Unravelling a Zigzag Pathway for Hot-Carrier Collection at CH3NH3PbI3/Graphene Interfaces

The capture of photoexcited deep-band hot carriers, excited by photons with energies far above the bandgap, is of significant importance for photovoltaic and photoelectronic applications since it is directly related to the quantum efficiency of photon-to-electron conversion. By employing time-resolved photoluminescence and state-of-the-art time-domain density functional theory, we reveal that photoexcited hot carriers in organic-inorganic hybrid perovskites prefer a zigzag interfacial charge-transfer pathway, i.e., the hot carriers transfer back and forth between CH3NH3PbI3 and graphene, before they reach a charge separated state. Driven by quantum coherence and interlayer vibrational modes, this pathway at the semiconductor-graphene interface takes about 400 femtoseconds, much faster than the relaxation process within CH3NH3PbI3 (in several picoseconds). We further demonstrate that the transfer rate of the pathway can be further enhanced by interfacial defects. Our work provides a new insight for the fundamental understanding and precise manipulation of hot-carrier dynamics at the complex semiconductor-graphene interfaces, paving the way for highly efficient photovoltaic and photoelectric device optimization.