Two‐Dimensional Heterovalent Alloying Hybrid Double Perovskite Solid Solution for Elevating Ferroelastic Photoelectric Response

Abstract Hybrid double perovskites (HDPs), as the main candidates for lead‐free materials, have attracted great attention in the construction of ferroelectrics, ferroelastics, and high‐efficiency photodetectors. However, the photoelectronic performance of HDPs, including bandgap and carrier transport efficiency, is still far behind compared to lead‐based analogues. Excavate effective strategies to bridge this gap has always been an ongoing challenge. Herein, for the first time, we present a family of intrinsic solid solution based on heterovalent metal ions of HDPs, (cyclohexylmethylammonium) 4 (Ag/Bi)X 8 (X = Cl, Br, I). Such solid solution effectively improves the structural stacking mode, and thereby not only inducing 4/ mmmF 2/ m type ferroelastic phase transition but also making a narrower optical bandgap (∼1.74 eV) of (cyclohexylmethylammonium) 4 (Ag/Bi)I 8 lower than that of HDP counterparts. Benefiting from the collaborative overlap of wide absorption range and promoting effect ferroelastic domains on carrier transport, (cyclohexylmethylammonium) 4 (Ag/Bi)I 8 exhibits a photocurrent switching ratio ( I on / I off ) greater than 100 and photoelectric response across the entire UV–vis range. In short, this work provides a new perspective for improving the physical performance of HDPs.