Interlayer Charge Transfer Coupled with Acoustic Phonon in Organic/Inorganic van der Waals Stacked Heterostructures: Self-Assembled Pt(II) Complex on a PtSe₂ Monolayer

Interlayer charge-transfer (CT) excitons in heterostructures are of great importance because of their crucial roles in manipulating the device performance and many-body quantum behaviors. Nonetheless, enigmas arise in organic/inorganic heterointerfaces because localized excitons and inhomogeneity in organic materials hinder the interlayer CT processes. Here, we demonstrate that the interlayer CT excitons form in the new organic/inorganic heterostructure composed by the Pt­(II) complex 4Me and monolayered transition-metal dichalcogenide PtSe₂. The “edge-on” alignment of 4Me is resolved by high-resolution transmission electron microscopy and grazing-incidence X-ray diffraction. Photoelectron spectroscopies verify that the interlayer CT was promoted by the type-II energy band alignment. Moreover, steady-state vis/NIR spectroscopy captures the interlayer CT optical transition and transient absorption spectroscopies unveil the fast charge separation (0.4 ps) coupled with the out-of-plane acoustic phonon mode (0.40 THz) from the PtSe₂ monolayer, followed by the slow charge recombination (0.86 μs). This work systematically characterizes the morphology of the 2D heterointerface and the photophysical mechanism of interlayer CT processes, which expand the vision of the material design in organic/inorganic heterostructures and monolayer-based devices.