Batteries: thermoelectric and photoelectric – Photoelectric – Cells
Patent
1995-05-31
1996-12-31
Weisstuch, Aaron
Batteries: thermoelectric and photoelectric
Photoelectric
Cells
136255, 136256, 136258, 136261, 257431, 257436, 257438, 427 74, 437 2, H01L 3106, H01L 3118
Patent
active
055890083
DESCRIPTION:
BRIEF SUMMARY
FIELD OF THE INVENTION
The present invention relates to photovoltaic cells in general and, more particularly, to photovoltaic cells having a semi-conductor substrate, an emitter layer having a first conductivity type (p or n), a front passivation layer between the substrate and the emitter layer, a front transparent conductive layer, a rear passivation layer deposited on the rear surface of the substrate, and a reflective element comprising a rear transparent conductive layer, an adhesion layer and a reflective layer.
It also relates to a method for fabricating such a photovoltaic cell.
BACKGROUND OF THE INVENTION
The search for renewable energy sources which do not produce waste and are both ecologically acceptable and economically poses one of the greatest challenges of this era. One solution to the problem of providing "clean" energy is solar energy. Numerous types of solar energy collectors have been developed to transform solar energy into an energy form which is easier to store and transport, such as electrical energy, for example. Photovoltaic cells, currently called solar cells, function essentially according to the following principle: when a photon reaches a semi-conductor, it generates charge carriers by promoting electrons in the valence shell to the conduction shell and thus produces electron/hole pairs. Thus, an electromotive force is present on opposite sides of the junction and the semiconductor acts as an energy source.
Two methods of making such photovoltaic cells have been explored. One consists of using a crystalline material with high voltaic efficiency (greater than 10%) cut into plates. The other consists of depositing a thin layer of material with a lower efficiency (5% to 10%) on a large, inexpensive support (glass, stainless, plastic, etc.). This invention involves the former method.
Various methods have been developed for making photovoltaic cells from crystalline materials having high voltaic efficiency. However, these methods are not without shortcomings in terms of expensive fabrication costs and marginal outputs from the cells.
A first method of producing such cells consists of using thermal diffusion to dope a silicon substrate with an element such as boron or phosphorus at a temperature above 1,000.degree. C. This high temperature treatment consumes much energy and thus is costly; additionally, when a thin substrate is used at such a high temperature, it tends to break or bend. Consequently, solar cells produced by this method are quite expensive.
Other procedures have been explored to overcome these disadvantages. One of these consists of replacing the doping process with the deposition of a doped layer at a lower temperature. This is accomplished by depositing a thin layer of amorphous silicon of p type conductivity on a crystalline silicon substrate of n type conductivity at a temperature of less than 200.degree. C. Accordingly, a heterojunction of the type p
is obtained. Since it takes place at a lower temperature, this procedure consumes relatively little energy. In addition, the lower temperature reduces cross-contamination of the charge carriers caused by diffusion of impurities from the treatment chamber, a fact which improves cell output. However, the output is still marginal, as cross-contamination is not entirely eliminated.
In an attempt to eliminate this phenomena altogether, a procedure has been devised whereby an intrinsic layer of amorphous silicon is deposited between the crystalline silicon layer having n type conductivity and the amorphous silicon layer having p type conductivity. This cell, known as ACJ-HIT (Artificially Constructed Junction-Heterojunction with Intrinsic Thin layer), is fabricated using a low temperature method and provides an efficient output, since there is no cross-contamination and the p
type junction is abrupt.
Further attempts to increase photovoltaic cell efficiency have resulted in the development of semiconductive junctions on both substrate surfaces. To achieve this, the cell has a silicon substrate with p type conducti
REFERENCES:
patent: 5213628 (1993-05-01), Noguchi et al.
11th EC Photovoltaic Solar Energy Conference, 12 Oct. 1992, Montreux, CH pp. 617-620--R. Fluckiger et al. `Microcrystalline silicon prepared with the very high frequency glow discharge technique for p-i-n solar cell applications` see the whole document.
23rd IEEE Photovoltaic Specialists Conference, 10 May 1993, Louisville, USA pp. 839-844--R. Fluckiger et al. `Preparation of undoped and doped microcrystalline silicon (uc-Si:H) by VHF-GD for p-i-n solar cells` see the whole document.
Japanese Journal of Applied Physics., vol. 31 PT. 1, No. 11, Nov. 1992, Tokyo JP--pp. 3518-3522--M. Tanaka et al. `Development of new a-Si/c-Si heterojunction solar cells: ACJ-HIT (Artificially Constructed Junction-Heterojunction with Intrinsic Thin-Layer)`.
Progress in Photovoltaics: Research and Application, vol. 1, No. 2, Apr. 1993, Chichester, GB pp. 85-92--M. Tanaka et al. "Development of new heterojunction structure (ACJ-HIT) and its application to polycrystalline silicon solar cells".
23rd IEEE Photovoltaic Specialists Conference, 10 May 1993, Louisville, USA pp. 878-884--D. Fischer et al. "Amorphous silicon solar cells with graded low-level doped i-layers characterised by bifacial measurements".
11th E. C. Photovoltaic Solar Energy Conference, 12 Oct. 1992, Montreux, CH pp. 1057-1060--T. Takahama et al. "High efficiency single- and poly-crystalline silicon solar cells using ACJ-HIT structure".
Universite De Neuchatel
Weisstuch Aaron
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