Chemical stability and performance of doped silicon oxide layers for use in thin film silicon solar cells

Doped hydrogenated silicon oxide layers (SiO
_x
:H) have recently successfully been integrated as front window layer, back reflector layer, intermediate reflector layer, passivation layer and junction layer in thin film silicon solar cells. Depending on the deposition conditions of the SiO
_x
: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 the p-type doped (p-)SiO
_x
:H is responsible for this degradation. The degradation of p-SiO
_x
:H is caused by the in-diffusion of foreign molecules from the ambient air. Stable p-SiO
_x
: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. Such encapsulation can be achieved by a dense n-type (n-)SiO
_x
:H in the back reflector of the cell.