Halogen stoichiometry tailoring of all inorganic double halide perovskite for photoelectrochemical hydrogen production applications

Abstract

The search for stable, non-toxic, and efficient alternatives for solar energy conversion remains a key challenge in advancing optoelectronic and photocatalytic technologies. In particular, the ability to precisely tune the optical band gap is essential for optimizing light absorption and charge carrier dynamics in photocatalytic processes such as the hydrogen evolution reaction (HER). Lead-free double halide perovskites offer a promising solution due to its structural flexibility, chemical stability, and compositional tunability. In this study, Cesium (Cs) based lead free double halide perovskites, cubic phase (Fm3̅m) Cs<inf>2</inf>Sn(Br<inf>x</inf>Cl<inf>1-x</inf>)<inf>6</inf> (0 ≤ x ≤ 1) were synthesized via solution supersaturation recrystallization method enabling precise halide composition tuning. UV–Vis spectroscopy reveals the controlled band gap variation from 5.59 eV to 4.74 eV upon the halogen regulation (increasing Br content). All samples showed excellent thermodynamic stability till 350 °C. Significantly, the bromide-richer Cs<inf>2</inf>SnBr<inf>5.3</inf>Cl<inf>0.7</inf> exhibited a higher negative heat flow than the chloride-rich double halide perovskite, whereas Cl content shows a lower and stable heat flow profile. The mixed halide, Cs<inf>2</inf>SnBr<inf>3.6</inf>Cl<inf>2.4</inf>, proved to be most effective catalyst amongst the series for water splitting under illumination due to its superior responsiveness to light, steady increase in photocurrent density till 1.6 mA/cm2, favourable early onset potential of ̴ 0.15 V under AM 1.5 G illumination, and flat profile in dark. Also, it exhibited small internal resistance to charge carriers which indicates towards less charge-carrier recombination. Overall, the material demonstrates notable photostability over prolonged operation. These results highlight the potential of halide alloying in Sn-based double halide perovskites as a viable strategy to realize efficient and stable photoanodes for solar hydrogen production. © 2025 Elsevier B.V., All rights reserved.