Discrete Donor–Acceptor Pair Transitions in CH₃NH₃PbI₃ Perovskite Single Crystals

Abstract

Achieving a better understanding of the physics of defects in halide perovskites (HPs) is a key challenge for improving the efficiency of the devices. Herein, a comprehensive study of the defect emission of CH3NH3PbI3 perovskite single crystals is presented. The emission of the pristine surface of cleaved crystals is systematically investigated based on steady‐state and time‐resolved micro‐photoluminescence (micro‐PL) spectroscopy. Donor–acceptor pair (DAP) recombination is observed due to the presence of native shallow defects. The DAP spectra present an important variability depending on the location on the surface of the crystals due to inhomogeneous defect distribution. A strong blueshift of the emission is measured as a function of excitation power and is explained by fluctuating potential caused by compensated defects. With increasing photocarrier density, a transition from a structureless to a structured DAP emission with several longitudinal optical phonon replicas is observed. The DAP transition is characterized by the redshift of the emission with time and a slow, non‐exponential PL decay. Sharp discrete lines with sub‐meV widths, the most recognizable spectral signature of DAP transition, are revealed. Herein, the apparently contradictory previous observations on defect emission of CH3NH3PbI3 are reconciled by the results and new insights are provided into the properties of defects in HPs.

Free Exciton and Defect-Related States in CH3NH3PbCl3 Perovskite Single Crystal

“…A slight blue shift is typical for the local heating of the sample. Recombination on DAP was observed in MAPbI 3 with strong blueshift, owing to potential fluctuations, which testifies to the high level of compensation. Although DFT calculations predict a high density of Frenkel defects (chlorine vacancies V Cl and Cl – interstitials) in MAPbCl 3 taking into account the results of power dependence measurements, there is a possibility of a high impact of uncompensated defects emerging during crystal growth.…”