Rationalizing Electron–Phonon Interactions and Hot Carriers Cooling in 2D to 3D Metal Halide Perovskites

The cooling mechanism of hot carriers (HC) in metal halide perovskites is a topic of debate which gathered huge attention due to its critical role in the performance of perovskite-based optoelectronics. HC cooling in 2D perovskites is faster than in its 3D counterpart, whereas in 2D/3D perovskites cooling becomes faster with decreasing the thickness of the inorganic quantum wells. Using state-of-the art first principles calculations it is showed that the modulation of electron–phonon (e-ph) coupling strength between bending and stretching phonon branches can explain this observation. Starting from the prototype BA2PbI4 and PEA2PbI4 2D perovskites, e-ph coupling of individual phonon modes is investigated for 2D/3D perovskites with n = 1 and 3, along with a vis-à-vis comparison with the prototypical 3D MAPbI3 system. This study shows that e-ph coupling with high-frequency stretching phonon modes in the 60–120 cm−1 range is highest for n = 1 while it decreases with increasing the quantum well layers, by approaching the 3D bulk limit where e-ph coupling with low-frequency bending phonon modes (<60 cm−1) is dominant. Longer spacer cations with identical quantum well structures have a limited impact on the e-ph coupling, highlighting that the primary factor governing HC cooling is the quantum confinement within the inorganic sublattice. This study provides an advancement in the understanding of the mode-specific e-ph mediated HC cooling mechanism in metal-halide perovskites and can provide a route map toward tuning the e-ph interaction, which is instrumental for effectively gathering HC in solar cell devices.