Ultrafast Electron‐Transfer Via Hybrid States at Perovskite/Fullerene Interface

Abstract Interfacial charge‐transfer between perovskite and charge‐transport layers plays a key role in determining performance of perovskite solar cells. The conventional viewpoint emphases the necessity of favorable energy‐level alignment of the two components. In recent reports, efficient electron‐transfer is observed from perovskite to fullerene‐based electron‐transport layers even when there are unfavorable energy‐level alignments, but the mechanism is still unclear. Here, using an ultrafast in situ two‐photon photoelectron spectroscopy, real‐time observations of electron‐transfer processes at CsPbI 3 /C 60 interface in both temporal and energetic dimensions are reported. Due to strong electronic coupling, a large amount of interfacial hybrid states is generated at the interfaces, aiding fast photoinduced electron‐transfer in ≈124 fs. This process is further verified by nonadiabatic molecular dynamics simulations and transient absorption experiments. The short timescale explains why electron‐transfer can overcome unfavorable energy‐level alignments, providing a guideline for device design.