The electronic and structural properties of p-type microcrystalline silicon films prepared near the microcrystalline to amorphous (mu c-amorphous) transition by hot-wire chemical vapor deposition are studied. Silane is used as a source gas while H-2 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 (sigma(d)) of mu c-Si:H p-layers remains approximately constant for TMB=1-5% at constant crystalline fraction X-c. 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 mu c-Si:H p-layer is 7.7% (V-oc = 874 mV, J(sc) = 12.91 mA/cm(2), FF = 68%). (c) 2005 Elsevier B.V. All rights reserved.