The relation of dark and illuminated diode parameters to the open-circuit voltage of amorphous silicon p-i-n solar cells

We have measured the current-voltage characteristics of a-Si:H p-i-n solar cells having open-circuit voltages (Voc) between 0.70 and 0.90 V as a function of temperature and light intensity. The diode parameters (diode factor, saturation current density, and built-in voltage) were calculated in the light and in the dark. We find that parameters obtained in the dark have no relevance to the analysis of Voc, but they do indicate that tunneling may be a significant effect in the dark. The Voc is dominated by recombination at the p/i interface or in the i layer near this interface. Reducing interface recombination with a carbon buffer layer and reducing bulk recombination with less i layer impurities improves Voc by reducing the forward recombination current density.