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

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)X₈ (X = Cl, Br, I). Such solid solution effectively improves the structural stacking mode, and thereby not only inducing 4/mmmF2/m type ferroelastic phase transition but also making a narrower optical bandgap (∼1.74 eV) of (cyclohexylmethylammonium)₄(Ag/Bi)I₈ 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)I₈ 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.