Strain-enhanced performance in ultra-soft CsSn(Br3−xClx) perovskites for flexible optoelectronics

All-inorganic tin-halide perovskites, CsSn(Br 3−x Cl x ), represent promising alternatives to lead-based hybrids, combining reduced toxicity with improved thermal stability. Here, first-principles density functional theory calculations using the Heyd–Scuseria–Ernzerhof are employed to investigate the role of isotropic strain (− 4 to + 4%) on the mechanical, electronic, optical, and environmental stability of this mixed-halide materials. The results show that tensile strain significantly enhances acoustic-phonon-limited carrier mobilities while simultaneously adjusting conduction-band alignment, yielding near-barrier-free electron extraction with typical electron transport layers. Moreover, tensile strain lowers surface energy and weakens water adsorption leading to improved moisture resistance relative to MAPbI 3 . Chloride-rich compositions emerge as optimal, exhibiting ultra-soft mechanical characteristics, superior moisture tolerance, and balanced charge-transport performance. These results demonstrate strain engineering as an effective way to overcoming long-standing stability limitations in tin perovskites, positioning CsSn(Br 3−x Cl x ) as an attractive platform for durable, lead-free flexible photovoltaics and wearable optoelectronics.