Evolutions of mechanical and optoelectronic properties of Cs₂TeX₆ (X = Cl, Br, I) perovskite under hydrostatic pressure: promising solar cell candidates

Abstract Confronted with environmental contamination and energy scarcity, lead-free vacancy-ordered double perovskite Cs 2 TeX 6 (X = Cl, Br, I) has shown promising potential for optoelectronic applications. In this work, Cs 2 TeCl 6 was synthesized by mechanochemistry with its structure characterized using x-ray diffraction, the aligning of experimental and computational results demonstrate the reliability of the geometrically optimized crystal. First principles calculation was conducted to analyze the evolutions of mechanical, optoelectronic and thermodynamic properties of Cs 2 TeX 6 under hydrostatic pressure from 0 GPa to 40 GPa. Calculated modulus satisfy the stability criteria, indicating structural ductility and stability. Pressure application diminishes lattice parameters and notably narrows their indirect band gaps approach the ideal 1.34 eV for perovskite solar cells at 29.3 GPa, 8.3 GPa, and 0.1 GPa when X goes from Cl to I. The analysis of differential charge density slice under pressure elucidates materials’ photoelectric shifts from the basic electronic alterations, which is a novel research perspective. The density of states results show that the valence band maximum is dominanted by X-p orbitals, while the conduction band minimum by Te-5p and Cs-6s orbitals. Their improved absorption coefficients and dielectric constants under pressure position them as promising materials for applications in perovskite solar cells. Positive phonon spectrum and rapidly decreasing negative Gibbs free energy with temperature confirm the thermal stability of these materials. Finally, the photovoltaic performance of Cs 2 TeI 6 -based cell structures was investigated at varying pressure using SCAPS-1D simulator. The maximum power conversion efficiency was found 22.64 % at 0.1 GPa. This work provides a scientific basis for experimental studies and directions for guiding the modulation of perovskites’ optoelectronic performance through hydrostatic pressure.