Effect of mechanical forces on thermal stability reinforcement for lead based perovskite materials

Abstract

Stability is one of the major challenges of organic–inorganic hybrid perovskite materials (APbX₃, where A = MA⁺, FA⁺ and Cs⁺, and X = I⁻, Br⁻ and Cl⁻, respectively) in optoelectronic device applications. APbX₃ materials are extremely sensitive to temperature, humidity and oxygen. Although degradation of the materials caused by oxygen and moisture could be partially solved by encapsulation techniques, further improving the stability of perovskites under external heat is still demanding. Generally, APbX₃ would decompose into AX and PbX₂ at the early stage, when it is in a high-temperature environment. In this contribution, we demonstrated that pressure can reinforce the thermal stability of MAPbX₃, by promoting the reverse reaction. The stability reinforcement of MAPbI₃ by mechanical forces was found to be more effective compared with that of MAPbBr₃/MAPbCl₃. Furthermore, we carried out quantitative research to mimic pressure induced reverse reactions, through dry-grinding the powder mixtures of equimolar PbX₂ and AX. We found that the conversion yields and reaction paths were dramatically different depending on the type of organic-cation (A) and halide (X). APbI₃, CsPbBr₃ and CsPbCl₃ can be directly and completely synthesized by the dry grinding method, and thus they are more promising candidates for material recovery by external forces. Meanwhile, it was found that CsPbBr₃ and CsPbCl₃ crystalize via Cs₄PbX₆ (X = Br or Cl) intermediate states. Our results provide a robust strategy for the specific design of perovskite material based optoelectronic devices, especially for applications demanding better stability.