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Thin film solar cells often have high densities of dopants and native defects that result in carrier compensation and local electrostatic fields, which produce band edge fluctuations observable as tails in luminescence and absorption spectra. The analysis here shows that these fluctuations can reduce the open-circuit voltage (Voc) by tens to hundreds of millivolts and alter the Voc temperature coefficients. Although the extrapolation of Voc to 0 K is often used to gauge interface recombination, reductions in this value can also be explained by band edge fluctuations. In addition, these fluctuations can explain pronounced anomalous trends between carrier concentration and Voc in state-of-the-art CdSeTe:As solar cells, representing a significant departure from device models that do not include them. The analysis can be applied to other thin film technologies. To improve CdSeTe solar cell performance, it is critical to assess band edge fluctuations and address carrier compensation and defect chemistry to mitigate their impact.
Rosenblatt et al. (Fri,) studied this question.