Unraveling the Interplay\nof Charge Transfer and Excited\nState Dynamics in MAPbBr<sub>3</sub>/Bi<sub>2</sub>Se<sub>3</sub> Heterostructures

The distinctive surface states of Bi<sub>2</sub>Se<sub>3</sub>,\nrecognized as topological insulators, have garnered considerable\nattention for their phenomenal electronic and optical characteristics.\nHeterostructures (HS) integrating Bi<sub>2</sub>Se<sub>3</sub> have\nemerged as viable prospects for a variety of applications despite\nhurdles such as attaining high-quality interfaces, complicated fabrication\nprocesses, and maximizing optoelectronic performance. The synergistic\ncoupling of Bi<sub>2</sub>Se<sub>3</sub> and halide perovskite materials\nprovides potential such as variable bandgaps and improved charge carrier\nmobility. In this work, we fabricated the HS of Bi<sub>2</sub>Se<sub>3</sub> with MAPbBr<sub>3</sub>, with the aim of understanding changes\nin fundamental properties and excited state dynamics under different\nheterostructuring conditions. We observed the critical role of surface\nmatching conditions in determining lattice compatibility between materials\nand influencing the crystallization of MAPbBr<sub>3</sub> precursor\nsolutions. We demonstrate the occurrence of several phenomena in these\nheterostructures using transient absorption analysis. These include\ncharge transfer, extended carrier recombination lifetimes, and bandgap\nrenormalization. We also observe polaron formation, hot carrier cooling,\nand exciton–exciton annihilation. Additionally, inverse bremsstrahlung\nand excitonic interactions are identified. Moreover, the investigation\nof carrier temperature dependence indicates the participation of phonon\nbottleneck effects and Frohlich phonon emission. Because of their\nability to achieve considerable charge transfer efficiencies resulting\nfrom strong electron–phonon coupling and excitonic interactions,\nwe hypothesize that such heterostructures offer promise for effective\nphotovoltaic and optoelectronic applications. Further exploration\nof the integration of other perovskite materials with Bi<sub>2</sub>Se<sub>3</sub> is crucial for unlocking their full potential in practical\ndevices.