Optical Cooling\nof Dot-in-Crystal Halide Perovskites:\nChallenges of Nonlinear Exciton Recombination

Highly efficient anti-Stokes (AS) photoluminescence (PL)\nis observed\nfrom halide perovskite quantum dots (QDs) due to their strong electron–phonon\ninteractions. The AS PL is particularly intriguing, as it suggests\nthe potential for semiconductor optical cooling if the external quantum\nefficiency approaches 100%. However, the PL quantum efficiency in\nQDs is primarily dominated by multiparticle nonradiative Auger recombination\nprocesses under intense photoexcitation, which impose limits on the\noptical cooling gain. Here, we investigate the Auger recombination\nof dot-in-crystal perovskites. We quantitatively estimate the maximum\noptical cooling gain and the corresponding excitation intensity. We\nfurther conducted optical cooling experiments and demonstrate a maximum\nphotocooling of approximately 9 K from room temperature. Additionally,\nwe confirmed that increasing the excitation intensity leads to a transition\nfrom photocooling to photoheating. These observations are consistent\nwith our time-resolved measurements, offering insights into the potential\nand limitations of optical cooling in semiconductor QDs.