Thin-film polycrystalline Si solar cells on foreign substrates:: film formation at intermediate temperatures (700-1300 °C)

We give an overview and analysis of research on thin-film polycrystalline Si solar cells on foreign substrates, with layers formed at intermediate temperatures (700-1300 degreesC), covering substrates, deposition techniques and solar cell processing. The main deposition techniques that have been investigated are solution growth (SG) and chemical vapour deposition (CVD). Insufficient nucleation on foreign substrates is an important problem with SG, which could be solved with appropriate surface preparation techniques and growth conditions. With CVD, continuous layers are achieved routinely, but the electronic quality of the material is usually very low. Solar cell performance appears to be limited by a very large recombination activity of grain boundaries. Improvement can be achieved reducing the grain boundary density and recombination activity, and experimental examples are given. Devices have been demonstrated with efficiencies up to 5.5%.