Microcrystalline B-doped window layers prepared near amorphous to microcrystalline transition by HWCVD and its application in amorphous silicon solar cells

The electronic and structural properties of p-type microcrystalline silicon films prepared near the microcrystalline to amorphous (μc-amorphous) transition by hot-wire chemical vapor deposition are studied. Silane is used as a source gas while H2 as diluent and trimethylboron (TMB) and boron trifluoride (BF3) as doping gases. Increasing TMB concentration from 0.01% to 5% favors the amorphous growth whereas for BF3 the crystalline fraction remains constant. The dark conductivity (σd) of μc-Si:H p-layers remains approximately constant for TMB = 1–5% at constant crystalline fraction Xc. This dark conductivity behavior is attributed to the decrease in doping efficiency with increasing TMB concentration. The best initial efficiency obtained for a 400 nm amorphous pin solar cell with optimized μc-Si:H p-layer is 7.7% (Voc = 874 mV, Jsc = 12.91 mA/cm2, FF = 68%).