Thin-film polycrystalline-silicon solar cells on high-temperature glass based on aluminum-induced crystallization of amo
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0910-A26-04
Thin-film polycrystalline-silicon solar cells on high-temperature glass based on aluminuminduced crystallization of amorphous silicon Dries Van Gestel1, Ivan Gordon1, Lode Carnel1, Linda R. Pinckney2, Alexandre Mayolet2, Jan D'Haen3, Guy Beaucarne1, and Jef Poortmans1 1 IMEC VZW, Kapeldreef 75, B-3001 Leuven, Belgium 2 Corning Inc., SP-FR, Corning, NY, 14830 3 Hasselt University, Institute for Materials Research, Wetenschapspark 1, B-3590 Diepenbeek, Belgium ABSTRACT Efficient thin-film polycrystalline-silicon (pc-Si) solar cells on foreign substrates could lower the price of photovoltaic electricity. Aluminum-induced crystallization (AIC) of amorphous silicon (a-Si) followed by epitaxial thickening at high temperatures seems a good way to obtain efficient pc-Si solar cells. Due to its transparency and low cost, glass is well suited as substrate for pc-Si cells. However, most glass substrates do not withstand temperatures around 1000°C that are needed for high-temperature epitaxial growth. In this paper we investigate the use of experimental transparent glass-ceramics with high strain-point temperatures as substrates for pc-Si solar cells. AIC seed layers made on these substrates showed in-plane grain sizes up to 16 µm. Columnar growth was observed on these seed layers during high-temperature epitaxy. First pc-Si solar cells made on glass-ceramic substrates in substrate configuration showed efficiencies up to 4.5%, fill factors up to 75% and open-circuit voltage (Voc) values up to 536 mV. This is the highest Voc reported for pc-Si thin-film solar cells on glass and the best cell efficiency reported for cells made by AIC on glass. INTRODUCTION Efficient thin-film polycrystalline-silicon (defined here as having a grain size between 0.1 and 100 µm) solar cells could lead to a large cost reduction in photovoltaics, since these cells combine the use of a limited amount of silicon with the use of inexpensive foreign substrates. Because of its transparency and low cost, glass is very suitable as substrate for this type of solar cell. Direct deposition of the pc-Si absorber layers onto glass substrates results in fine-grained Si with a high grain boundary density. To achieve larger grains with low aspect ratio, several approaches have been used. By laser crystallization, pc-Si solar cells with grains up to 100 µm were achieved on low-cost glass substrates that showed open-circuit voltages up to 510 mV [1]. By using solid phase crystallization, pc-Si cells with efficiencies of more than 8% and opencircuit voltages around 500 mV were realized on borosilicate glass [2]. We achieved large-grained pc-Si absorber layers on ceramic alumina substrates by using aluminum-induced crystallization of amorphous silicon (AIC) in combination with hightemperature silicon epitaxy [3]. In our process, thin but large-grained AIC layers serve as seed layers on top of which the absorber layers are grown at temperatures above 1000°C. So far, we reached energy conversion efficiencies of around 6% on alumina substrates. Alumina substra
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