Solar cells amorphous

In the case of using a-SiC H as window material in p-i-n amorphous solar cells this will not only reduce the interface reflections and surface absorptions of incident light, but also greatly improve the transmissivity of the p layer in the solar cells. By introducing a microcrystalline phase into a-SiC to obtain the higher doping efficiency, the efficiency of the solar cells can be increased further [17]. 

Devices based on a-SiC H have certain advantages over other semiconductor materials in a number of applications in optoelectronics, such as thin-film light-emitting diodes, coatings for laser facets, and a broadband window material for amorphous solar cells [163-165], These applications exploit the fact that the optical energy gap and the refractive index of the films can be varied by changing their chemical composition. 

Amorphous solar cells are usually p-i-n structures with high doping levels in the p and n regions and the i-region optimized for higher mobihty and low gap state... 

Germane is used, along with silane, SiH, to make amorphous or crystalline siUcon solar cells having an extended solar energy absorption range to increase conversion efficiency. 

Good solar cell results have been obtained from cells of materials, including polycrystaUine silicon, amorphous silicon—hydrogen (a-Si H) alloys, Cu S—CdS, CuInSe2—CdS, and CdTe. 

In most cases, CVD reactions are activated thermally, but in some cases, notably in exothermic chemical transport reactions, the substrate temperature is held below that of the feed material to obtain deposition. Other means of activation are available (7), eg, deposition at lower substrate temperatures is obtained by electric-discharge plasma activation. In some cases, unique materials are produced by plasma-assisted CVD (PACVD), such as amorphous siHcon from silane where 10—35 mol % hydrogen remains bonded in the soHd deposit. Except for the problem of large amounts of energy consumption in its formation, this material is of interest for thin-film solar cells. Passivating films of Si02 or Si02 Si N deposited by PACVD are of interest in the semiconductor industry (see Semiconductors). 

Fig. 4. Some electronic device applications using amorphous silicon (a) solar cell, (b) thin-fiLm transistor, (c) image sensor, and (d) nuclear particle detector.

In many cases, the deposited material can retain some of the original chemical constituents, such as hydrogen in siUcon from the deposition from silane, or chlorine in tungsten from the deposition from WCl. This can be beneficial or detrimental. For example, the retention of hydrogen in siUcon allows the deposition of amorphous siUcon, a-Si H, which is used in solar cells, but the retention of chlorine in tungsten is detrimental to subsequent fusion welding of the tungsten. 

Schropp, R.E.l. and Zeeman, M. (1998) Amorphous and Microcrystalline Silicon Solar Cells (Kluwer Academic Publishers, Dordrecht). 

Limitations of Plasma CVD. With plasma CVD, it is difficult to obtain a deposit of pure material. In most cases, desorption of by-products and other gases is incomplete because of the low temperature and these gases, particularly hydrogen, remain as inclusions in the deposit. Moreover, in the case of compounds, such as nitrides, oxides, carbides, or silicides, stoichiometry is rarely achieved. This is generally detrimental since it alters the physical properties and reduces the resistance to chemical etching and radiation attack. However in some cases, it is advantageous for instance, amorphous silicon used in solar cells has improved optoelectronic properties if hydrogen is present (see Ch. 15). 

Cost must be reduced considerably before solar cells of amorphous silicon could be considered for large-... 

Delahoy, A., Doele, B., Ellis, F., Ramaprasad, K., Tonon, T., and Van Dine, J., Amorphous Silicon Films and Solar Cells Prepared by Mercury-Sensitized Photo-CVD of Silane and Disilane, Materials Issues in Applications of Amorphous Silicon Technology, (D. Adler, et al., eds), MRS Proc., (49) 33-39 (1985)... 

Delahoy, A. E., Recent Developments in Amorphous Silicon Photovoltaic Research and Manufacturing at Chronar Corporation, Solar Cells, (27) 39-57 (1989)... 

Gordon, R. G, Proscia, J., Ellis, F., and Delahoy, A., Texture Tin Oxide Films Produced by Atmospheric Pressure Chemical Vapor Deposition from Tetramethyltin and Their Usefulness in Producing Light Trapping in Thin Film Amorphous Silicon Solar Cells, >/or Energy Materials, (18) 263-281 (1989)... 

We have already mentioned amorphous silicon solar cells. New processes have been developed to manufacture solar cells based upon deposition of very thin films of photosensitive materials. Such processes have a distinct cost advantage since once the films are deposited, little further processing is needed to form the final solar cell module. 

Schropp and Zeman [11] have classified current production systems for amorphous silicon solar cells. They argue that cost-effective production of solar cells on a large scale requires that the product of the deposition time needed per square meter and the depreciation and maintenance costs of the system be small. Low... 

Deposition of hydrogenated amorphous silicon employing the VHF PECVD technique (typical frequency range 20-110 MHz) has been reported to yield an increase in deposition rate by one order of magnitude over the conventionally used frequency of 13.56 MHz [16,146,250,280], without adversely affecting material quality [183, 280, 475]. This is of great importance for lowering the production cost of fl-Si H solar cells. 

FIG. 72. Schematic cross-section of (a) a single junction p-i-n o-Si H superstrata solar cell and (b) a tandem solar cell structure. (From R. E. I, Schropp and M. Zeman. "Amorphous and Microcrystalline Silicon Solar Cells—Modeling, Materials and Device Technology," Kluwer Academic Publishers, Boston, 1998, with permission.)... 

R. E. I. Schropp and M. Zeman, Amorphous and Microcrystalline Silicon Solar Cells—Modeling, Materials and Device Technology. Kluwer Academic Publishers, Boston, 1998. 

A. H. Mahan and M, Vanecek, Amorphous Silicon Materials and Solar Cells," AIP Conference Proceedings, Vol. 234 (B. Stafford, Ed.), p. 195. American Institute of Physics, New York, 1991. 

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