Charge Carriers at Organic–Organic Interfaces

Abstract

Structural order in organic semiconductors is paramount: It reduces energetic disorder, boosts charge and exciton mobilities, and in solar cells assists exciton splitting. Due to spatial localization of electronic states, microscopic descriptions of elementary processes tend to overlook the influence of structural features at a mesoscale. Long-range electrostatic interactions nevertheless probe this ordering, making local properties depend on the mesoscopic order. Using the computational techniques developed in Chap. 3, we show how inclusion of mesoscale order resolves the controversy between experimental and theoretical results for the energy-level profile and alignment in a variety of organic systems, with direct experimental validation. Optimal use of long-range ordering also rationalizes the acceptor-donor-acceptor paradigm for the molecular design of donor dyes in organic solar cells. We calculate the charge-density-dependent open-circuit voltage across planar heterojunctions in excellent agreement with experimental data, based only on crystal structures and interfacial orientation.