Chemical Stability and Performance of Doped Silicon Oxide Layers for Use in Thin-Film Silicon Solar Cells

Doped hydrogenated silicon oxide layers (SiOX:H) have recently been successfully integrated as front window layers, back reflector layers, intermediate reflector layers, passivation layers, and junction layers in thin-film silicon solar cells. Depending on the deposition conditions of the SiOX:H layers, some devices suffer from a degradation in performance in time. In this paper, we demonstrate the responsible mechanism involved. It is demonstrated that oxidation of the p-type doped (p-)SiOX:H with a high crystallinity and, therefore, poor passivation of crystalline grains is responsible for this degradation. The oxidation of p-SiOX:H is caused by the in-diffusion of water vapor from the ambient air. Stable p-SiOX:H can be obtained if the material is processed at higher pressure. In addition, the degradation can be prevented if the cell is well encapsulated, like using dense n-type (n-)SiOX:H in the back reflector of the cell.