Photoluminescence properties of a-Si:H based thin films and corresponding solar cells

Amorphous hydrogenated silicon (a-Si:H) is a well-known semiconductor with metastable properties. Direct surface exposure, as it occurs e.g. in rf plasma equipments, introduces damage due to the charged particle bombardment. The paper deals with photoluminiscence properties of virgin, oxide layer covered and chemically treated (in KCN solutions) surfaces of a-Si:H and correspondingsolarcell structures. The cyanide treatment improves the electrical characteristics of MOS structures as well as solarcells. X-ray diffraction at grazing incidence and reflectance spectroscopy complete the study. The photoluminescence measurements were performed at liquid helium temperatures at 6 K using an Ar laser and lock-in signal recording device containing the PbS and Ge photodetectors. Photoluminescence bands were observed as broad luminescent peaks between 1.05–1.7 eV. Two new peaks were detected at 1.38 and 1.42 eV. The evolution of the band at ∼1.2 eV related to microcrystalline silicon is investigated. The fitting and simulation of photoluminiscence spectra are presented. The surface luminescent properties of a-Si:H based structures (double layers, single thinfilmsolarcells) before and after the passivation are compared with those of very thin oxide layers and chemically treated surfaces.