Pattern‐Matched Polymer Ligpands Toward Near‐Perfect Synergistic Passivation for High‐Performance and Stable Br/Cl Mixed Perovskite Light‐Emitting Diodes

Mixed Br/Cl perovskite nanocrystals (PeNCs) exhibit bright pure‐blue emission benefiting for fulfilling the Rec. 2100 standard. However, phase segregation remains a significant challenge that severely affects the stability and emission spectrum of perovskite light‐emitting diodes (PeLEDs). Here, we demonstrate the optimization of the spacing between polydentate functional groups of polymer ligands to match the surface pattern of CsPbBr1.8Cl1.2 PeNCs, resulting in effective synergistic passivation effect and significant improvements in PeLED performances. The block and alternating copolymers with different inter‐functional group spacing are facilely synthesized as ligands for PeNCs. Surprisingly, block copolymers with a higher functional group density do not match PeNCs, while alternating copolymers enable efficient PeNCs with the high photoluminescence intensity, low non‐radiative recombination rate and high exciton binding energy. Density functional theory calculations clearly confirm the almost perfect match between alternating copolymers and PeNCs. Finally, pure‐blue PeLEDs are achieved with the emission at 467 nm and Commission Internationale de l'Eclairage (CIE) coordinates of (0.131, 0.071), high external quantum efficiency (9.1%) and record spectral and operational stabilities (~ 80 mins) in mixed‐halide PeLEDs. Overall, this study contributes to designing the polymer ligands and promoting the development of high‐performance and stable pure‐color PeLEDs towards display applications.