Unveiling the impact of trivalent metal cation transmutation on Cs$_{2}$AgM(III)Cl$_{6}$ double perovskites using many-body perturbation theory

TL;DR

This study uses many-body perturbation theory to analyze how transmuting trivalent metal cations affects the stability and optoelectronic properties of lead-free Cs₂AgM(III)Cl₆ double perovskites, revealing their potential for flexible optoelectronic devices.

Contribution

It introduces a novel cation transmutation strategy to design stable, lead-free double perovskites with tunable optoelectronic properties using advanced first-principles calculations.

Findings

Materials exhibit face-centered cubic structure with high stability.

Bandgaps range from 1.47 to 6.20 eV, suitable for various optoelectronic applications.

Strong optical absorption from near-infrared to ultraviolet regions.

Abstract

Lead-free halide double perovskites A$_{2}$M(I)M(III)X$_{6}$ have garnered significant attention in the past decade as promising alternatives to CsPbX$_{3}$ perovskites, addressing concerns related to lead toxicity and material instability. In this work, we employ a trivalent metal cation transmutation strategy to design a series of inorganic Pb-free halide double perovskites Cs$_{2}$AgM(III)Cl$_{6}$ and perform a comprehensive investigation into their potential for applications in optoelectronic devices. Our first-principles calculations, rooted in density functional theory, demonstrate that these materials possess a face-centered cubic lattice structure while showcasing remarkable thermodynamic, dynamical, and mechanical stability. The G$_{0}$W$_{0}$@PBE electronic bandgap ranges from 1.47-6.20 eV, while the Bethe-Salpeter equation (BSE) indicates strong optical absorption spanning near-infrared to ultraviolet regions for these compounds. Furthermore, the excitonic properties suggest that these perovskites exhibit intermediate exciton binding energies (0.17 to 0.60 eV) and generally longer exciton lifetimes, except for the materials with M(III) = Sc, Y, Tb, and Lu. The Fr\"ohlich model indicates that these materials exhibit intermediate to strong carrier-phonon interactions, with hole-phonon coupling more prominent than electron-phonon coupling. Interestingly, the charge-separated polaronic states are found to be less stable than the bound exciton states, with higher polaron mobility for electrons (4.92-29.03 cm$^{2}$V$^{-1}$s$^{-1}$) than for holes (0.56-8.69 cm$^{2}$V$^{-1}$s$^{-1}$) in these materials. Overall, our study demonstrates that trivalent metal cation transmutation in Cs$_{2}$AgM(III)Cl$_{6}$ enables the creation of stable and lead-free halide double perovskites with exceptional, tunable optoelectronic properties, making them ideal for flexible optoelectronic applications.