Batteries: thermoelectric and photoelectric – Photoelectric – Cells
Patent
1997-01-13
1999-08-10
Chapman, Mark
Batteries: thermoelectric and photoelectric
Photoelectric
Cells
438 97, 438488, H01L 3100
Patent
active
059353457
DESCRIPTION:
BRIEF SUMMARY
The present invention relates to the field of the conversion of radiated solar energy into electrical energy, based on the photovoltaic effect, more particularly in the increase in output and efficiency of the photocells or solar cells, and has for its object a process for production of a photovoltaic material or device which can particularly absorb infrared radiation and convert it with an efficiency significantly exceeding unity, the material or the device thus obtained and a photocell or photovoltaic cell comprising such a material or device.
At present, high quality solar cells assembled in modules and fabricated on an industrial scale have an output which is to say a maximum power ratio of peak/incident photovoltaic flux, of the order of 12 to 13%.
These cells, widely commercialized, are constituted of a monocrystalline silicon material and generally have a structure emitter/base/rear field with a single P-N junction.
Moreover, the surface exposed to the photonic radiation is normally subjected to a passivation operation and is coated with an anti-reflective surface.
There also exists solar cells, comprising a P-N junction, produced in limited series in laboratories and whose output is about 23%.
However, these cells of higher performance require, for their production, on the one hand a base material of the type silicon FZ ("Floating Zone") of excellent quality and, on the other hand, between thirty and sixty different steps for their fabrication, so as to obtain particularly a complex exposed surface (formed by a multitude of juxtaposed pyramids) capable of trapping the incident light.
There results a process of fabrication of the photovoltaic material and hence of the cells which is very difficult to industrialize and a high cost, because of the fact of the starting material and the complexity of the production of the cell, which is very high, limiting their application to very specific fields and situations.
Moreover, it has recently been proposed to produce photocells based on monocrystalline silicon partially modified so as to attempt to enlarge the natural absorption spectrum of the starting material, particularly in the infrared range, and thereby to increase the output of the resultant photocell.
More particularly, the proposals set forth consist, by an implantation of hydrogen and a consecutive thermal treatment, in transforming to the local level the crystalline structure of the silicon to create a buried layer provided with extrinsic levels.
These different experimental approaches are particularly described in the following articles: "35% Efficient Nonconcentrating Novel Silicon Solar Cell", J. Li et al., Appl. Phys. Lett., 60 (1992) 2240-2242; "A Study on Solar Cells Based on the "Junction Near Local Defect Layer" Design", C. Sumnote et al., 11th E.C. Photovoltaic Solar Energy Conference, Montreux, Switzerland, October 1992, pages 370 to 373 and "New Type of Silicon Material with High Quality Surface Layer on Insulating Defect Layer", Electronic Letters, 28 (1992) 652-653.
The most widespread practical embodiment of the proposals above is that known under the letters JNDT "Junction Near local Defect Layer") and consists in implanting through a mask a discontinuous substructure.
However, this discontinuous substructure without active interfaces eliminates any possibility of creating a second potential barrier necessary for the increase of the voltage of the open circuit V.sub.OC and it moreover has, a higher resistivity than that of the starting material.
Moreover, the speed of local recombination within the layer of defects is very high and the electrical field of the junction P-N is not sufficient to save the photogenerated carriers of the fault region.
Thus, all the carriers in excess of the same sign are directed in the same direction relative to the interface P-N and the electrical field is applied to the substructure as an external polarization. Moreover, the length of the mean path of the photogenerated carriers in the substructure is about equal to half the thickness of the substruc
REFERENCES:
Z. Kuznicki et al., "Infrared Absorption of a New Very High Efficiency Si Solar Cell", 12th European Photovoltaic Solar Energy Conference, Apr. 11-15, 1994, vol. 1, pp. 1056-1059.
Z. Kuznicki et al., "A Method of L-H Interface Insertion for Very High Efficiency Silicon Cells", 12th European Photovoltaic Solar Energy Conference, Apr. 11-15, 1994, vol. 1. pp. 793-796.
Z. Kuznicki, "L-H Inteface Improvement for Ultra-High-Efficiency Si Solar Cells", J. Appl. Phys., vol. 74, No. 3, Aug. 1, 1993, pp. 2058-2063.
Z. Kuznicki et al., "Some Electrical Properties of a New Very High Efficiency Si Solar Cell with L-H Interfaces", 12th European Photovoltaic Solar Energy Conference, Apr. 11-15, 1994, vol. 1, pp. 552-555.
Z. Kuznicki et al., "A New L-H Interface Concept for Very High Efficiency Silicon Solar Cells", 23rd IEEE Photovoltaic Specialists Conference, May 10, 1993, pp. 327-331.
C. Summonte et al., "Spectral Behavoir of Solar Cells based on the "Junction Near Local Defect Layer" Design", Appl. Phys. Lett., vol. 3, No. 6, Aug. 9, 1993, pp. 785-787.
J. Li et al., "35% Efficient Nonconcentrating Novel Silicon Solar Cell", Appl. Phys. Lett., vol. 60, No. 18, May 4, 1992, pp. 2240-2242.
Z. Kuznicki, "Some Aspects of the Multi-Interface Structure for BSF Solar Cells", Solar Energy Materials and Solar Cells, vol. 31, 1993, pp. 383-399 .
Centre National de la Recherche Scientifique, Etablissement Publ
Chapman Mark
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