Preparation of undoped and doped microcrystalline silicon(μc-Si:H) by VHF-GD for p-i-n solar cells

The electronic transport properties of μc-Si:H materials were investigated. The μc-Si:H was deposited by the very high frequency-glow discharge (VHF-GD) technique at an RF-excitation of 70 MHz. Very thin <p> doped layers (100-400 Å) were studied. Conductivities higher than 10-3 (Ω cm)^-1 could be achieved for films thicker than 150 Å. The as-deposited μc-Si:H is a slightly <n>-type material and compensation was obtained by μ-doping with boron. Light-induced degradation of the compensated film showed better stability than for a-Si:H. Entirely μc-Si:H p-i-n solar cells were prepared by incorporating the compensated layer in the structure. The μc-Si:H cells show indeed an increase in the spectral response beyond 750 nm compared to amorphous silicon solar cells. These results indicate that the slightly doped μc-Si:H is a new promising photovoltaically active material, which merits closer investigation.