Cs2SnSiF6: A novel lead-free double perovskite for high-efficiency optoelectronics

Abstract

This study employs Density Functional Theory (DFT) calculations to investigate the structural, mechanical, electronic, optical, and dynamic properties of Cs₂SnSiF₆, a novel lead-free double perovskite predicted for the first time through computational modeling. Cs₂SnSiF₆ crystallizes in a cubic structure (Fm-3m) and exhibits a direct bandgap of 1.374 eV (HSE06) at the Gamma point, optimal for single-junction solar cells as dictated by the Shockley-Queisser limit. Spectroscopic limited maximum efficiency (SLME) calculations reveal a theoretical power conversion efficiency of ∼31 % under AM1.5G illumination at 300 K temperature, matching the performance of lead-based analogs like MAPbI₃ and surpassing conventional lead-free perovskites (e.g., Cs₂AgBiX₆, SLME <20 %). The material also displays broad visible-light absorption (α > 10⁵ cm⁻¹) and low reflectivity (<5 % at 200 nm), further underscoring its solar cell potential.

Mechanically, Cs₂SnSiF₆ demonstrates exceptional robustness, with a high bulk modulus (66.64 GPa), low anisotropy (0.327), and ductile Pugh ratio (2.95), ensuring durability under operational stresses. Its thermodynamic stability is confirmed by a negative formation energy (−3.048 eV/atom), high Debye temperature (265 K), and melting point (768 K). Phonon dispersion calculations validate dynamic stability, with no imaginary frequencies detected. These findings position Cs₂SnSiF₆ as a groundbreaking candidate for high-efficiency optoelectronics, including solar cells, LEDs, and photodetectors, while offering a sustainable alternative to toxic lead-based perovskites.