In Situ Proton-Feeding Retards the Deprotonation for Efficient and Stable Red Perovskite Light-Emitting Diodes

Quasi-two-dimensional (quasi-2D) perovskites have shown great potential in the application of light-emitting diodes (LEDs) due to their large exciton binding energy, tunable bandgaps, and solution processability. However, the heavily used spacer cations will cause serious deprotonation reactions in quasi-2D perovskite films, leading to lattice collapse and abundant defect states, which are notorious for fabricating efficient perovskite LEDs (PeLEDs). Herein, we develop an in situ proton-feeding strategy to restrain the deprotonation process in quasi-2D perovskites by introducing a proton-rich Lewis base, namely trifluoromethyl nicotinic acid (TFNA), into the perovskite precursor solutions. The TFNA molecules can donate protons during the growth of quasi-2D perovskite films to simultaneously compensate the deprotonated spacer cations, passivate the defects states by coordinating with Pb²⁺, and improve structural stability by forming hydrogen bonds with organic spacers. This leads to an enhanced photoluminescence quantum yield of 78.8%. The resulting red-emitting quasi-2D PeLEDs achieved a high external quantum efficiency of 27.5% at 660 nm, accompanied by a 3.5-fold enhancement of the operational lifetime (T₅₀) compared to that of the reference device based on pristine perovskite. This work deepens the understanding of the crystallization of quasi-2D perovskite films and provides a new avenue to improve the PeLEDs performance.