How Polarization Switch Influences Both Charge Separation and Carrier Recombination in Hybrid Perovskites

Polarization, charge localization, and electron-hole recombination are common processes in hybrid organic-inorganic perovskites. By investigating the combined effect of both organic polarization due to CH3NH3 (MA) molecular orientation and inorganic polarization due to electronegativity difference between different halides in pure MAPbBr3 perovskite and halide-mixed phase (MAPbBr1.5Cl1.5, MAPbI1.5Br1.5, MAPbI1.5Cl1.5), we demonstrate that the polarization strongly influences the charge localization and carrier recombination. The inorganic polarization plays a dominant role in localizing the valence band maximum (VBM) of ferroelectric (FE) systems, while the organic polarization dominates the localized VBM of antiferroelectric (AFE) systems. And the two polarizations compete in halide-mixed AFE structures. Particularly, it shows a compensated effect in MAPbI1.5Br1.5, which results in a fully delocalized hole distribution. Such polarization-driven charge separation would influence the nonradiative electron-hole recombination. Moreover, the applied forward and reverse biases in the actual operation of perovskite solar cells would introduce polarization switch that further changes the charge separation. As a result, the quantum coherence loss can be strongly affected during the polarization switch process, which rationalizes the long carrier lifetime in halide-mixed perovskites. This work provides new insights for optimizing carrier localization to enhance solar cell efficiency.