Synergistic enhancement of the optoelectronic performance and stability of MA and Cs in FAxMAyCs1−x−yPbIzBr3−z single crystals

Abstract

The triple-cation and mixed-halide perovskites FA_xMA_yCs_1−x−yPbI_zBr_3−z have been identified as the optimal perovskite composition for photovoltaic devices due to their exceptional stability and high efficiency. Unfortunately, debates remain regarding the specific contributions of the A-site cations, particularly MA, and further investigation is needed to understand the impact of the composition on the phase stability and optoelectronic properties. The mixed halide is a necessary condition for ensuring the stability of α-FAPbI₃. However, it should be noted that the stability of α-FAPbI₃ is not solely dependent on the mixed halide, as the A-site cations also contribute significantly to enhancing both the stability and photoelectric performance of α-FAPbI₃. In this study, MA and Cs were employed to occupy the shrunken cubo-octahedral voids resulting from the introduction of Br, thereby mitigating lattice strain and enhancing crystal stability. In comparison to FA_0.95Cs_0.05PbI_2.7Br_0.3 (FACs), FA_0.9MA_0.05Cs_0.05PbI_2.7Br_0.3 (FAMACs) demonstrates a lower trap state density, better stability and repeatability, and a higher on–off ratio (∼820) for photodetector devices. This work revealed that the triple-cation and mixed-halide perovskite FAMACs is a better candidate than FACs for replacing Si as a star material for optoelectronic devices.