Suppression of ion migration and improvement of electronic properties for CsPbI₂Br via organic amine substitution

CsPbI₂Br perovskite has attracted significant attention in the field of photovoltaics (PVs) due to its superior optoelectronic properties and low cost. However, ion migration caused by defects is one of the reasons that affects the efficiency and stability of PVs. Organic cations substitution is a popular experimental method for effectively suppressing ion migration. It is necessary to choose suitable organic cation, study the internal mechanism and explore the effect of organic cations on suppression of ion migration. By studying surface properties of CsPbI₂Br, it is found that the small ionic radius, weak interaction between ions and little ion charge are the main internal factors promoting the migration of halogen ions. In addition, the electric field is a very important external factor that induces ion migration. And ion migration barrier decreases by 0.1 eV under the effect of 0.3 V electric field. Organic amine ions (BA⁺, PEA⁺, 1 T⁺, and 2P⁺) are introduced to substitute Cs⁺ at the surface of mixed-halide perovskite. And the results show organic amine ions with large conjugated lengths can regulate the interaction between Pb and halogens, reducing defect formation and charge loss in surface structure, regulating band edge states and suppressing halide ions migration effectively. This work delves into the migration of mixed halogen ions and proposes effective organic substitution strategies to suppress ion migration of mixed-halide perovskite.