Lead‐Free Double Perovskite Cs₂AgInCl₆

Abstract

Lead‐free halide perovskites have drawn wide attention as alternatives to their toxic and poorly stable lead‐based counterparts. Among them, double perovskites with Cs2AgInCl6 composition, often doped with various elements, have been in the spotlight owing to their intriguing optical properties, namely, self‐trapped exciton (STEs) emission and dopant‐induced photoluminescence. This interest has sparked different synthesis approaches towards both crystals and nanocrystals, and the exploration of many alloy compositions with mono‐ and trivalent cations other than Ag+ and In3+. In this Minireview we describe the recent developments on Cs2AgInCl6 bulk crystals and nanocrystals, their synthesis strategies, intrinsic optical properties, and tunable photoluminescence originating from different alloying and doping effects. We also discuss progress on computational studies aimed at understanding the thermodynamic stability, the role of defects, and the origin of photoluminescence in relation to the STEs and the direct band gap character.

Boosting the Self‐Trapped Exciton Emission in Alloyed Cs2(Ag/Na)InCl6 Double Perovskite via Cu+ Doping

“…The phonon energy ( ћω phonon ) and Huang‐Rhys factor ( S ) were calculated to be 29.6 meV and 41.1 for Cs 2 (Ag/Na)InCl 6 and 28.8 meV and 43.4 for Cs 2 (Ag/Na)InCl 6 : 1.0%Cu + , respectively (Figure 2e,f ), which are generally consistent with those reported in Cs 2 AgInCl 6 and Cs 2 (Ag/Na)InCl 6 . [ 3 , 7 ] The fitted phonon energies were also close to that (36.5 meV) of the A 1g longitudinal optical phonon mode of [InCl 6 ] 3− octahedron determined by Raman spectra (Figure S10 , Supporting Information), suggesting a dominant phonon mode of A 1g involved in the electron−phonon coupling. [ 19 ] Such large S values indicate strong electron−phonon coupling, which favors the formation of STEs in the soft lattice of Cs 2 (Ag/Na)InCl 6 : 1.0%Cu + and accounts for the broadband (≈590 meV) and large Stokes shift (240 nm) of the STE emission (Figure S11 , Supporting Information).…”

“…To circumvent the limitation of DPs, it is essential to modify their bandgap and transition attributes by engineering the B site of the materials through metal ion doping or alloying. [ 7 ] In this regard, d‐, f‐, and s‐electron ions such as Mn 2+ , Cr 3+ , Tb 3+ , Yb 3+ , Er 3+ , Bi 3+ , In 3+ , and Sb 3+ have been established as effective dopants in DPs to modulate their electronic structures and boost their PL efficiencies. [ 8 ] Specifically, broadband white‐light emission with a quantum yield (QY) of 86% was realized in the alloyed Cs 2 (Ag 0.60 /Na 0.40 )InCl 6 : Bi 3+ crystals by breaking the parity‐forbidden transition through lowering the symmetry of the STE wavefunction.…”

Near‐Infrared Afterglow and Related Photochromism from Solution‐Grown Perovskite Crystal

“…Unfortunately, the optical transition (Γ 4 + →Γ 1 + ) in pristine Cs 2 AgInCl 6 crystal was parity forbidden, resulting in a low PL QY upon excitation. [ 20 ] To activate the photoluminescence (PL), both Yb and Na ion were intentionally doped with a nominal concentration of 40 mol% and 20 mol%, respectively. Based on the equivalent charge of ions, Na + and Yb 3+ were expected to substitute the lattice site of Ag + and In 3+ , respectively ( Figure a).…”

Lead‐Free Halide Double Perovskite Nanocrystals for Light‐Emitting Applications: Strategies for Boosting Efficiency and Stability

“…The existing several reviews only provide a brief introduction on synthesis, stability, band gap engineering, doping, and application of currently studied HDP nanocrystals. [ 85–88 ] However, the strategies for improving optical properties and stability of colloidal HDP nanocrystals have not been summarized systematically.…”