Nanoscale First-Principles Electronic Structure Simulations of Materials Relevant to Organic Electronics

Abstract

Organic molecular materials have attracted considerable attention as a candidate for next-generation flexible electronics in the near future. However, there still remain open questions on fundamental electronic properties such as mechanisms of the carrier transport and barriers for carrier injection at organic-inorganic heterojunctions. In this review, we illustrate the progresses in first-principles electronic structure calculations of the materials for investigation of the atomic- or molecular-scale electronic properties of organic semiconductor materials, which are in general difficult to observe even with present-day experimental techniques. The theoretical studies not only help elucidate the mechanism of the experimental measurement but also may allow us to gain insights into the essences of the materials properties in terms of the electronic structure. Specifically, in this article, we focus on the first-principles theoretical treatment of the geometric configurations of organic semiconductors and their electronic structure at the level beyond the approximation to the density functional theory (DFT) such as the local density (LDA) and generalized gradient approximations (GGA), i.e., the van der Waals-inclusive methods for describing the weak intermolecular interaction in organic solids and the many-body perturbation theory within the GW approximation for treatment of the charged excitation (quasiparticle) and thus the fundamental gap and the band dispersion of the crystals. Here, we illustrate the recent studies on (i) the effect of the molecular configuration on the quasiparticle energy in organic semiconductors, (ii) the energy level alignment at organic-metal interfaces, and (iii) prediction of the charge injection levels at a surface of organic thin film, i.e., the ionization energy and the electron affinity. Further progresses in theoretical methodologies, being enhanced by rapid progress in computational resource and algorithm, might lead to in silico material simulation or design.