Theoretical Insights into Interfacial Electron Transfer between Zinc Phthalocyanine and Molybdenum Disulfide.

A comprehensive understanding of interfacial charge transfer dynamics is critical for improving the optoelectronic efficiency of organic-transition metal dichalcogenide heterostructures. In this work we have employed density functional theory (DFT) and developed nonadiabatic dynamics simulation approaches to study the photoinduced electron transfer dynamics at the interface of zinc phthalocyanine (ZnPc) and molybdenum disulfide (MoS). Our present results show that ZnPc is adsorbed in a parallel orientation on MoS through a weak van der Waals interaction. Photoirradiation excites an electron of ZnPc into its lowest unoccupied molecular orbital (LUMO), which is primarily located on ZnPc but has a tail on MoS. This enhances the vibronic coupling between the LUMO of ZnPc and adiabatic states of MoS, thereby benefiting the interfacial electron transfer. The LUMO of ZnPc is also calculated to be 0.27 eV higher than the conduction band minimum (CBM) of MoS so that the electron transfer from ZnPc to MoS is thermodynamically favorable. Further nonadiabatic dynamics simulations verify such ultrafast electron transfer and estimate its time scale of ca. 10 fs. In this process, the low-frequency out-of-plane vibration of MoS, and low- and high-frequency in-plane and out-of-plane vibrations of ZnPc are found to play an important role in regulating this interfacial electron transfer. In-depth analysis also reveals that atomic motion induced changes of adiabatic states is a dominant factor leading to such ultrafast interfacial electron transfer. These insights could be useful for understanding charge transfer processes at interfaces of heterostructures.