Thermionic emission model for interface effects on the open-circuit voltage of amorphous silicon based solar cells

We present computer modeling for effects of the p/i interface upon the open-circuit voltage V_oc in amorphous silicon based pin solar cells. We show that the modeling is consistent with measurements on the intensity-dependence for the interface effect, and we present an interpretation for the modeling based on thermionic emission of electrons over the electrostatic barrier at the p/i interface. We present additional modeling of the relation of V_oc with the intrinsic layer bandgap E_G. The experimental correlation for optimized cells is V_oc = (E_G/e)-0.79. The correlation is simply explained if V_oc in these calls is determined by the intrinsic layer, and in particular by the (variable) bandgap and by a non-varying valence bandtail width (about 48 meV) of this layer.