Multifunctional FA‐Triflate Treatment for Efficiency and Reliability Enhancements of Quasi‐2D Perovskite Light‐Emitting Di odoes

Abstract The quasi‐2D perovskite family, PEA₂(FA 0.7 Cs 0.3 ) n‐1 Pb n Br₃ n+1 ( n = 2, 3, …, ∞), has emerged as an efficient emission layer for next‐generation perovskite light‐emitting diodes (PeLEDs) due to its self‐aligned multi‐quantum well structure of mixed phases, facilitating efficient energy transfer from lower to higher n‐phases compared to bulk perovskites. However, despite their advantageous energy transfer characteristics, quasi‐2D perovskites have suffered from efficiency and stability issues. During the formation of quasi‐2D perovskite films, internal defects arise, and the predominant presence of lower n‐phase domains in the internal phase distribution leads to susceptibility to external environmental conditions, which are crucial for stability. Here, an approach is proposed to simultaneously enhance the emission efficiency and stability of quasi‐2D perovskites by introducing formamidinium trifluoromethanesulfonate (FA‐Triflate). FA‐Triflate effectively suppresses the formation of lower n‐phases, passivates intrinsic defects, and enhances humidity resistance by improving hydrophobicity. This approach increased the photoluminescence quantum yield of quasi‐2D perovskite films from 52.2% to 70.4%. PeLEDs with FA‐Triflate‐treated quasi‐2D perovskites show an improvement in external quantum efficiency from 6.4% to 16.6%, along with a device lifetime extension of over 3 000%. These findings demonstrate that FA‐Triflate treatment significantly enhances the overall emission efficiency and stability of quasi‐2D perovskite films for optoelectronic applications.