Observation of Grain Boundary Passivation and Charge Distribution in Perovskite Films Improved with Anti-solvent Treatment

Owing to the polycrystalline nature of hybrid perovskite thin films, the trap states in grain boundaries (GBs) introduced by charged defects play an important role in determining the charge collection efficiency and have a significant impact on their optoelectronic properties. Herein, we show the direct imaging of the GB passivation of perovskite films through an anti-solvent treatment and the anomalous charge distribution across the films due to the passivation. The downward band bending at the GBs has been observed at nanometer scale using Kelvin probe force microscopy. This revealed that a hot chlorobenzene treatment decreases the band bending at GBs and allows more homogeneous electronic properties throughout the film after passivation. Conductive atomic force microscopy has been employed to show the charge transport mapping across the films. It was found that the passivation effect not only changes the surface potential at GBs but also enhances the overall charge collection efficiency of the film. Our work provides a solution to reduce the density of charge defects at GBs through hot anti-solvent treatment, which is demonstrated to be a promising strategy to decrease the recombination losses at GBs and, thereby, increase the electronic quality of the perovskite films as well as enhance the device performance.