Improved Crystallinity and Defect Passivation for Formamidinium Tin Iodide-Based Perovskite Light-Emitting Diodes

The toxicity of lead (Pb) presents a critical challenge for the application of perovskite optoelectronics. In tin (Sn) perovskite, Sn²⁺ is easily oxidized to Sn⁴⁺ during the crystallization process. The uncontrollable oxidation process affects the crystallinity of perovskite films and leads to nonradiative traps within the films, resulting in poor device performance. Herein, we improve the efficiency of formamidinium tin iodide (FASnI₃)-based perovskite LEDs (PeLEDs) through the inclusion of phenyl-thioure (PTC), which enhances crystallinity and suppresses oxidation of the Sn perovskite emitters. We achieve a high-performance near-infrared FASnI₃-based PeLED with a peak external quantum efficiency (EQE) of 6.4% and a maximum radiance of 117 W sr^-1 m^-2. The devices exhibit operational lifetimes (T₅₀) of ∼12.4 h under a constant current density of 10 mA cm^-2, representing some of the most stable FASnI₃-based PeLEDs. Our work explores a pathway for regulating crystallinity, inhibiting oxidation, and passivating defects in lead-free Sn-based PeLEDs.