Electrical Confinement for the Crystalline Silicon Thin-Film Solar Cell on Foreign Substrate

Crystalline silicon thin-film solar cells have the potential to drastically reduce the cost for silicon solar cells. The aim of the work described in this book was to improve the quality of thin silicon layers on foreign substrates and to apply the experience gained hereby to various low-cost substrates. Two aspects of the crystalline silicon thin-film solar cell were examined intensively to reach this goal: diffusion barrier properties of common intermediate layers, and zone-melting recrystallisation of silicon layers. For investigation of diffusion barrier layers, the focus was set to diffusion of the transition metals iron, chromium and vanadium in the intermediate layer materials SiO2 and SiNx deposited by plasma-enhanced chemical vapour deposition. Temperatures ranging from 900C to 1350C were applied to the samples. Zone-melting recrystallisation of silicon is an important technique to prepare large crystal grains of several millimetres width and several centimetres length on amorphous substrates. Parameter studies on SiO2-capped multicrystalline silicon wafers were done to investigate the effect of the so-called supercooled zone on crystal quality. One-side contacted solar cells were prepared on optimised layers on such model substrates. For the first time, also low-cost ribbon silicon and ceramics (SiSiC, Si3N4, SiAlON, mullite) were tested as substrate material. Cell efficiencies up to 10.5% could be obtained when using these materials. The author: Dr. Stefan Reber studied Physics at the Technical University of Darmstadt, Germany. He joined the solar cell department of the Fraunhofer Institute for Solar Energy Systems for his Ph.D. thesis, where he was in charge of improving crystalline silicon thin-film solar cells on foreign substrates.