Ligand Engineering Enables Efficient Pure Red Tin‐Based Perovskite Light‐Emitting Diodes

With increasing ecological and environmental concerns, tin (Sn)‐based perovskite light‐emitting diodes (PeLEDs) are competitive candidates for future displays because of their environmental friendliness, excellent photoelectric properties, and low‐cost solution‐processed fabrication. Nonetheless, their electroluminescence (EL) performance still lags behind that of lead (Pb)‐based PeLEDs due to the fast crystallization rate of Sn‐based perovskite films and undesired oxidation from Sn2+ to Sn4+, leading to poor film morphology and coverage, as well as high density defects. Here, we propose a ligand engineering strategy to construct high‐quality phenethylammonium tin iodide (PEA2SnI4) perovskite films by using L‐glutathione reduced (GSH) as surface ligands toward efficient pure red PEA2SnI4‐based PeLEDs. We show that the hydrogen‐bond and coordinate interactions between GSH and PEA2SnI4 effectively reduce the crystallization rate of the perovskites and suppress the oxidation of Sn2+ and formation of defects. The improved pure red perovskite films not only show excellent uniformity, density, and coverage but also exhibit enhanced optical properties and stability. Finally, state‐of‐the‐art pure red PeLEDs achieve a record external quantum efficiency of 9.32 % in the field of PEA2SnI4‐based devices. This work demonstrates that ligand engineering represents a feasible route to enhance the EL performance of Sn‐based PeLEDs. The performance of eco‐friendly PEA2SnI4 perovskite light‐emitting diodes (PeLEDs) lags far behind that of lead‐based PeLEDs. We demonstrated a ligand engineering strategy that uses GSH as a surface ligand to strongly interact with I− and Sn2+ in perovskites, which thus reduces the film crystallization rate and suppresses the oxidation of Sn2+ ions. Pure red PeLEDs based on the modified PEA2SnI4 achieve a record EQEmax of 9.32 %.