Ma, J.; Amsalem, P.; Schultz, T.; Shin, D.; Xu, X.; Koch, N.: Energy Level Alignment at the C60/Monolayer-WS2 Interface on Insulating and Conductive Substrates. Advanced Electronic Materials 7 (2021), p. 2100425/1-9
10.1002/aelm.202100425
Open Access Version
Abstract:
Combining a transition metal dichalcogenide monolayer (ML) and molecular semiconductors is an attractive route for forming nanoscale hybrid van der Waals heterostructures with potentially novel (opto-)electronic properties. The energy level alignment at the hybrid interface governs these properties, but precise determination of the interfacial electronic structure is challenging due to the pronounced excitonic nature of both components and the non-trivial band structure of the inorganic ML. For instance, dielectric screening by the supporting substrate of such a heterostructure may impact the energy levels, but very few experiments have attended to this important issue to date. Here, it is shown how photoelectron spectroscopy can be used to unravel the energy level line-up at the C60/ML-WS2 interface supported on an insulating (sapphire) and a semi-metallic (graphite) substrates. On both substrates, an almost identical staggered type-II level alignment is determined. However, C60/ML-WS2 exhibits stronger n-type characteristics on sapphire, which is suggested to be due to native donor-type defects of ML-WS2. While these remain occupied and active on the insulating substrate, they are emptied into the charge reservoir of the conductive substrate. These insights should be considered in the future design of functional heterostructures of inorganic ML and molecular semiconductor materials.