Carrier Dynamics Relaxation in Highly Monodisperse CsPbBr₃ Perovskite Quantum Dots: The Role of Quantum Confinement

Photophysical investigations of lead-halide perovskite quantum dots (QDs) are crucial for optimizing their integration into optoelectronic devices, leveraging their stability, high photoluminescence quantum yield, and precisely tunable optical properties enabled by quantum confinement. In this work, we systematically study the carrier dynamics of strongly quantum-confined CsPbBr₃ QDs by employing femtosecond transient absorption spectroscopy (fs-TA) across varying excitation intensities. A detailed global quantitative analysis using decay-associated difference spectra (DADS) reveals a significant inverse correlation between quantum dot size and carrier relaxation times. We demonstrate that smaller QDs exhibit slower relaxation kinetics due to intensified carrier-phonon interactions inherent to strong quantum confinement. Furthermore, increasing excitation power notably enhances the hot-phonon bottleneck effect, leading to extended hot-carrier lifetimes. These insights highlight the critical influence of quantum dot dimensions and excitation conditions on carrier dynamics, providing valuable guidance for improved design and control of perovskite-based optoelectronic devices, including LEDs, ultrafast lasers, and hot-carrier photovoltaic cells.