Semiconductor device manufacturing: process – Making device or circuit responsive to nonelectrical signal – Responsive to electromagnetic radiation
Patent
1997-04-17
1999-11-30
Dutton, Brian
Semiconductor device manufacturing: process
Making device or circuit responsive to nonelectrical signal
Responsive to electromagnetic radiation
438 95, 438102, H01L 2100, H01L 2106
Patent
active
059941634
DESCRIPTION:
BRIEF SUMMARY
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a method of manufacturing thin-film solar cells.
2. Description of the Related Art
CuInSe.sub.2 (copper indium selenide)--thin-film solar cells are normally produced by depositing a molybdenum (Mo) back contact onto a substrate, for instance a glass substrate. Copper, indium and selenide are then deposited onto the back contact to form a CuInSe.sub.2 layer, the CuInSe.sub.2 being formed by chemical reaction in a selenium-containing atmosphere. In this stage of manufacture, the structure is subjected to a temperature in the range of 350-600.degree. C.
The CuInSe.sub.2 layer is a p-type semiconductor. An n-type semiconductor is deposited on the CuInSe.sub.2 layer to form a pn-junction, which forms the actual solar cell. The n-type semiconductor is most often comprised of a thin layer of CdS and a much thicker layer of ZnO, which provides the best structure. The ZnO layer forms a front side contact at the same time.
It is desired to increase the efficiency of solar cells of this kind.
The present invention provides a method of manufacturing solar cells which greatly increases the efficiency of the solar cell produced.
SUMMARY OF THE INVENTION
Accordingly, the present invention relates to a method of manufacturing thin-film solar cells wherein a structure which includes a metal layer that forms an electrical back contact in the solar cell is coated with a layer of copper indium selenide (CuInSe.sub.2) in a manufacturing stage. The back contact is applied to a substrate, wherein the method is characterized by applying a layer of alkali metal to the structure prior to applying the CuInSe.sub.2 layer.
According to one particularly preferred embodiment of the invention, the alkali metal that is applied to the structure prior to applying the CuInSe.sub.2 layer is sodium (Na) or potassium (K).
By copper indium selenide layer as used in the present context and in the claims, is meant a copper indium selenide layer of different compositions and containing different alloying substances, primarily gallium and sulphur. The term copper indium selenide as used here concerns primarily the compounds CuInSe.sub.2, CuInxGa.sub.1-x Se.sub.2 and CuInxGa.sub.1-x SySe.sub.2-y.
The invention will be described below with reference to a layer of copper indium selenide that has the formula CuInSe.sub.2.
BRIEF DESCRIPTION OF THE DRAWINGS
The present invention will now be described in more detail partly with reference to an exemplifying embodiment of the invention shown in the accompanying drawing, FIG. 1 illustrates a solar cell structure.
DESCRIPTION OF THE PREFERRED EMBODIMENTS
The present invention is based on the understanding that when sodium or elementary potassium in the form of elementary sodium or potassium, or a compound in which these basic substances are present, is applied to the surface on which the CuInSe.sub.2 layer is to be built-up, for instance to the molybdenum layer, the grains in the polycrystalline CuInSe.sub.2 film will be orientated more in a columnar structure. The grains will also be larger and the structure more dense. The resistivity in the CuInSe.sub.2 layer is also reduced, meaning that a more effective p-doping is obtained, therewith resulting in a higher cell voltage.
Alkali metals other than sodium and potassium will provide the same effect. This applies at least to lithium, which has a low atomic weight.
FIG. 1 is a schematic sectional view of a thin-film solar cell. The substrate on which thin-film solar cells are built up may be large in size, for instance have a size of 1.times.0.4 meter. The substrate surface will therewith carry a very large number of cells that connect together electrically. FIG. 1 shows only one part of one such cell. The technique of producing a large number of separate but electrically connected cells on a substrate surface is well known to the art and will not be described in detail here.
A solar cell to which the invention can be applied nay be constructed in the following way.
REFERENCES:
patent: 4623601 (1986-11-01), Lewis et al.
patent: 4873118 (1989-10-01), Elias et al.
patent: 4915745 (1990-04-01), Pollock et al.
patent: 5028274 (1991-07-01), Basol et al.
patent: 5626688 (1997-05-01), Pabst et al.
patent: 5730852 (1998-03-01), Bhattacharya et al.
V.N. Vysotskii et al., "Photovoltaic Cells with Aluminum Contacts and a Base Partially Doped with Lithium", Applied Solar Energy, vol. 3, No. 27, 1991, pp. 16-19.
Bodeg.ang.rd Marika
Hedstrom Jonas
Stolt Lars
Dutton Brian
Mangels Alfred J.
Nordic Solar Energy AB
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