The Role of Grain Boundaries on Ionic Defect Migration in Metal Halide Perovskites

• Published in: Advanced energy materials Vol. 10; no. 20
• Main Authors: Phung, Nga, Al‐Ashouri, Amran, Meloni, Simone, Mattoni, Alessandro, Albrecht, Steve, Unger, Eva L., Merdasa, Aboma, Abate, Antonio
• Format: Journal Article
• Language: English
• Published: 01.05.2020
• Subjects: grain boundaries; halide perovskites; ion migration; molecular dynamic simulations; photoluminescence
• ISSN: 1614-6832; 1614-6840
• DOI: 10.1002/aenm.201903735

Halide perovskites are emerging as revolutionary materials for optoelectronics. Their ionic nature and the presence of mobile ionic defects within the crystal structure have a dramatic influence on the operation of thin‐film devices such as solar cells, light‐emitting diodes, and transistors. Thin films are often polycrystalline and it is still under debate how grain boundaries affect the migration of ions and corresponding ionic defects. Laser excitation during photoluminescence (PL) microscopy experiments leads to formation and subsequent migration of ionic defects, which affects the dynamics of charge carrier recombination. From the microscopic observation of lateral PL distribution, the change in the distribution of ionic defects over time can be inferred. Resolving the PL dynamics in time and space of single crystals and thin films with different grain sizes thus, provides crucial information about the influence of grain boundaries on the ionic defect movement. In conjunction with experimental observations, atomistic simulations show that defects are trapped at the grain boundaries, thus inhibiting their diffusion. Hence, with this study, a comprehensive picture highlighting a fundamental property of the material is provided while also setting a theoretical framework in which the interaction between grain boundaries and ionic defect migration can be understood. The study presents the curious case of ionic defect migration in halide perovskites. Using photoluminescence in samples of different grain sizes coupled with molecular dynamic simulation, this study highlights the light‐induced ionic defect movement in relation to the material microstructure. In particular, it is shown that ionic defect migration is blocked by grain boundaries in methylammonium lead iodide perovskite.