Photovoltaic performance of a-Si:H homojunction p-i-n solar cells: A computer simulation study

Abstract

A first principles computer model for simulating the performance of amorphous semiconductor solar cells has been developed. With a suitable choice of parameters, the calculated results for the illuminated J-V characteristics and solar cell quantum efficiencies are shown to agree well with experiments. The model has been used in this paper to study the sensitivity of the light J-V characteristics to various device and material parameters in p-i-n homojunction solar cells. The single most important factor controlling the open circuit voltage, short circuit current, fill factor, and cell efficiency is the transparent conducting oxide/p-a-Si:H contact barrier height φbo, when φbo is less than a certain critical value. Also shown is that practically no improvement in cell performance can be achieved by decreasing the dangling-bond midgap state density, described by Gaussian distribution functions, to lower than 1016 cm-3, unless the valence-band tail states are also reduced. Moreover, results indicate that light-induced defect states have neutral capture cross sections of 10 -15 cm2, which is at least one order of magnitude higher than the corresponding quantity for the gap states in annealed materials. Finally, low band microscopic carrier mobilities are found to have a strong detrimental influence on solar cell performance.