Enhancing Performance and Stability of Tin Halide Perovskite Light Emitting Diodes via Coordination Engineering of Lewis Acid–Base Adducts

For resolving toxicity issues of Pb‐based perovskites, Sn‐based perovskites have been widely studied as a promising alternative due to similar valence electron configuration between Sn2+ and Pb2+. However, desired Sn2+ in the precursor solution and film is easily oxidized to Sn4+, causing detrimental Sn vacancies and impurities in the films. Unfortunately, dimethyl sulfoxide, a ubiquitously used Lewis base for the fabrication of high‐quality perovskite thin films via the adduct approach, further accelerates the oxidation of Sn2+ in the precursor solution. Herein, N,N′‐dimethylpropyleneurea (DMPU) is proposed as an alternative Lewis base for the fabrication of high‐quality Sn‐based perovskite thin films. The strongly coordinating Lewis base DMPU is shown to suppress the oxidation of Sn2+ in the precursor solution while promoting growth of uniform and highly crystalline thin films. The PEA2SnI4 perovskite light emitting diode (PeLED) based on DMPU demonstrates dramatically improves luminance (L): a more than sixfold enhanced external quantum efficiency (EQE) and better operational stability than those of the device fabricated without DMPU. The optimum PeLED based on DMPU achieves a maximum L and EQE of 68.84 cd m−2 and 0.361%, respectively. This study provides an important methodological base for studying Sn perovskites for development of high‐performance and eco‐friendly PeLEDs. By adopting Lewis bases with varying coordinating ability, interplays between the coordinating ability of the Lewis base and tin halide perovskite film quality is unraveled. The strongly coordinating N,N′‐dimethylpropyleneurea suppresses oxidation of Sn2+ in the precursor solution while promoting growth of uniform and highly crystalline Sn perovskite thin films for achieving high‐performance lead‐free perovskite light emitting diodes.