Spatially-resolved nanoscale measurements of grain boundary enhanced photocurrent in inorganic CsPbBr3 perovskite films

The main hindrances which preclude the commercial application of hybrid organic-inorganic halide perovskite solar cells is their thermodynamic instability and fast environmental degradation. Fully inorganic halide perovskites are still far from the MAPbI(3) record power conversion efficiency, but they are significantly more stable. In this work, a significant current increase in the absorbing CsPbBr3 halide perovskite layer is measured by conductive Scanning Probe Microscopy (c-SPM) after thermal ageing without visible structural degradation. Enhanced local photocurrent along grain boundaries and triple junctions is observed by c-SPM. These effects are accompanied by the appearance of downward band bending along grain boundaries as measured by Kelvin Probe Force Microscopy. It is suggested that the resulting built in electric field effectively acts to facilitate splitting of photogenerated electron-hole pairs at grain boundaries by attracting electrons and repelling holes. The fact of current increase, even though significantly smaller in amplitude, is further confirmed by macroscopic measurements on a complete cell, which may arise from improvement of the ITO/PEDOT:PSS/CsPbBr3 interfaces upon thermal ageing. These measurements provide advanced understanding of how nanoscale localized structure and function evolve in time and upon thermal ageing. These findings proved further impetus for increasing inorganic halide perovskites power conversion efficiency up to levels sufficient for practical applications.