Controllable Transition Metal Cations Doping Enable Efficient and Spectral Stable Pure‐Red Perovskite QLED

Abstract Mixed‐halide perovskite plays important role in wide‐color gamut displays as a vital material for three primary colors. However, halide segregation and caused unstable spectra are the intrinsic problem in mixed‐halide perovskite light‐emitting diodes (PeLEDs) originating from the lattice strain and the resulting defects in perovskite quantum dots (PQDs). Here, smaller transition metal cations are applied to replace Pb 2+ and release lattice strain, which avoids halogen escaping/halide vacancies forming to ensure high photoluminescence quantum yield (PLQY) and stable spectra. However, the actual doping amount is limited by ionic size and chemical environment, which will affect the improvement of optoelectronic performance. Thus, this study proposes a strategy by introducing tri‐n‐octylphosphine to coordinate strongly with metal cations and catch them to participate the nucleation‐growth process. Through doping transition metal cations effectively, the CsPb(BrI) 3 PQDs show high PLQY (92%) and long lifetime (107.83 ns). Further, highly efficient pure‐red PeLEDs with highest external quantum efficiency of 16.86% is fabricated and the spectrum can be stabilized at 630 nm with only 1 nm red‐shift under bias, showing the promising potential of PQDs for next‐generation display.