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Targeted Search for Effective Intermediate Band Solar Cell Materials

Recent years have seen a number of candidate materials for intermediate band (IB) solar cells, but none has demonstrated a high-efficiency device. We explain this deficit by means of a figure of merit, which predicts the potential effectiveness of candidate IB materials in advance of device fabrication. This figure of merit captures in a single parameter the inherent tradeoff between enhanced absorption and enhanced recombination within an IB material, and it suggests a path toward efficient IB materials. We illustrate a screening approach based on this figure of merit for a specific class of IB material systems: a dopant-induced impurity band in silicon. We show, in this case, that the optical and nonradiative electrical trapping cross sections of impurities, widely studied properties that can be measured in bulk materials, determine the potential performance of IB solar cell devices. We conclude with a list of appealing and unappealing candidate material systems.