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 VOC in amorphous silicon based pin solar cells. We show that the modeling is consistent with measurements on the intensitydependence 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 VOC with the intrinsic layer bandgap EG. The experimental correlation for optimized cells is VOC = (EG/e)-0.79. The correlation is simply explained if VOC in these cells is determined by the intrinsic layer, and in particular by the (variable) bandgap and by a nonvarying valence bandtail width (about 48 meV) of this layer