Fabrication And Electrical Characteristics Of Doped Large Grain Polycrystalline Silicon Films

In recent years, the polycrystalline silicon (poly-Si) thin-film solar cells have attracted wide attention because of their high conversion efficiency, good stability, and low cost. The effects of minority carrier lifetime, diffusion length and surface combination velocity on the conversion efficiency of solar cell are studied by using tow-dimensional simulation software of solar cell, and indicated improved process mehtods. Large grain polycrystalline silicon thin films have been deposited on SiO2, quartz and sapphire by low pressure chemical phase deposition (LPCVD) and high frequency induction-heated chemical phase deposition (HFCVD). The effect of the substrate temperature, reactive pressure and SiH4 concentration on the growth rate and grain size of the deposited films are studied by scanning electronic microscopy (SEM) and a-step apparatus. It is found that the grain sizes of large grain polycrystalline silicon films are 1-2μm at typical experimental conditions. Doping of the films is achieved by post-diffusion and in situ-diffusion methods. The effects of doping time, doping temperature, thickness of films, different substrates, size of grains, and annealing on electrical properties of films by using four-point probe. The results indicate that higher temperature and larger grains could lead to lower sheet-resistance of films, and the lowest value is about 0.-4Ω/□; the substrate of sapphire can cause better crystallization; the defects in the films can be reduced effectively by annealing to improve the quality of films.