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 Pb