The invention concerns a thin thermoelectric layer used in

installations in which heat exchange takes place, in particular central heating and/or domestic water installations.

The market today expects new technical solutions and devices able to serve a growing number of functions, while at the same time getting more and more universal. Moreover, the entire industry is taking intense effort to develop new methods of generating electric energy. The majority of the micro-generating devices currently available in the market are based on principle of conversion of some form of kinetic energy to electric energy. Known are solutions employing different kinds of reciprocating engines, Stirling engines, turbines, etc. The solutions are characterised by

substantial limitations resulting from the high level of their complexity which entails high production cost, as well as by low reliability and high costs related to ensure the required maintenance.

Known are thermoelectric devices employing the Seebeck effect, which enable generation of electric energy. The devices contain

thermoelectric technical means where the temperature difference between specific areas enables generation of electric energy.

The current state of the art in the area of thermoelectric coatings implies that no solution has been found yet which would provide instruction on how to apply thermoelectric composites in a comprehensive manner and use them in devices. There are, however, some scientific publications which discuss specific methods of manufacturing the semiconductor components only, intended for thermocouples.

It should also be mentioned here that attempts are made to lay layers of bismuth telluride under the thermal spray method. Because of its high imprecision, however, the method proves poorly effective, and the produced systems of poor performance. Because of the open structure of the semiconductor junctions of the 'p' and 'n' type, the systems cannot be used safely.

Currently, the market is saturated only as concerns prefabricated

thermocouples. Their fairly substantial limitations stem from their absolute lack of formability and their standardized sizes.

Recently, however, a new application group has been developed for the electricity generating thermocouples: they are used to generate electricity in the so-called hiking power generators. The devices employ heat energy to enable charging small receivers. Because of the size of the target market, however, and the technical solutions used one can hardly speak about industrial scale here. The heretofore experimental attempts at using prefabricated thermocouple modules do not stand any true chance of commercialization because of their production and size-related limitations. Another factor which effectively hampers the development of this specific industry branch is the high unit cost of thermocouples.

Known from patent document CN 104538542 (A) is a method of producing a multilayer coating of thermoelectric materials used in the manufacturing of thermoelectric devices generating electric energy, where the method employs the method of physical gaseous phase deposition.

Layers of thermoelectric materials are applied to the appropriately selected base under the are magnetron sputtering method, where each individual layer is more than 5 nm thick.

The purpose of the invention is to develop a thermoelectric generator in the form of a thin layer which, when applied to those elements of devices in which heat exchange occurs, will pertain to higher energy efficiency of those devices which will at the same time produce electric energy used to supply electronic accessories or external devices, or delivered back to the power grid. In addition, the purpose of the invention is to solve the problems discussed in the first paragraphs hereof by providing technical means which would overcome low efficiency of thermoelectric devices and reduce their production costs.

The purpose has been achieved by developing a thin thermoelectric coating.

A thin thermoelectric coating, the functioning of which is based on the Seebeck effect, having a thermoelectric layer with semiconductor elements 'p' and 'n' interconnected in series, according to the invention is characterised in that it is produced under the PVD (Physical Vapour Deposition) technology, where the semiconductor elements of the thermoelectric layer are formed into semiconductor sub-layers 'p' and 'n' which do not contact each other, the thickness of which ranges from 1 μηι to Ι Ομιη, where the sub-layers are interconnected in series with thin-layered conducting elements fitted with connection ends to evacuate the generated electric energy, where the thermoelectric coating is insulated on both sides with layers of electrical insulator based on inorganic oxides.

Preferably, the width of each semiconductor sub-layer 'p' and 'n' ranges from 0.1mm to 2mm.

Preferably, the semiconductor sub-layers 'p' and 'n' of the thermoelectric layer are formed into alternating rings.

Preferably, the thin-layered conducting elements are made of copper and preferably their thickness falls within the range from 1 μιη to 5 μτη.

Preferably, the electrical insulator layers are produced based on A1 ₂ 0 ₃ or Si0 ₂ or MgO.

The invention enables additional production of electric energy obtained using the thermoelectric coating embedded in the devices. The solution according to the invention is advantageous in that it does not involve noise or vibration generation thanks e.g. to the absence of any movable elements. Moreover, it ensures generation of electricity based on temperature difference directly, while bypassing the conversion of kinetic energy, which will translate to high reliability while avoiding any increase in device maintenance costs.

The electric energy produced can find different applications, e.g. in:

- supplying power to electrical sub-assemblies of a complete device, such as control elements or pumping systems (improving energy efficiency)

- building autonomous units independent of external power supply

- delivering energy back to the local power network (reducing the

household demand for electric energy)

- delivering energy back to the power grid (micro sources, prosumer, citizen energy)

These and other characteristics of the invention will be clear from the following description of a preferential form of embodiment, given as a non- restrictive example, with reference to the attached drawing wherein the coating is shown in cross-section.

A thin thermoelectric coating, the functioning of which is based on the Seebeck effect, has a thermoelectric layer 1 with semiconductor elements 'p' and 'n', a series connection between the semiconductor elements 'p' and 'n' achieved using thin-layered conducting elements 2a, 2b, and electrical insulator layers 3a, 3b. The coating layers are produced under the PVD technology e.g. by: evaporation, laser ablation, magnetron sputtering, filtered cathodic arc deposition, or electron beam PVD. The semiconductor elements 'p' and 'n' of the thermoelectric layer 1 take the form of semiconducting sublayers not contacting each other, formed into alternating rings 'p' and 'n', the thickness d _{ of which ranges from l um to 10 μπι, preferably amounting to 5 μιτι, and the width of which falls within the range from 0.1mm to 2mm, preferably amounting to 1mm, where the rings are interconnected in series with thin-layered conducting elements 2a, 2b made of copper, the thickness d ₂ of which ranges from 1 to 5 μ ^η ι, preferably amounting to 3 μηι, fitted with connection ends 4, 5 to evacuate the generated electric energy. The semiconductor layers of the 'p' and 'n' types can be made of the following material groups: lead telluride; tin selenide; telluride, antimony, and bismuth compounds; inorganic occlusion compounds; skutterudite; semi-Heusler compounds; silicon compounds; and germanium compounds. Each layer 3a, 3b of electrical insulator is produced based on inorganic oxides, such as: A1 ₂ 0 ₃ or Si0 ₂ or MgO. The total thickness of the coating is 50 μηι or less.

First, the process of producing the electric insulator layer 3 a should be performed in the technological chamber, thanks to which the

thermoelectric layer 1 will be electrically independent of the base 6. The electrical insulator layer must be homogenous and continuous in structure. It will make it highly resistant to avalanche breakdown. Then,

appropriately located thin-layered conducting elements 2a should be made, which will form the basis and serve as electrical connection between the semiconductor sub-layers 'p' and 'η'.

There are many materials which can serve the function. Copper seems a good choice because of the ease of deposition and good conductivity.

Thanks to the interconnection between two different semiconductor layers 'p' and 'n' achieved using conducting elements 2a, 2b it will be possible to achieve the flow of current whenever the coating is exposed to temperature difference. The material should be selected according to the criteria of e.g. expected performance, the ensuing thermoelectric efficiency (ZT), and the anticipated range of temperatures to which the coating will be exposed during operation. In the next step, the appropriately located semiconductor sub-layers 'p' and 'n' should be made. Then, appropriately located thin- layered conducting elements 2b should be produced to close the electrical circuit of the thermoelectric layer 1. The last step consists in the producing of the second layer 3b of the electrical insulator.

In accordance with Seebeck's theory, a difference in temperature on two sides of the coating triggers orderly movement of charges in the semiconductor sub-layers 'p' and 'n' contained in the thermoelectric layer 1. Due to the series connection between the sub-layers, a difference of potential occurs between the outermost connection points, i.e. ends 4, 5. The thus-produced energy can be used to supply power to electronic accessories or external devices, or delivered back to the power grid.