Inhibiting the decomposition of methylammonium using cations with low deprotonation energy

Abstract

A small amount of methylammonium in the CH₃NH₃PbI₃ (MAPbI₃) perovskite precursor solution or on the perovskite surface is decomposed spontaneously, but this is very adverse for the preparation of high-quality MAPbI₃ perovskite and devices in experiments. Herein, proton transfer between the CH₃NH₂ molecule and the cations (H₅O₂⁺, CH₃OH₂⁺, H₂F⁺, and so on), as well as the properties of MAPbI₃ perovskites with H₅O₂ super-alkalis, were studied systematically via high-throughput first-principles calculations and ab initio molecular dynamics simulations. The calculated results indicate that the cations with low deprotonation energy could spontaneously convert the highly volatile CH₃NH₂ molecule into MA⁺ both in the free (solution) form or on the perovskite surface, which strongly suggests that the decomposition of MA⁺ can be inhibited in the perovskite precursor solution or on the MAPbI₃ perovskite surface by using easy-to-deprotonate cations to achieve the self-healing of the MAPbI₃ perovskite. Moreover, the MAPbI₃ perovskites with H₅O₂ super-alkalis showed negative formation energies, stable dynamics performances, tunable direct band gaps, small carrier effective masses, low exciton binding energies, and power conversion efficiencies over 28.70%. These findings suggest that preparing high-quality MAPbI₃ perovskites and their devices may be feasible by using easy deprotonated cations as additives or surface-treatment agents.