Efficient Pure‐Red Tin‐Based Perovskite Light‐Emitting Diodes Enabled by Multifunctional Lewis‐Base Additives

Abstract Tin‐halide perovskites (THPs) offer a promising alternative to lead‐halide perovskites (LHPs), addressing environmental concerns while providing excellent optoelectronic properties. However, the performance of THP light‐emitting diodes (LEDs) remains inferior to their lead‐halide counterparts due to challenges such as Sn ² ⁺ oxidation, rapid crystallization, and high defect densities. Here, for the first time, a multifunctional Lewis‐base reducing ligand triphenylphosphine (TPP) is reported, which simultaneously suppresses Sn ²⁺ oxidation and passivates defects in 2D THPs TEA ₂ SnI ₄ (TEA represents 2‐thienylethylamine). The P atom in TPP, with its lone pair electrons on the 3p orbital, has low electronegativity and high electron density, which can effectively suppress Sn ²⁺ oxidation. Furthermore, σ‐donation and π‐conjugation effects from the three phenyl groups in the TPP molecule enable it to strongly coordinate with Sn ²⁺ , which passivates defects in TEA ₂ SnI ₄ . These properties enhance the stability and optoelectronic properties of THPs. When the optimized THP films are implemented as active layers in LEDs, they exhibit a narrow electroluminescence full‐width at half‐maximum of 28 nm, Commission Internationale de l'Eclairage x‐coordinate exceeding 0.7, and a peak external quantum efficiency of 10.12%, sevenfold higher than the pristine devices. This work demonstrates the potential of molecular additives to enhance the device performance of tin‐based perovskites.