Comprehensive Elucidation of Grain Boundary Behavior in All‐Inorganic Halide Perovskites by Scanning Probe Microscopy

Abstract

AbstractAll‐inorganic halide perovskite (AIHP) is becoming one of the most promising generation materials of perovskite photovoltaics for commercialization due to its thermodynamic stability and soared efficiency. Depending on material properties, grain boundary (GB) has detrimental or beneficial effect on device photovoltaic performance. However, less attention is paid to GB behavior in AIHPs. Herein, it is concluded that the microscopic GBs are the major sites for photocarrier generation and transport, as well as the ionic pathway dominating the current hysteresis behavior in AIHP solar cells. Kelvin probe force microscopy (KPFM) measurements reveal a lower surface potential at GBs as compared to grain interiors (GIs), suggesting a significant upward band bending around GBs. Conductive atomic force microscopy (c‐AFM) measurements show a higher current flow in the vicinity of GBs, indicating enhanced carrier separation and collection taking place at GBs. Furthermore, the existence of ion motion is evidenced both by the single‐point c‐AFM measurement and voltage‐controlled KPFM measurement, which accounts for the common current hysteresis behavior in AIHP solar cells. These investigations provide an advanced understanding of the role of GBs in AIHP and further inspiration on how to optimize device performance up to the levels of organic–inorganic hybrid perovskite.