Boron-doped amorphous diamondlike carbon as a new p-type window material in amorphous silicon p-i-n solar cells

Abstract

A boron-doped hydrogenated amorphous diamondlike carbon (a-DLC:H) was prepared using a mercury-sensitized photochemical vapor deposition (photo-CVD) method. The source gases were B2H6 and C2H4. By increasing the boron doping ratio (B2H6/C2H4) from 0 to 12 000 ppm, the dark conductivity increased from ∼10−9 to ∼10−7 S/cm. A boron-doped a-DLC:H with an energy band gap of 3.8 eV and a dark conductivity of 1.3×10−8 S/cm was obtained at a doping ratio of 3600 ppm. By using this film, amorphous silicon (a-Si) solar cells with a novel p-a-DLC:H/p-a-SiC double p-layer structure were fabricated using the photo-CVD method and the cell photovoltaic characteristics were investigated as a function of a-DLC:H layer thickness. The open circuit voltage increased from 0.766 V for the conventional cell with a 40-Å-thick p-a-SiC to 0.865 V for the cell with a p-a-DLC:H (15 Å)/p-a-SiC (40 Å) double p-layer structure. The thin (<15 Å) p-a-DLC:H layer proved to be an excellent hole emitter as a wide band gap window layer.