High Quality CsPbI3−xBrx Thin Films Enabled by Synergetic Regulation of Fluorine Polymers and Amino Acid Molecules for Efficient Pure Red Light Emitting Diodes

Abstract All‐inorganic CsPbX 3 (X = Cl, Br, or I) perovskite thin films are attractive emissive layers for high‐performance light‐emitting diodes (LEDs) due to their precisely tunable bandgaps, excellent color purities, good stabilities, and solution processabilities. However, the fabrication of high‐quality CsPbI 3− x Br x thin films is very challenging because the crystal growth of mixed halide CsPbI 3− x Br x is in low controllability. Herein, a synergetic regulation strategy using fluorine polymer (Poly(vinylidene fluoride‐co‐hexafluoropropylene)) and a small amino acid molecule (L‐Arginine) is developed to fabricate high‐quality CsPbI 3− x Br x thin films for efficient pure red perovskite LEDs. In the fabricated CsPbI 3− x Br x thin film, the fluorine polymer plays a crucial role in confining CsPbI 3− x Br x crystal size at the nanoscale and the small amino acid molecule acts as a passivation agent to reduce the trap‐state density. Under this synergetic effect, a uniform CsPbI 3− x Br x thin film with a high photoluminescence quantum yield up to 40% can be obtained to fabricate an efficient pure red perovskite LED with a maximum external quantum efficiency of 4.5% and a maximum brightness of 3100 cd m −2 . The reported synergistic regulation strategy will open a new avenue to fabricate efficient pure color CsPbX 3 perovskite LEDs.