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

Soft lattice and strong exciton-phonon coupling have been demonstrated in layered double perovskites (LDPs) recently, therefore LDP represents a promising class of compounds as excellent self-trapped excitons (STEs) emitters for applications in the field of 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% (mono-) and 29.3% (bi-), 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. Our results provide important insights for designing LDPs with broadband emissions.