Nanometer-Resolved Mapping of Organic Cation Migration Behavior in Methylammonium Lead Halide Perovskites

The performance and stability of organic metal halide perovskite (OMHP) optoelectronic devices have been associated with ion migration. Understanding of nanoscale resolved organic cation migration mechanism would facilitate structure engineering and commercialization of OMHP. Here, we report a three-dimensional approach for in situ nanoscale infrared imaging of organic ion migration behavior in OMHPs, enabling to distinguish migrations along grain boundary and in crystal lattice. Our results reveal that organic cation migration along OMHP film surface and grain boundaries (GBs) occurs at lower biases than in crystal lattice. We visualize the transition of organic cation migration channels from GBs to volume upon increasing electric field. The temporal resolved results demonstrate the fast MA+ migration kinetics at GBs, which is comparable to diffusivity of halide ions. Our findings help understand the role of organic cations in the performance of OMHP devices, and the proposed approach holds broad applicability for revealing migration mechanisms of organic ions in OMHPs based optoelectronic devices. Combining with the surface sensitive heterodyne mode and volume sensitive homodyne mode of infrared photo induced force microscopy, the 3-dimensional organic ion migration behaviors in organic metal halide perovskite has been imaged with sub-10 nm resolution, revealing the bias-dependent transition of MA+ migration channels from grain boundaries to grains and allowing the calculation of MA+ drift velocity across GBs. image