Tracking and Mitigating Light-Induced Halide Segregation in Perovskites with Film Stress Measurements

Muneeza Ahmad1, Madison Dodd2, Nicholas Rolston1 1Arizona State University, Tempe, AZ, United States /2Brown University, Providence, RI, United States

Mixed halide perovskites are the most suitable top cell candidate for perovskite-silicon tandem solar cells; however, they segregate into iodide and bromide-rich phases under light and have limited long-term reliability. We demonstrate for the first time that thin film stress measurements—both ex situ and in situ— can be used to track degradation and light-induced halide segregation (LIHS), respectively. We show that low-cost, biopolymer additives not only control the residual stresses in the thin film, but also suppress LIHS. The additives show no significant changes in stress and photoluminescence (PL) response when the perovskite films are illuminated under ambient conditions. The controlled real-time in situ monitoring of the relative changes in stress quantifies mechanical durability and LIHS under 1-sun illumination cycles. We therefore demonstrate a mechanism for quantifying phase segregation dynamics and a facile route to a photostable mixed-halide perovskite thin film using a scalable deposition technique with a quench-free processing route using biopolymer additives.