Energy-Level Alignment at Organic/Inorganic Interfaces from First Principles: Example of Poly(para-phenylene)/Rock-Salt ZnO(100)

By means of full-potential all-electron density-functional theory and many-body perturbation theory, we compute the band alignment at a prototypical hybrid inorganic/organic interface. The electronic properties of a model system built of poly(para-phenylene) and rs-ZnO are studied in two different geometries, employing several approaches of increasing sophistication. To this extent, we explore models for predicting the level alignment, which are based on the knowledge of the electronic structure of the individual constituents and are commonly used for semiconductor interfaces. For their evaluation in the context of hybrid materials, we perform an ab initio study of the entire system, including a quasiparticle description of the electronic structure within the G0W0 approximation. Based on this, we quantify the impact of structure, charge redistribution, orbital hybridization, and molecular polarization on the band offsets and the alignment type. We highlight not only known limitations of predicting the level alignment at a hybrid inorganic/organic interface by simple models but also demonstrate how structural details of the interface components impact the results.