The effect of surface states at the SnO2/p-a-Si:H interface

A one-dimensional photovoltaic cell simulation has been used to model a SnO2/p-a-Si:H interface, in thermodynamic equilibrium. Central to the study is the effect that acceptor-like surface states in the p-a-Si:H have on the contact potential at this interface. Such surface states were assumed to have a Gaussian distribution. It was found that in order to maintain a constant negative contact potential in the p-layer, the surface state concentration needed to be increased as the distribution was shifted towards the conduction band edge. It was found that, for a given surface state concentration, the contact potential became more negative as the distribution was shifted towards the conduction band edge. It was also found that, when the surface states were located at a fixed position in the gap, increasing their concentration resulted in a decrease in the magnitude of the contact potential, with the contact potential eventually becoming positive for large concentrations. Increases in the dopant concentration also caused the contact potential to become more negative.