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) Cs2NaInCl6, we synthesized two 2D derivatives (PEA)4NaInCl8:Sb (PEA=phenethylamine) and (PEA)2CsNaInCl7: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 [SbCl6]3− octahedron.

Excitation‐Dependent Emission in All‐Inorganic Lead‐Free Cs2ScCl5·H2O Perovskite Crystals

“…[ 12–17 ] The strong exciton–phonon coupling and soft lattice of low‐dimensional metal halides can facilitate the formation of self‐trapped exciton (STEs) which have characteristic broadband emission with large Stokes shift. [ 18,19 ] Therefore, multiple photoluminescence (PL) centers may coexist in a low‐dimensional metal halide, such as radiative cations, [ 2 ] free excitons, [ 20 ] STEs, [ 21 ] defects, [ 22 ] and doping ions. [ 23 ] The coexisting PL centers may lead to excitation‐wavelength dependent emission.…”

Transformation between the Dark and Bright Self-Trapped Excitons in Lead-Free Double-Perovskite Cs2NaBiCl6 under Pressure

“…The lead halide perovskite materials with a chemical formula of APbX 3 (A = Cs + , CH 3 NH 3 + , or HC­(NH 2 ) 2 + , X = Cl – , Br – , I – ) have attracted widespread interest due to their outstanding optoelectronic properties, such as a long carrier diffusion length, a high photoluminescence (PL) quantum yield (QY), a tunable band gap, and high carrier mobility. − However, the toxicity of Pb is a threat to the human body and the environment. , As an alternative, the lead-free double perovskites based on Bi 3+ , Sb 3+ , and In 3+ have been developed to conquer the toxicity and increase the stability. , Unfortunately, pure double perovskites, such as Cs 2 NaBiCl 6 , Cs 2 NaInCl 6 , and Cs 2 AgInCl 6 , exhibit poor luminescence properties due to the dark transition of the free excitons and self-trapped excitons (STEs), which could hinder their commercialization and industrialization in the lighting field. Because the properties of STEs profoundly depend on the inorganic structure distortion, the STE emission could be improved by chemical tailoring (doping, alloying, and reducing the dimensionality), which could result in moderate lattice distortion. − Notably, the perovskite is sensitive to external stimuli, such as temperature and pressure, due to the soft lattices of metal halides. Accordingly, the inorganic octahedron in the lead-free double perovskite could also be modified by applying external stimuli, especially pressure.…”

Emission‐Color‐Tunable Pb−Sn Alloyed Single Crystals with High Luminescent Efficiency and Stability

“…[5][6][7][8] strong phonon-exciton interactions in soft crystal lattice of low-dimensional structure make the excitons easily self-trapped in photo-induced transient lattice defects, thus leading to Stokes-shifted, broadened luminescence during the relaxation process. [30][31][32][33][34] Moreover, alternated organic and inorganic sublattices give rise to an intensive quantum confinement effect and large exciton binding energy, resulting in high radiation recombination efficiency and PLQY. [26][27][28][29][30][31][32][33][34] Though some fruitful results have been achieved, by far, their applications have been still limited to UV-pumped white-light-emitting diodes.…”

“…[30][31][32][33][34] Moreover, alternated organic and inorganic sublattices give rise to an intensive quantum confinement effect and large exciton binding energy, resulting in high radiation recombination efficiency and PLQY. [26][27][28][29][30][31][32][33][34] Though some fruitful results have been achieved, by far, their applications have been still limited to UV-pumped white-light-emitting diodes. [35] Thus, it is of great interest and significance to explore the multifunctional metal halide luminescent materials.…”