Electronic and optical excitations at the pyridine/ZnO(10$\overline{1}$0) hybrid interface

TL;DR

This study combines advanced theoretical methods to analyze electronic and optical excitations at a pyridine/ZnO interface, revealing diverse excitonic states and the importance of many-body effects in such hybrid systems.

Contribution

It provides a detailed first-principles investigation of excitations at an inorganic/organic interface, highlighting the non-rigid nature of quasiparticle band shifts and characterizing hybrid excitons.

Findings

Identification of a strongly bound hybrid exciton dominating absorption onset

Diverse electron-hole pair types including hybrid and charge-transfer excitations

Many-body effects cause non-rigid band structure modifications

Abstract

By combining all-electron density-functional theory with many-body perturbation theory, we investigate a prototypical inorganic/organic hybrid system, composed of pyridine molecules that are chemisorbed on the non-polar ZnO($10\overline{1}0$) surface. We employ the $G_0W_0$ approximation to describe its one-particle excitations in terms of the quasi-particle band structure, and solve the Bethe-Salpeter equation for obtaining the absorption spectrum. The different character of the constituents leads to very diverse self-energy corrections of individual Kohn-Sham states, and thus the $G_0W_0$ band structure is distinctively different from its DFT counterpart, i.e., many-body effects cannot be regarded as a rigid shift of the conduction bands. We explore the nature of the optical excitations at the interface over a wide energy range and show that various kinds of electron-hole pairs are formed, comprising hybrid excitons and (hybrid) charge-transfer excitations. The absorption onset is characterized by a strongly bound bright ZnO-dominated hybrid exciton. For selected examples of either exciton type, we analyze the individual contributions from the valence and conduction bands and discuss the binding strength and extension of the electron-hole wavefunctions.