GB2516937A

GB2516937A - Method of Producing a Photovoltaic Cell

Info

Publication number: GB2516937A
Application number: GB1314170.0A
Authority: GB
Inventors: David Boys
Original assignee: Individual
Current assignee: Individual
Priority date: 2013-08-07
Filing date: 2013-08-07
Publication date: 2015-02-11
Also published as: GB201314170D0

Abstract

A method of producing a photovoltaic cell includes the step of extruding at least one of an upper electrode layer 15, at least one semiconductor layer 17 or a lower electrode layer 21 which are then connected together. The upper and/or lower electrode may include a conductive polymer. The semiconductor layer maybe a crystalline semiconductor, or an organic semiconductor. The organic semiconductor can be selected from a semiconducting polymer or a fluorine derivative or an organometal compound. A UV protective layer may be formed on the upper electrode. The Photovoltaic cell may be attached to a vehicle of a building. The photovoltaic cell may be made from plural extruders, which converge so that the layers can be formed simultaneously to produce a photovoltaic cell.

Description

Method of Producing a Photovoltaic Cell The present invention relates to a process for producing a photovoltaic cell. More particularly, the invention relates to a process for producing a photovoltaic cell wherein at least one of the component layers of the photovoltaic cell is formed by extrusion.

Photovoltaic (PV) cells are well-known and are becoming more widespread on homes and office buildings. Photovoltaic cells convert sunlight into electricity. Light shining on a photovoltaic cell produces both a current and a voltage to generate electric power. A standard FV cell has a semiconductor with an electrode attached to either side. Additional supports and electronics are added as required.

Silicon has long been the material of choice for forming the semiconductor layer in a photovoltaic cell. Latterly, other materials have been considered which have an improved performance over silicon, for example cadmium-telluride. Organic photovoltaic cells (OPV5) are a promising cost- effective alternative to silicon-based solar cells, and posses light-weight, low-cost and flexibility advantages.

An emerging manufacturing process is to print semiconductors onto plastic substrates to form a photovoltaic cell. However, printing films has a number of drawbacks. Such drawbacks include the fact that it is difficult to control the thickness of the film after it has been printed. Very often, the printed film is moved from one roll to another for storage where it is likely to be deformed. Also, if the printed layer is rather thin then it may not be possible to absorb the full range of the solar energy spectrum and this will result in wasted photons. Further, printed PV cells are not very efficient and require a far larger area than silicon-based solar cells to generate the same amount of electricity.

Therefore, there is a requirement to improve the process of producing a photovoltaic cell whilst maintaining the desired low cost of manufacture.

The present invention provides a method of producing a photovoltaic cell including the steps of extruding at least one of: an upper electrode layer; at least one semiconductor layer; or a lower electrode layer.

An advantage of the extrusion process is that the materials to be used can be can be heated to temperatures above their burning points as they are kept moving. This means that the number of materials which can be used in producing photovoltaics is now increased due to the processing technique. A further advantage is that the extrusion process allows one to set the desired thickness of each component layer of the photovoltaic cell.

Another advantage is that the extrusion process automatically achieves sterile encapsulation between the layers whereas known processes for producing PV cells require clean-room conditions. The upper electrode is the electrode which faces the sun when in use. The lower electrode layer is the layer which is attached to the semiconductor and which does not face the sun when in use.

In an embodiment, all of the upper and lower electrode layers and the at least one semiconductor layer are produced by extrusion. This minimises the cost of producing a photovoltaic cell compared to the known methods.

In another embodiment, the at least one semiconductor layer can be produced by a number of small extruders so that a different thickness of layer is provided. The layers are fused together so that each layer can absorb a different wavelength of light. This is known as a tandem cell and the layers can be optimised to each section of the spectrum resulting in less loss. Each extruder can contain the same or different semiconductor material.

In another embodiment, at least one extruder is used for each of the layers. This allows different temperatures to be applied to each of the component materials. In particular, two different semiconductors can be used together to create a heterojunction. Each semiconductor can be extruded either at the same time or independently.

The extrusion process can produce a blown or cast film. The cast film process is used for very tight tolerances of thin film or for low viscosity resins.

Most cast film lines manufactured today are co-extrusion lines, which combine many layers into a product through multi-manifold dies and distribution blocks or single-manifold dies with the aid of co-extrusion feedblock.

In an embodiment, the output of the extrusion is convergent so that the component layers of the photovoltaic cell can be formed simultaneously. The convergence allows that layers to join to one another to produce the sheet of photovoltaic material. This process is much more cost effective than the process of producing each layer as a separate sheet and then attaching them together is avoided.

In an embodiment, the at least one semiconductor layer is a crystalline semiconductor such as Il-VI, Ill-V or IV-IV semiconductor, e.g. silicon, CdSe, titania nano crystals, CdTe, Cl(G)s, a-Si.

In an embodiment, the at least one semiconductor layer is extruded.

In an embodiment, the at least one semiconductor layer is made of an organic semiconductor such as a semiconducting polymer, fullerene derivative, or organometallic compounds. Suitable organic semiconductors include copper phthalocyanine, small molecular donor/fullerene acceptors or polymeric donor/tullerene acceptors as well as non-fullerene acceptors, tor example poly(lll-hexylthiophene)1050 and capper phthalocyanine/C60. By changing the length of the polymers and the functional groups attached thereto one can change the energy gap, which allows a chemical change in the material. As the optical absorption co-efficient of organic molecules is high, a large amount of light can be absorbed with a small amount of materials. Therefore, desired properties can be built into a PV cell by simply modifying the semiconductor material. An advantage of using organic semiconductors is that rigid supports are not needed and so the resulting PV cell can easily be put onto lightweight plastic which can be flexible. This allows the PV cell to be placed on all manner of surfaces such as on vehicles including aircraft an road vehicles, on buildings, including temporary buildings such as tents and inflatables.

In another embodiment, the lower electrode layer is made of any suitable material such as a metal or a conductive polymer. A preferred material is one which is predisposed to give away electrons. More particularly, the lower electrode layer includes nano particles.

In an embodiment, the upper electrode layer is made of any suitable material, for example indium tin oxide, which is transparent. This is used with traditional silicon cells. Where the photovoltaic cell is based upon organic semiconductors then the transparent conductive layer can be a transparent conductive polymer or glass, or similar substrate, with nano particles therein, for example silver impregnations. An indium-free high-transmittance low-surface-resistance multi-layer transparent conducting film can serve as this electrode.

The material chosen to form this layer should be transparent to allow photons to reach the underlying semiconductor layer(s) and which attracts electrons.

In an embodiment, a further layer can be provided onto which the lower electrode layer is placed. This backing layer can be used to give strength to the PV cell, which may be required if it is to be used in traditional areas such as on roofs. This layer can also be made by extrusion and can be joined after the other component layers of the PV cells have been formed or concurrently. Any suitable material can be used such as polyethylene and more particularly a linear low density polyethylene which can be made from recycled materials. The material needs to be etched or abraded to enable electrical contacts to be made with the lower electrode.

In an embodiment, a further layer is provided on the PV cell. This layer is a U.V. protective layer and is provided on the upper electrode layer. This can be made of any suitable material such as ethylene tetrafluoroethylene co-polymer (ETFA), fluorinated ethylene propylene (FEP), and polyvinyl fluoride, or titanium dioxide. This layer needs to be etched or abraded to enable electrical contacts to be made with the upper electrode layer. This layer can also be made by extrusion and can be joined after the component layers of the PV cells have been formed or concurrently with the other electrode layer(s) and/or semiconductor layer(s).

The invention also provides a photovoltaic cell produced by the method described herein. The photovoltaic cell can be manufactured as an article or a desired shape instead of a flat sheet.

The invention extends to any novel feature described or illustrated herein or inventive combination of features described or illustrated herein. The invention may be performed in various ways and an embodiment thereof will now be described by way of example only, reference being made to the accompanying figures in which: Figure 1 shows a schematic of an extruding device used according to the method described herein to produce a photovoltaic cell; and Figure 2 shows a photovoltaic cell made by the described method.

Figure 1 shows a preferred embodiment wherein the extruder device simultaneously produces the component layers of a photovoltaic cell simultaneously. There are provided a number of extruders 12, 14, 16, 18, 20 and 22. Each of these extruders contains a specific material used to form a layer of a photovoltaic cell where production also requires a protective layer on the upper electrode layer. Extruder 12 can be filled with a material such as ETFA, FEP, polyvinyl fluoride or titanium dioxide to protect the cell beneath it. It is also possible to use a thin layer of dielectric material or to provide an anti-reflective coating of zinc sulphide and magnesium fluoride. Extruder 14 is loaded with material to produce a transparent upper electrode layer. Extruder 16 is filled with a semiconductor, for example an organic semiconductor.

Extruder 18, when required, is filled with another semiconductor so that when it is extruded a heterojunction is formed between the two semiconductor layers.

Extruder 20 is filled with a material to form a lower electrode layer. Finally, extruder 22 can be used to provide a backing layer which can give strength to the photovoltaic cell.

Figure 2 shows a profile view of a photovoltaic cell manufactured according to the method described herein. Layer 13 is a Liv. protective layer.

Layer 15 is a transparent upper electrode layer. Layer 17 is a first semiconductor layer on top of a second semiconductor layer 19 with a heterojunction 24 formed therebetween. Layer 21 is a lower electrode layer which is joined to a backing layer 23 which gives strength to the cell.

The above embodiment is just one example of the invention defined by the claims. Modifications, variants, additions or omissions will be apparent to the skilled addressee. For example, in an alternative embodiment, not all of these extruders will be necessary as it may be that some of the layers making up the photovoltaic cell can be preformed. For example, one or more semiconductor layers could be provided onto which the electrode layers can be placed. The extruders can be reordered so that the film is produced in a different orientation.

It is to be understood that light beyond the visible spectrum, such as infra-red and ultraviolet, and radiation can be used instead of, or in addition to, visible light for the generation of electricity.

The features disclosed in the foregoing description, or the following claims, expressed in their specific forms, or interims of a means for performing the disclosed method may, separately, or in any combination of such features, be utilised for realising the invention in diverse forms thereof.

Claims

Claims 1. A method of producing a photovoltaic cell including the steps of extruding at least one of: an upper electrode layer; at least one semiconductor layer; or a lower electrode layer.
2. A method according to claim 1 wherein all of the upper and lower electrode layers and the at least one semiconductor layer are produced by extrusion.
3. A method according to either of claims 1 or 2 wherein at least one extruder is used for each of the layers.
4. A method according to any preceding claim wherein the output of the extruders converge so that the layers can be formed simultaneously to produce a photovoltaic cell.
5. A method according to any preceding claim wherein the upper and/or lower electrode layer includes a conductive polymer.
6. A method according to any preceding claim wherein the upper and/or lower layer includes nanoparticles.
7. A method according to any preceding claim wherein the at least one semiconductor is a crystalline semiconductor.
8. A method according to any of claims 1-6 wherein the at least one semiconductor is an organic semiconductor.
9. A method according to any preceding claim wherein at least two semiconductor layers are used to produce a heterojunction.
10. A method according to claim 8 or claim 9 wherein the organic semiconductor is selected from: a semiconducting polymer; a fluorine derivative; or an organometallic compound.
11. A method according to any preceding claim wherein a backing layer is provided onto which the lower electrode is placed or formed.
12. A method according to any preceding claim wherein a U.V. protective layer is provided on the upper electrode layer.
13. A photovoltaic cell comprising at least one of: an upper or lower electrode layer and; at least one semiconductor layer, produced by extrusion.
14. A photovoltaic cell according to claim 13 wherein each of the upper and lower electrode layers and the at least one semiconductor are produced by extrusion.
15. A vehicle having a photovoltaic cell according to claim 13 or 14 attached thereto.
16. A building having a photovoltaic cell according to claim 13 or 14 attached thereo.
17. A method of producing a photovoltaic film substantially as hereinbefore described and with reference to the accompanying drawings.
18. A photovoltaic cell substantially as hereinbefore described and with reference to the accompanying drawings.