Investigation of the Interactions Between Photo-Generated Charge Carriers and Defects in Perovskite Solar Cells by Photoluminescence Spectroscopy

In perovskite solar cells, the interactions between photo-generated charge carriers (electrons and holes) and the various defects such as vacancies, interstitials, and surface defects not only affect the power conversion efficiency of the solar cells, but also lead to device stability issues such as current-voltage (J-V) hysteresis and photodegradation. In this study, steady-state and time-resolved photoluminescence (PL) spectroscopies are adopted to investigate these interactions in both organometal halide perovskite thin films and photovoltaic devices. We observe the PL intensity of methylammonium lead iodide (MAPbI₃) film in a solar cell show hysteretic responses when changing the voltage scanning direction, namely PL-V hysteresis. Our study reveals that the motion of the charged defects (e.g., ionic vacancies) driven by the external electric field not only lead to J-V hysteresis, but also changes the distribution and density of charge traps that are responsible for nonradiative recombination. Spatially resolved PL of MAPbI₃ films in planar heterojunction solar cells are probed by time-resolved confocal microscopy. We observe significant different PL-V hysteresis behavior in the film region close to an interface comparing to the area away from the interface. This work sheds a light on interface effect on the correlation between charge extraction and the hysteretic characteristics of perovskite solar cells.