Origin and whereabouts of recombination in perovskite solar cells

The success of metal halide perovskite solar cells stems from high absorption combined with a low recombination rate. Despite the fact these properties are inherent to the perovskite material, the choice of selective contacts is critical to achieve high voltages according to experimental evidence. In this work, the impedance and the open-circuit photopotential are measured for two excitation wavelengths (blue and red light), in two illumination directions (back and front), and at different temperatures. The open-circuit recombination characteristics of two different perovskite compositions, i.e., pure MAPbI₃ and mixed ion-based (FAPbI₃)_0.85(MABr₃)_0.15, and with two different hole selective layers (Spiro-OMeTAD and P3HT) have been studied. Our results indicate that, for the studied devices, the recombination process that determines the open-circuit potential is governed by the bulk of the perovskite layer via a trap-limited mechanism, but surface-mediated recombination cannot be ruled out for P3HT contact or degraded devices. Further, we propose a model that provides a general interpretation of the nature of recombination in perovskite solar cells.