Directly imaging the structure–property correlation of perovskites in crystalline microwires

Abstract

Lead halide perovskites have recently emerged as groundbreaking photovoltaic materials due to their low-cost, solution-processed fabrication and extraordinary performance. Despite the rapid improvement in efficiency, perovskite devices often suffer from degradation and poor reproducibility, which are perhaps the greatest barriers for their commercialization. Fundamental understanding of perovskites' structure–property correlation is of great importance to reveal the origins of the instability and advance their practical utility. However, previous research studies mainly focused on perovskite polycrystalline thin films, a morphology with intrinsic grain boundaries that induce interference in such a direct correlation. Here, we develop a method that allows direct visualization of the structure–property correlation in one-dimensional (1D) crystalline perovskite microwires. In contrast to polycrystalline thin films, 1D microwires with well-defined crystal structures are very conducive to explore the fundamentally intrinsic properties of perovskites due to the absence of grain boundaries and a reduced trap state density. In such a clean system, we reveal the stable coexistence of two crystalline components, a MAPbI₃ perovskite phase and a MAPbI₃·DMF intermediate phase, appearing as axially alternating dark and bright domain patterns along individual microwires. We show that the MAPbI₃·DMF phase has inferior optical properties and leads to the degradation and poor reproducibility of perovskites. We further elucidate that laser illumination is an effective method to obtain a homogeneous perovskite structure with high optical quality. Our work provides a new route for fundamental understanding and performance improvement of emerging perovskite materials and devices.