Multivalent Engineering of Quasi-2D Perovskite Emitter Films for Phase-Pure Blue Perovskite Light-Emitting Diodes

Achieving blue light emission with high quantum efficiency and spectral stability from halide perovskites remains challenging. We herein present a multivalent control strategy using thiourea as an additive to produce phase-pure quasi-2D perovskite films. Thiourea forms coordination interactions (C═S···Pb 2+ ) and hydrogen bonds (PEA-F···H–N) with the perovskite lattice, directing crystallization, suppressing small- n and 3D phases, and passivating defects. This inhibits a heterogeneous lattice structure that promotes efficient energy funneling and facilitated radiative recombination. As a result, the quasi-2D perovskite emitters with thiourea achieve pure-blue emission at 466 nm with a narrow 16 nm bandwidth, corresponding to CIE coordinates of (0.131, 0.055) and ∼99% coverage of the Rec.2100 blue primary. The thiourea-optimized devices also exhibit a high external quantum efficiency of 12.40% and spectral stability under continuous bias. This work highlights the promise of multivalent molecular engineering in advancing high-performance, color-pure blue PeLEDs for next-generation display technologies.