Deposition of device quality amorphous silicon and solar cell from argon dilution of silane

Abstract

In our present study hydrogenated amorphous silicon (a-Si:H) thin films and solar cells have been prepared in a conventional single chamber rf-PECVD unit from silane–argon mixture by varying radio frequency (rf) power densities from 6mW/cm2 to 50mW/cm2. By optimizing the properties of the intrinsic material we have chosen a material which is deposited at 6mW/cm2 rf power density, 0.2Torr pressure, 175oC substrate temperature and by 97% argon dilution. For this material minority carriers (holes) diffusion length (Ld) measured in the as deposited state is 180nm and it degrades by 15% after light soaking. This high Ld value indicates that the material is of device quality. We have fabricated a single junction solar cell having the structure p-a-SiC:H/i-a-Si:H/n-a-Si:H without optimizing the doped layers. This set exhibits a mean open circuit voltage of 0.8V and conversion efficiency of 7.7%. After light soaking conversion efficiency decreases by 15% which demonstrates that it is possible to deposit device grade material and solar cells from silane–argon mixture.