, 36) connected to the front contact (13, 23, 33) and the at least one metal collector finger (15, 25, 35). Moreover, the photovoltaic device (1 , 2, 3) is characterised in that it further comprises at least one sensor (11, 21, 31), and wherein the at least one sensor (11, 21, 31) is a portion of the at least one metal collector finger (15, 25, 35) shaped in a serpentine manner.

Preferably, the semiconductor junction (12) is a single or multiple type junction(s). Moreover, the semiconductor junction is preferably either a p-n junction, p-i-n junction, schottky junction or any combination thereof.

Preferably, the at least one sensor (11, 21, 31) occupies an area of less than 300 m ² . Preferably, the at least one sensor (15, 25, 35) is provided with two electrical contact pads (17, 27) in between the serpentine structure for connection with an external sensing circuit. Preferably, the at least one sensor (15, 25, 35) is provided in between the at least two busbars (16, 26, 36), and wherein each busbar (16, 26, 36) is provided with electrical contact pad (37) for connection with an external sensing circuit.

Preferably, the at least one metal collector finger (15, 25, 35) and the at least one sensor (11, 21, 31) are made of metallic conductive material.

Preferably, the at least one sensor (15, 25, 35) is covered with metal oxide membrane to sense specific ions, and wherein the metal oxide membrane is suitably made out of one of the following materials: tin oxide (Sn0 ₂ ), tungsten oxide (WO _x ), tantalum pent-oxide (Ta ₂ 0 ₅ ), aluminium oxide (Al ₂ 0 ₃ ) copper oxide (CuO), iron oxide (Fe ₂ 0 ₃ ), titanium oxide (TiO), Neodymium Oxide (Nd ₂ 0 ₃ ) or zinc oxide (ZnO).

Preferably, the at least one sensor (15, 25, 35) is covered with nanotubes or nanowires membrane.

BRIEF DESCRIPTION OF THE DRAWINGS

The accompanying drawings, which are incorporated in and constitute a part of the specification, illustrate embodiments of the invention and, together with the description, serve to explain the principles of the invention.

FIG. 1a illustrates a top view of a photovoltaic device (1) in accordance with a first embodiment of the present invention.

FIG. 1b illustrates a cross sectional view of a photovoltaic device (1) in accordance with a first embodiment of the present invention.

FIG. 2 illustrates a top view of a photovoltaic device (2) in accordance with a second embodiment of the present invention. FIG. 3 illustrates a top view of a photovoltaic device (3) in accordance with a third embodiment of the present invention.

DESCRIPTION OF THE PREFFERED EMBODIMENT

A preferred embodiment of the present invention will be described herein below with reference to the accompanying drawings. In the following description, well know functions or constructions are not described in detail since they would obscure the description with unnecessary detail. Referring now to FIGS. 1(a-b), there is provided a first embodiment of a photovoltaic device (1) wherein a photovoltaic cell is integrated with a sensor (11). The photovoltaic device (1) has dual function whereby it is able to generate electricity from light as well as sensing environmental parameters such as temperature, humidity, gas content and the like. The photovoltaic device (1) comprises a p-n junction (12), a front contact (13), a back contact (14), a metal collector finger (15), two busbars (16), and a sensor (11).

The p-n junction (12) comprises two separate semiconductors sandwiched together. Preferably, the p-n junction comprises a negative-type silicon (12a) which has excess electrons sandwiched with a positive-type silicon (12b) which has excess holes. Sandwiching the negative-type silicon (12a) and the positive-type silicon (12b) together creates electron-hole pairs at their interface, thereby creating an electric field. When sunlight, in the form of photons, is provided, its energy breaks apart the electron-hole pairs. Each photon with enough energy frees an electron, and resulting in a free hole as well. If this happens close enough to the electric field, or if free electron and free hole happen to wander into its range of influence, the field will send the electron to the negative-type silicon (12a) and the hole to the positive-type silicon (12b). If an external circuit is connected between the front contact (13) and the back contact (14), electrons will flow through the circuit to the positive-type silicon (12b) to unite with the holes. The electron flow provides the current, and the electric field causes a voltage.

The front and back contacts (13, 14) are provided to allow connection with an external circuit for supplying electrical power. The front contact (13) is provided on top of the negative-type silicon (12a), whereas the back contact (14) is provided underneath the positive-type silicon (12b). The front contact (13) is connected to the metal collector finger (15) through the busbars (16).

The metal collector finger (15) is a finer area of metallization to allow the current flow from the negative-type silicon (12a) to the front contact (13) through the busbars (16). The metal collector finger (15) is integrated with a sensor (11) on top of the p-n junction (12). The sensor ( 1) is a resistive type sensor wherein a portion of the metal collector finger (15) is shaped in a serpentine manner and it is provided with two electrical contact pads (17) in between the sensor (11) for connection with an external sensing circuit. The sensor (11) occupies a small area of the metal collectors (15) to minimize the impact on the overall efficiency of the p-n junction (12) to generate electrical power. Preferably, the sensor (11) occupies an area of less than 300 μιτι ² . Preferably, the metal collector finger (15) and sensor (11) are made of metallic conductive material such as aluminium, silver, gold, platinum, tungsten, copper, or nickel. Moreover, the metal collector finger (15) which includes the sensor (11) is preferably formed by sputtering, evaporation, screen printing, electroplating or chemical vapour deposition.

Alternatively, the sensor (11) can be covered with sensing membrane to sense specific ions, and thus, allowing multiple sensor types to be integrated onto the photovoltaic device (1). The sensing membrane may further improve the sensor sensitivity by having a large surface to volume ratio. The sensing membrane is preferably a metal oxide membrane or a nanostructure membrane. The metal oxide membrane can be made of but not limited to tin oxide (Sn0 ₂ ), tungsten oxide (WO _x ), tantalum pent-oxide (Ta ₂ 0 ₅ ), aluminium oxide (Al ₂ 0 ₃ ) copper oxide (CuO), iron oxide (Fe ₂ 0 ₃ ), titanium oxide (TiO), Neodymium Oxide (Nd ₂ 0 ₃ ) or zinc oxide (ZnO). The nanostructure membrane can be made of nanotubes or nanowires such as single- walled carbon nanotubes (SWNTs), multi-walled carbon nanotubes (MWNTs), silicon nanowires, tungsten nanowires, gold nanowires.

The output from the sensor (11) is measured via the two electrical contact pads (17) when there is a change in resistance which is determined by the dimensions and conductive material properties of the sensor (11), using the formula below: R = Ps L / W

where p _s is the sheet resistance of the conductive material, L is the length of the sensor (11) and W is the width of the sensor (11). In order to use the sensor (11) for temperature sensing, the sensor (11) comprises only the serpentine structure of the metal collector finger (15). There is a linear relationship between the change in temperature and the change in resistivity and therefore, a change in temperature affects the resistivity of the sensor (11). In order to use the sensor (11) for gas or humidity sensing, the sensor (11) comprises the serpentine structure of the metal collector finger (15) with a thin film or nanostructures on top of it. Preferably, the serpentine structure is covered with polyimide film or carbon nanotubes for humidity sensing to absorb moisture in the environment. Thus, a change in humidity affects the resistivity of the sensor (11). For gas sensing application, the serpentine structure is preferably coated with metal oxide thin film or nanowires. The reaction between the metal oxide and gas induces a change in the resistivity of the sensor (11).

Referring now to FIG 2, there is provided a second embodiment of a photovoltaic device (2) wherein an array of sensors (21) are integrated in series to a metal collector finger (25). The photovoltaic device (2) has dual function whereby it is able to generate electricity from light as well as sensing environmental parameters such as temperature, humidity, gas content and the like. The photovoltaic device (2) comprises a p-n junction (not shown), a front contact (23), a back contact (not shown), a plurality of metal collector fingers (25), three busbars (26) and an array of sensors (21).

The p-n junction (not shown) comprises two separate semiconductors sandwiched together. Preferably, the p-n junction (not shown) comprises a negative- type silicon sandwiched with a positive-type silicon. The p-n junction is functioned to generate electricity from absorbing light.

The front contact (23) is provided on top of the p-n junction (not shown), whereas the back contact (not shown) is provided underneath the p-n junction (not shown). The front and back contacts are provided to allow connection with an external circuit for supplying electrical power. The front contact (23) is connected to the plurality of metal collector fingers (25) through the busbars (26).

The plurality of metal collector fingers (25) is finer areas of metallization to allow the current flow from the p-n junction (not shown) to the front contact (23) through the busbars (26). One of the metal collector fingers (25) is provided with an array of sensors (21). The sensors (21) are serially integrated to the metal collector finger (25). Each sensor (21) is a resistive type sensor wherein a portion of the metal collector finger (25) is shaped in a serpentine manner and it is provided with two electrical contact pads (27) in between the serpentine structure for connection with an external sensing circuit.

Referring now to FIG. 3, there is provided a third embodiment of a photovoltaic device (3) wherein an array of sensors (31) are serially integrated. The photovoltaic device (3) has dual function whereby it is able to generate electricity from light as well as sensing environmental parameters such as temperature, humidity, gas content and the like. The photovoltaic device (3) comprises a p-n junction (not shown), a front contact (33), back contact (not shown), a plurality of metal collector fingers (35), two busbars (36) and an array of sensors (31).

The p-n junction (not shown) comprises two separate semiconductors sandwiched together. Preferably, the p-n junction (not shown) comprises a negative- type silicon sandwiched with a positive-type silicon. The p-n junction (32) is functioned to generate electricity from absorbing light.

The front contact (33) is provided on top of the p-n junction (not shown), whereas the back contact is provided underneath the p-n junction (not shown). The front and back contacts are provided to allow connection with an external circuit for supplying electrical power. The front contact (33) is connected to the plurality of metal collector fingers (35) through the busbars (36) on top of the p-n junction (not shown).

Each metal collector finger (35) is integrated with a sensor (31). Each sensor (31) is a resistive type sensor wherein a portion of the metal collector finger (35) is shaped in a serpentine manner. Each sensor (31) is serially connected to each other through the busbars (36). One end of the busbars (36) is connected to the front contact (33) whereas another end of the busbars (36) is provided with electrical contact pad (37) for connection with an external sensing circuit. The serial integration of sensors (31) may further improve the photovoltaic device (3) sensitivity and performance in sensing environmental parameters.

Although described in the description that the p-n junction is used to generate electrical power, any other semiconductor junction that is capable of generating electrical power from light can be used. Non-limiting example of the semiconductor junction may include p-i-n junction, schottky junction or any combination thereof.

While embodiments of the invention have been illustrated and described, it is not intended that these embodiments illustrated and describe all possible forms of the invention. Rather, the words used in the specifications are words of description rather than limitation and various changes may be made without departing from the scope of the invention.