Superior Stability and Emission Quantum Yield (23% ± 3%) of Single‐Layer 2D Tin Perovskite TEA 2 SnI 4 via Thiocyanate Passivation

Abstract Tin‐based perovskite, which exhibits narrower bandgap and comparable photophysical properties to its lead analogs, is one of the most forward‐looking lead‐free semiconductor materials. However, the poor oxidative stability of tin perovskite hinders the development toward practical application. In this work, the effect of pseudohalide anions on the stability and emission properties of single‐layer 2D tin perovskite nanoplates with chemical formula TEA 2 SnI 4 (TEA = 2‐thiophene‐ethylammonium) is reported. The results reveal that ammonium thiocyanate (NH 4 SCN) is the most effective additive in enhancing the stability and photoluminescence quantum yield of 2D TEA 2 SnI 4 (23 ± 3%). X‐Ray photoelectron spectroscopic investigations on the thiocyanate passivated TEA 2 SnI 4 nanoplate show less than a 1% increase of Sn 4+ signal upon 30 min exposure to air under ambient conditions (298 K, humidity ≈70%). Furthermore, no noticeable decrease in emission intensity of the nanoplate is observed after 20 h in air. The SCN ‐ passivation during the growth stage of TEA 2 SnI 4 is proposed to play a crucial role in preventing the oxidation of Sn 2+ and hence boosts both stability and photoluminescence yield of tin perovskite nanoplates.