Theoretical analysis on the limitations of the open-circuit voltage of a hydrogenated amorphous silicon p-i-n solar cell

Abstract

We have made theoretical studies on the limitation of the open-circuit voltageV _oc of a hydrogenated amorphous silicon (a-Si:H) p-i-n type solar cell. The effects of the tail states in the a-Si:H i layer and of the interface recombination are discussed in detail. The opencircuit voltage increases when the distribution of the tail states is sharp and/or the capture cross sections of these states are small. This is because the recombination rate of photogenerated carriers and/or the density of space charge due to trapped carriers in these states become low in these conditions. These effects of the tail states on the value ofV _oc become pronounced when the built-in potential of the p-i-n junction is high. The decrease in the effective recombination velocity of carriers at the p/i and n/i interfaces results in an increase ofV _oc. This increase becomes remarkable when the effects of the tail states on the value ofV _oc are small. Both the sharp distribution of tail states and the small value of the interface recombination velocity are necessary to increase considerably the value ofV _oc. We show the conditions of the material parameters necessary to obtain an open-circuit voltage of 1.0 V.