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

Abstract

AbstractThe 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.