Batteries: thermoelectric and photoelectric – Photoelectric – Cells
Patent
1994-06-22
1996-01-09
Weisstuch, Aaron
Batteries: thermoelectric and photoelectric
Photoelectric
Cells
136256, 136263, 257465, H01L 3106
Patent
active
054825709
DESCRIPTION:
BRIEF SUMMARY
FIELD OF THE INVENTION
The invention relates to a photovoltaic cell and more specifically to a cell of this type comprising a junction exhibiting a high roughness factor.
BACKGROUND OF THE INVENTION
The transformation of light energy into electrical energy using photovoltaic cells has been known for a long time and these cells are currently used in various electronic devices such as watches, calculators, cameras and the like.
These cells can be divided into four main types, namely metal-semiconductor (MS) junction cells of the Schottky diode type, metal-insulator-semiconductor (MIS) junction cells, semiconductor-insulator-semiconductor (SIS) junction cells, and homojunction or heterojunction cells.
The term junction is understood to mean the transition zone between a metal and a semiconductor or between two semiconductors of different types of conductivity.
In all known thin layer photovoltaic cells the semiconducting material used is always deposited in the form of a thin continuous and smooth layer on the surface of a substrate previously covered by a first transparent electrode made, for example, of metal. This layer of semiconducting material is then covered, depending on the type of cell, by one or more layers (semiconducting and/or insulating and/or conducting), the upper most layer forming the second electrode.
Although developments and improvements have been made to these photovoltaic cells over the last few years to improve their efficiency, this efficiency still remains relatively modest.
Moreover, the manufacture of these cells requires the use of materials of great purity and thus the use of sophisticated equipment installed in clean rooms, so that these cells still remain difficult to produce.
OBJECTS AND SUMMARY OF THE INVENTION
It is thus a main object of the invention to overcome the disadvantages of the above-mentioned prior art by providing a photovoltaic cell exhibiting a high rate of conversion of the energy of incident light into electrical energy per unit of surface and which is, moreover, simple to manufacture.
The object of the invention is therefore a photovoltaic cell comprising a substrate having a support face on which there is disposed a first electrode, a second electrode insulated from the first electrode by a plurality of layers having at least a first layer of a semiconducting material with an active junction at an interface thereof, characterised in that said active junction exhibits a developed surface area greater than its projected surface area.
This characteristic greatly increases the efficiency of collection of incident photons in relation to the cells of the prior art. This increase is essentially due to the multiple diffusion of the light in the semiconducting layer in association with the large active junction. The structure of the cell of the invention thus provides an improved efficiency per unit of surface area.
According to an advantageous feature of the invention, said active junction exhibits a roughness factor greater than 20.
It will be noted in this connection that the roughness factor is defined by the ratio between the real surface area and the projected surface area.
According to a first embodiment of the invention, said support face exhibits a developed surface area greater than its projected surface area and all said other layers extend successively on said support face.
This embodiment notably has the advantage of being simple since it only needs one mechanical or chemical treatment of the substrate.
According to a second embodiment of the invention, the first electrode exhibits a developed surface area greater than its projected surface area and all said other layers extend successively on said electrode.
According to a third embodiment of the invention, said first layer of semiconducting material exhibits a developed surface area greater than its projected surface area and all said other layers extend successively on said first layer of semiconducting material.
According to another advantageous feature of the invention common to the second
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patent: 4532537 (1985-07-01), Kane
patent: 4554727 (1985-11-01), Deckman et al.
patent: 4732621 (1988-03-01), Murata et al.
patent: 4851658 (1989-07-01), Murata et al.
Technical Digest of the International PVSEC-5 26 Nov. 1990, Kyoto, Japan pp. 701-704 Hezel et al. "Advantages of Textured Multicrystalline Silicon for MIS Inversion Layer Solar Cells".
Patent Abstracts of Japan vol. 12, No. 118 (E-600) 13 Apr. 1988 & JPA62 247 574 (Sanyo Electric Company Ltd) 28 Oct. 1987.
Patent Abstracts of Japan vol. 10, No. 39 (E-381) 15 Feb. 1986 & JPA60 195 979 (Handoutai Enerugii Kenkyusho KK) 4 Oct. 1985.
Patent Abstracts of Japan vol. 12, No. 49 (E-582) 13 Feb. 1988 & JPA62 198 169 (Fuji Electric Corp Res & Dev Ltd) 1 Sep. 1987.
Gratzel Michael
Meyer Tobias
Saurer Eric
Asulab S.A.
Weisstuch Aaron
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