Pseudohalide Anions to Suppress Oxidative Degradation for Efficient Formamidinium-Based Sn–Pb Halide Perovskite Solar Cells
Lian Wang, Zhongxiao Wang, Hui Li, Bohong Chang, Lu Pan, Zhirun Xie, Longwei Yin
Abstract
Although binary Sn–Pb perovskites possess optimal band gap approaching to the Shockley–Queisser limit efficiency, the enhancement on power conversion efficiency (PCE) of Sn–Pb perovskite solar cells (PSCs) is impeded by the detrimental oxidation of Sn2+. Herein, a novel and effective strategy is developed to introduce pseudohalide anion thiocyanate (SCN–) with similar ionic radius to iodide to occupy the X-site of the perovskite lattice, thus restraining the rapid oxidation of Sn2+ to Sn4+. The incorporation of SCN– into perovskite stabilizes the perovskite crystal structure thermodynamically and increases the adsorption-energy-barrier of oxygen molecules. The coordination between Sn2+ and SCN– can reduce the defect density by healing the undercoordinated Sn2+ and suppressing the Sn and I vacancies. With the incorporation of SCN–, the ion migration behavior and lattice strain associated with the defects are remarkably relaxed. The study on carrier dynamics based on steady-state and time-resolved photoluminescence suggests that the carrier lifetime and non-radiative recombination rate of SCN– PSCs can be remarkably prolonged and depressed, respectively. As a result, FASn0.5Pb0.5I3-based PSCs achieve a 14.5% increase in PCE, reaching 13.74% under AM 1.5G illumination. This strategy takes a noteworthy step toward high efficiency and high stability FA-based Sn–Pb PSCs.