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 is 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.