On the prospect of CZTSSe-based thin film solar cells for indoor photovoltaic applications: A simulation study

In this work we present the first systematic study on the prospect of Cu2ZnSn(S,Se)4 or CZTSSe-based thin film photovoltaic devices for indoor energy harvesting applications. Based on numerical analysis, we estimate the performance characteristics of the experimentally reported highest-efficiency CZTSSe device when it is operated under a commercially available white light emitting diode (LED). The obtained efficiency of 13.77% and fill factor of 71.05% are both higher than the values reported under AM1.5 solar radiation. The results of our analysis indicate that performance enhancement under indoor condition arises from the enhanced short-circuit current at high intensity and open-circuit voltage at low intensity, which are both related to the high photon yield of the indoor spectrum corresponding to the bandgap of CZTSSe. Further performance enhancement under indoor condition can be achieved using a type-II band alignment, which we have designed and analyzed employing an intrinsic ZnO layer. The enhanced charge separation resulting from built-in-field of the ZnO layer increases the open circuit voltage by as much as 0.17 V, which in effect leads to an overall efficiency of 15.85% when operated under the considered white LED spectrum.