Boosting hot carrier cooling in halide perovskite quantum dots via Ni²⁺ doping

Lead halide perovskite quantum dots (PeQDs) generally show slow hot carrier (HC) cooling because of the retarded relaxation of longitudinal optical (LO) phonons induced by hot phonon bottleneck effect. Although the feature is beneficial for designing photovoltaic devices beyond Schottky-Queisser limitation by manipulating HC excess energy, it would be hostile towards light-emitting applications where fast HC cooling is preferred. Herein, we reported a Ni²⁺ doping strategy to effectively boost HC cooling in CsPbI₃ PeQDs and inhibit Auger recombination, giving rise to near-unity photoluminescent quantum yield (PLQY) for the Ni: CsPbI₃ sample. Femtosecond transient (fs-TA) absorption, temperature-dependent PL spectra and theoretical calculations evidenced that Ni²⁺ doping results in the enhancement of electron-LO phonon coupling, the introduction of extra energy states at band edges, the increasement of effective carrier mass, and the modification of phonon dispersion spectra as well as density of states (DOS) of LO phonon modes. These synergistic roles ensure efficient Klemens decay within Ni: CsPbI₃, which facilitates fast decay of hot phonons and break hot phonon bottleneck. Our findings provide a valid route to tackle HC dynamics and pave a way for PeQDs-based efficient light-emitting applications.