Elucidating the Role of Ion Migration and Band Bending in Perovskite Solar Cell Function at Grain Boundaries via Multimodal Nanoscale Mapping

Abstract Although hybrid organic–inorganic halide perovskite solar cells have achieved extraordinary improvements over the past few years, questions remain about the role of grain boundaries. This article reports on the nanoscale point‐by‐point current–voltage mapping of photovoltaic characteristics in inverted methylammonium lead triiodide perovskite solar cells. These measurements reveal an increased open‐circuit voltage and shunt resistance, along with a suppressed short‐circuit photocurrent at grain boundaries and nearby regions. Support from nanoscale ionic strain and surface potential mapping suggests that local ion accumulation and downward band bending can facilitate charge separation, but hinder charge collection at grain boundaries.