Superior Stability and Emission Quantum Yield (23% ± 3%) of Single‐Layer 2D Tin Perovskite TEA2SnI4 via Thiocyanate Passivation

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 TEA2SnI4 (TEA = 2‐thiophene‐ethylammonium) is reported. The results reveal that ammonium thiocyanate (NH4SCN) is the most effective additive in enhancing the stability and photoluminescence quantum yield of 2D TEA2SnI4 (23 ± 3%). X‐Ray photoelectron spectroscopic investigations on the thiocyanate passivated TEA2SnI4 nanoplate show less than a 1% increase of Sn4+ 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 TEA2SnI4 is proposed to play a crucial role in preventing the oxidation of Sn2+ and hence boosts both stability and photoluminescence yield of tin perovskite nanoplates. Ammonium thiocyanate (NH4SCN) is introduced during the synthesis of TEA2SnI4 as a surface passivation reagent to mitigate Sn2+ oxidation, yielding the air‐stable tin perovskite nanomaterials with a core–shell like structure. The thiocyanate‐passivated tin perovskite nanoplates display photoluminescence quantum yield as high as 23% ± 3% and remain luminescent for 24 h after exposure to air.