Strong Self‐Trapped Exciton Emissions in Two‐Dimensional Na‐In Halide Perovskites Triggered by Antimony Doping

Abstract Soft lattice and strong exciton–phonon coupling have been demonstrated in layered double perovskites (LDPs) recently; therefore, LDPs represents a promising class of compounds as excellent self‐trapped exciton (STE) emitters for applications in solid‐state lighting. However, few LDPs with outstanding STE emissions have been discovered, and their optoelectronic properties are still unclear. Based on the three‐dimensional (3D) Cs 2 NaInCl 6 , we synthesized two 2D derivatives (PEA) 4 NaInCl 8 :Sb (PEA=phenethylamine) and (PEA) 2 CsNaInCl 7 :Sb with monolayer and bilayer inorganic sheets by a combination of dimensional reduction and Sb‐doping. Bright broadband emissions were obtained for the first time under ambient temperature and pressure, with photoluminescence quantum efficiency (PLQE) of 48.7 % (monolayer) and 29.3 % (bilayer), superior to current known LDPs. Spectroscopic characterizations and first‐principles calculations of excited state indicate the broadband emissions originate from STEs trapped at the introduced SbCl 6 3− octahedron.