Ultrafast Electron-Transfer Via Hybrid States at Perovskite/Fullerene Interface.

Guan, Zhiqiang; Li, Yang; Man, Ping; Tan, Hongji; Wei, Qi; Liu, Jinjie; Li, Mingjie; Ly, Thuc Hue et al. · Adv Mater · 2024

basic_science · Level V

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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<sub>3</sub>/C<sub>60</sub> 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.