Abstract:

In recent years, hybrid lead halide perovskites have attracted significant research interest in the optoelectronic fields owing to their exceptional physical and chemical properties. However, their commercialization process is limited largely because of the sensitive nature of perovskite materials towards external stresses, such as heat, UV irradiance, oxygen, and moisture. Among various perovskite-stabilization methods, deposition of a protective layer over the vulnerable perovskite film via simple atomic layer deposition (ALD) technology is of great potential. However, the corrosive effect of H₂O or O₃ on perovskites, which is used as the oxygen source during ALD process, is one of the main obstacles in the application of regular ALD technology for coating compact and highly conformal layer directly onto the perovskite film. In this study, by introducing bifunctional 5-aminovaleric acid (AVA) crosslinking into the layers of CH₃NH₃PbBr₃ (MAPbBr₃) units, we propose a simple yet effective strategy to prevent the degradation of sensitive perovskite structure during the ALD process when H₂O is used as the oxygen source. The formed crosslinked 2D/3D structure of AVA(MAPbBr₃)₂ perovskite film was extremely dense and ultra-smooth compared to the coarse MAPbBr₃ film. With the passivation and protection of AVA, the AVA(MAPbBr₃)₂ perovskite film exhibited high moisture resistance, thereby leading to the successful deposition of dense and conformal Al₂O₃ protective layer onto the perovskite surface. The deposition of Al₂O₃ layer with different thicknesses had a negligible effect on the crystalline phase and morphology of AVA(MAPbBr₃)₂ film, as confirmed by X-ray diffraction, UV-Vis absorption spectroscopy, and scanning electron microscopy characterizations. The steady-state photoluminescence (PL) intensity and time-resolved PL lifetime of AVA(MAPbBr₃)₂ film was kept almost unchanged before and after the coating of Al₂O₃ layer, suggesting that the thin Al₂O₃ layer did not significantly alter the optical properties of the perovskite material, thereby enabling the potential usages in optical and optoelectronic devices. The thermal stability and water resistance ability of Al₂O₃-coated AVA(MAPbBr₃)₂ film was proven to have greatly improved in accelerated circumstances. No impurities or decomposition were detected for Al₂O₃-coated AVA(MAPbBr₃)₂ film after the long-time annealing at high temperature (150 ℃ for 2 h), whereas the crosslinked 2D/3D structure of bare MAPbBr₃ film quickly broke down at the elevated temperature. Intriguingly, the AVA(MAPbBr₃)₂ film with 15-nm-thick Al₂O₃ coating layer could endure strong water corrosion for at least 10 min when immersed in water. Overall, the proposed strategy could not only give a good reference for successfully depositing metal oxides onto the perovskite films with preservation of the materials' intrinsic properties, but also provide a method of introducing amino acid to passivate and protect the perovskite materials from H₂O corrosion during the ALD process. Therefore, the proposed work has practical potential in improving the device stability against various external stresses under different operating conditions, thereby paving way for various applicational advances.

Key words: Lead halide perovskite, Atomic layer deposition, Crosslinked 2D/3D structure, Thermal stability, Water resistance