Intrinsic Microcrystalline Silicon Thin Films Prepared by Hot-Wire Cell Method and Their Application to Solar Cells

Abstract

Microcrystalline silicon (µc-Si:H) thin films and solar cells were prepared by a hot-wire cell (HW-cell) method. A maximum conversion efficiency of 6.0% (Voc: 0.50 V, Jsc: 19.69 mA/cm2, F.F.: 0.61, active area: 0.086 cm2, AM1.5) was obtained for µc-Si:H solar cells prepared at a low filament temperature of 1800°C. The influence of filament temperature on µc-Si:H film properties was investigated. As a result, it was found from secondary ion mass spectroscopy (SIMS) results that tungsten (W) and aluminum (Al) concentrations largely increase with increasing filament temperature from 1800°C to 2100°C. Next, we found that a considerable degradation of solar cell performances occurs with aging. The degradation of intrinsic µc-Si:H absorber layers with aging was investigated, and it was found that the peak at 1000–1100 cm-1 originating from Si–O–Si bonds and spin density markedly increase. SIMS results also showed that O and C atoms in our µc-Si:H films are as low as 2×1018 cm-3 in the initial state and the films can easily undergo post oxidation. However, it was also found that a deposition at a high substrate temperature of more than 165°C is very effective in realizing high-stability µc-Si:H films and that a 3-µm-thick a-Si:H cap layer can prevent post oxidation.