Unraveling the hysteretic behavior at double cations-double halides perovskite - electrode interfaces

Despite over a decade of research on metal halide perovskites (MHPs) in the context of photovoltaic applications, understanding the nature of electronic and ionic processes associated with current-voltage (I-V) hysteretic behavior has been limited. Here, we explore the hysteretic behavior in (FAPbI₃)_0.85(MAPbBr₃)_0.15 perovskite devices with lateral Cr electrodes by applying first order reversal curve (FORC) bias waveform in I-V, Kelvin probe force microscopy (KPFM) measurements, and in-situ chemical imaging by time-resolved time-of-flight secondary ion mass spectrometry (tr-ToF-SIMS). In dark, we reveal pronounced hysteretic behaviors of charge dynamics in the off-field by probing time-dependent current and contact potential difference (CPD). Under illumination, transient and hysteretic behaviors are significantly reduced. The tr-ToF-SIMS results reveal that the hysteretic behaviors are strongly associated with accumulation of Br^- ions at the interfaces. In addition, the low mobility MA⁺ ions result in transient behavior and contribute to the hysteretic phenomena. It was shown that Pb²⁺ ions can be reduced at the interfaces due to electrochemical reactions with the electrode in the presence of charge injection and photogenerated charges. These hysteretic behaviors associated with charge dynamics, ion migration, and interfacial electrochemical reaction are critical to further improve the performance and stability of MHPs photovoltaics and optoelectronics.