Stable, Near‐Unity‐PLQY CsPbBr ₃ QDs by In Situ Hydroxyl‐Terminated Polystyrene Ligands

Halide perovskite quantum dots (PQDs) possess outstanding optical properties for display technologies, but their commercial use is limited by surface defects and poor environmental stability. In this work, we introduce hydroxyl‐terminated polystyrene (PS–OH) as a bifunctional ligand incorporated directly during CsPbBr ₃ PQD synthesis. The terminal ‐OH groups provide strong coordination to under‐coordinated Pb ²⁺ sites, suppressing nonradiative recombination, while the polystyrene backbone forms a protective hydrophobic shell. This dual action leads to substantially enhanced photoluminescence quantum yield and substantially improved resistance to moisture‐induced degradation. When used as a color‐conversion layer on top of blue LEDs, the PS–OH modified PQDs enable more efficient photon down‐conversion and improved device‐level performance. These results demonstrate that functionalized polymers, employed as in situ ligands, offer a powerful approach for stabilizing and enhancing brightness of perovskite quantum dots for advanced optoelectronic applications.