The importance of gap states for energy level alignment at hybrid interfaces

Highlights: • The electronic structure of CuPc on related layered van der Waals materials is compared. • Gap states need to be considered to understand energy level alignment. • Hybrid interfaces require new models of the interfacial electronic structure. - Abstract: Energy level alignment and electronic structure at organic semiconductor interfaces must be controlled to ensure efficient carrier harvesting or injection in next-generation organic optoelectronic technologies. In this context, hybrid organic/inorganic semiconductor interfaces exhibit particularly rich physics. Here, we show that states in the band gap of the inorganic layered van der Waals dichalcogenide SnS₂ play an important role in determining energy level alignment at the hybrid interface with copper phthalocyanine (CuPc). By taking advantage of the closely related CuPc film growth on SnS₂ and the well-studied interface of CuPc/HOPG, we are able to trace spectroscopic differences to the fundamentally different electronic interactions across the two interfaces. We provide a detailed picture of the role of gap states at the hybrid interface and shed light on the electronic properties of inorganic semiconductors in general and metal dichalcogenides in particular.