Regulated crystallization with minimized degradation for pure-red lead-free perovskite light-emitting diodes

Reducing the lead (Pb) toxicity has remained a huge challenge toward the commercial development of the mainstream Pb-based halide perovskites. Tin (Sn) has been considered as one of the most promising candidates to replace the Pb component, but it still suffers from severe oxidation of Sn²⁺ and poor perovskite morphology. In this work, bifunctional additive engineering by incorporating nicotinohydrazide (NHD) with two effective groups (-N₂H₃ and -C 00000000 00000000 00000000 00000000 11111111 00000000 11111111 00000000 00000000 00000000 O) into the perovskite is employed for improving the device performance of Sn-based PeLEDs. The Sn²⁺ oxidation is greatly suppressed due to the reducibility of -N₂H₃ and strong interaction between -C O and Sn²⁺. Meanwhile, the perovskite film morphology is apparently optimized owing to the distinctly retarded crystallization process. Consequently, a pure-red PeLED emitting at 628 nm is achieved with elevated electroluminescence efficiency and stability, and the CIE coordinates match the BT.2020 standard. These results provide an effective strategy for the development of lead-free PeLEDs.