Tuning Hot-Carrier Temperature in CsPbBr₃ Perovskite Nanoplatelets through Metal Halide Passivation

High carrier temperature and slow carrier cooling make perovskite nanostructures potential candidates for hot-carrier solar cells. Here, using time-resolved photoluminescence spectroscopy, hot-carrier dynamics is reported in strongly confined three-monolayer quasi-2D CsPbBr₃ perovskite nanoplatelets characterized by sharp excitonic peaks in the absorption spectrum and narrow emission peaks in the blue region. Treatment with a PbBr₂-ligand solution resulted in a remarkable seven-fold increase in photoluminescence intensity, attributed to effective passivation of surface defects due to lead(II) and bromide vacancies. Further investigations using time-resolved emission spectroscopy revealed consistent carrier cooling times of ∼300 fs for both pristine and treated nanoplatelets, indicating similar fundamental hot-carrier cooling processes. Notably, treated nanoplatelets exhibited higher carrier temperature (∼700 K), linked to increased radiative carrier density after defect passivation. This work demonstrates that treatment of quasi-2D CsPbBr₃ perovskite nanoplatelets with metal halides substantially improves the optoelectronic properties. Notably, hot-carrier temperatures can be increased significantly while preserving the cooling time.