Amorphous Si solar cells with delta-doped (delta-doped) p-layer were prepared by a multichamber photochemical vapor deposition (photo-CVD) system. By optimizing the structure of the delta-doped p-layer, a conversion efficiency of 12.3% (AM1) was obtained for small-area solar cells with a delta-doped (AM1) was obtained for small-area solar cells with a delta-doped p-layer using B2H6 as a dopant source. The delta-doped p-layers deposited with trimethylboron (TMB) and triethylboron (TEB) as new boron sources were characterized. It was found that the boron layers obtained with TMB by photo-CVD contain a large amount of carbon atoms which degrade the solar cell performance. Carbon contamination was suppressed both by the plasma CVD method with a gas mixture of TMB, H2 and He and by the photo-CVD method with TEB.