Superhalogen modulation: an effective approach for minimizing light-induced halide segregation in MAPb(I0.7Br0.3)3

Abstract

Significant reduction of light-induced halide segregation in organic–inorganic lead mixed-halide perovskites is essential for their implementation in tandem solar cells with existing silicon technology. Here, we address this challenge by a “One-stone-for-two-birds” strategy in which superhalogen anions of the molecular additive facilitate the reduction of halide defects and cations of the molecular additive play a role as a “controller” in the crystallization kinetics. We elucidate the mechanism by which BF₄⁻ substitution reduces light-induced phase segregation with different concentrations of BF₄⁻ at room temperature. From the bleach growth kinetics and segregation rate constant, we identify that 0.8% molar BF₄⁻ substitution in MAPbI_2.1Br_0.9 results in minimum segregation, and thermodynamic arguments successfully explain the phenomena. Other experimental results, such as X-ray diffraction and photoluminescence under illumination, support our observation with assistance from stochastic simulation results for light-induced halide segregation dynamics. Consequently, the improved photovoltaic performance and enhanced photostability corroborate that suppressed halide segregation impacts device performance.