Hydrogen annealed ZnO:B film grown by LPCVD technique as TCO for enhancing conversion efficiency of a-Si:H/μc-Si:H tandem solar cells

Abstract

The ZnO:B (BZO) films with different boron doping levels have been prepared by low pressure chemical vapor deposition (LPCVD) technique. The electrical and optical properties of the BZO films have been systematically investigated through a post annealing treatment in hydrogen atmosphere, as well as in vacuum for comparison. It is found that conductivity of BZO films, especially with a low boron doping level, can be enhanced significantly after annealing in hydrogen, and moreover, the total transmittance (TT) and haze factor of the H2-annealed BZO films were still almost unchanged simultaneously, which were attributed to phenomena of an increase in carrier mobility with an almost constant of free carrier concentration. The conversion efficiency of a-Si:H/μc-Si:H tandem solar cell incorporating H2-annealed lowly doped BZO film as front electrode was confirmed to be improved remarkably by 1.10% due to the enhancement of TT and haze factor, as compared to that using an as-grown heavily doped BZO film as front electrode. The results indicate that H2-annealing is a quite attractive and alternative technique to optimize properties of BZO film as TCO for further enhancing conversion efficiency of a-Si:H/μc-Si:H tandem solar cells.