Charge Transfer and Spin Dynamics at Hybrid Organic-2D Layered Crystal Interfaces

Two-dimensional (2D) van der Waals heterostructures have received much attention recently because it provides the feasibility in tailoring material properties on the nanoscale. 2D materials such as transition metal dichalcogenide (TMD) can further be combined with other materials such as organic semiconducting crystals to form interfaces with unique properties. In this work, we study the charge transfer properties at zinc phthalocyanine (ZnPc)-MoS₂ and ZnPc-WSe₂ interfaces using time-resolved photoemission spectroscopy. At both interfaces, it is found that the optically excited singlet exciton in ZnPc transfers its electron to the TMD layer in ~ 100 fs. However, back electron transfer can also occur in ~ 1-100 ps at the ZnPc-MoS₂ interface, which results in the formation of a triplet exciton in the ZnPc layer. This back electron transfer process originates from a combination of the strong spin-orbit coupling in TMD crystals and the large exchange interaction in organic crystals. Even though the back electron transfer would reduce the yield of free charge carrier generation at the heterojunction, the spin–selective back electron transfer could provide new possibilities in manipulating electron spin in hybrid electronic devices.