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This research investigates the structural, optical, and thermal properties of lead-free halide double perovskites Cs2RbYX6 (X = Cl, Br, I) using computational methods.

May 28, 2026

Advanced Computational Study on the Lead‐Free Halide Double Perovskites Cs 2 RbYX 6 (X = Cl, Br, I): Insights into Structural, Optical, and Thermal Properties

Key Points

This research investigates the structural, optical, and thermal properties of lead-free halide double perovskites Cs2RbYX6 (X = Cl, Br, I) using computational methods.
First-principles calculations using density functional theory (DFT)
Structural optimization with generalized gradient approximation
Optical properties analyzed with Tran–Blaha modified Becke–Johnson (TB–mBJ) potential and thermodynamic properties assessed using quasi-harmonic approximation (QHA)
The direct bandgaps range from 6.53 eV (Cs2RbYCl6) to 4.07 eV (Cs2RbYI6) as X changes from Cl to I
The cubic Fm‐3m phase is confirmed as mechanically stable and ductile
These materials demonstrate positive Seebeck coefficients and increasing ZT with temperature, making them promising for thermoelectric applications

Abstract

ABSTRACT The physical properties of halide double perovskites Cs 2 RbYX 6 (X = Cl, Br, I) were investigated using first‐principles calculations within the framework of Density Functional Theory (DFT). The structural optimization was performed using generalized gradient approximation, while the electronic, optical, and thermoelectric properties were analyzed using the Tran–Blaha modified Becke‐Johnson (TB‐mBJ) potential. The elastic constants and related mechanical parameters were computed using the IR‐elast program, confirming the cubic Fm‐3m phase to be mechanically stable and ductile. Thermodynamic properties were evaluated utilizing the quasi‐harmonic approximation (QHA) framework. These compounds have substantial UV light optical absorption with direct bandgaps (6.53 eV for Cs 2 RbYCl 6 to 5.41 eV for Cs 2 RbYBr 6 and 4.07 eV for Cs 2 RbYI 6 ) that decrease from Cl to I. Materials containing Cs 2 RbYX 6 show promise as lead‐free thermoelectric and optoelectronic alternatives due to their positive Seebeck coefficients and rising ZT with temperature.

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