Photovoltaic Properties of a-Si:H Films Grown by Plasma Enhanced Chemical Vapor Deposition: A Review

Amorphous silicon films are currently receiving a worldwide renewed and intense research and commercial focus for low-cost solar power generation. In this article we review the history and current status of hydrogenated amorphous silicon films (a-Si:H) for thin film photovoltaics, and the role of intrinsic a-Si:H films in heterojunction (a-Si:H/c-Si) solar cells. The focus of this article is on plasma enhanced chemical vapor deposition (PECVD) of these films from silane (SiH4). Very high frequency (VHF) PECVD deposition and its limitations are discussed. Properties and requirements of intrinsic and doped a-Si:H films are presented. Light-induced degradation of a-Si:H films are reviewed in detail. Current status of single junction a-Si:H solar cells and factors influencing cell performance are also discussed. Since the efficiency and stability of thin film a-Si:H solar cells are low, a-Si:H films can be successfully used in other solar cell technologies such as c-Si based back heterojunction solar cells, where doped a-Si:H films are used at the rear side of the substrate for emitter and back surface field.