Calculation from First-Principles of Golden Rule Rate Constants for Photoinduced Subphthalocyanine/Fullerene Interfacial Charge Transfer and Recombination in Organic Photovoltaic Cells

摘要

The rates of interfacial charge transfer and recombination between the donor and acceptor layers play a key role in determining the performance of organic photovoltaic cells. The time scale and mechanism of these processes are expected to be impacted by the structure of the interface. In this paper we model the kinetics of those processes within the framework of a subphthalocyanine/fullerene donor/acceptor dimer model. Two likely configurations (on-top and hollow) in which the interfacial charge transfer and recombination may occur are studied. The corresponding rate constants are calculated within the fully quantum-mechanical framework of Fermi's golden rule. All the input parameters (excitation energies, electronic coupling coefficients, normal-mode fre-quencies and coordinates, and Huang—Rhys factors) are obtained from density functional theory calculations with density functionals designed to yield accurate results in the case of noncovalently bound systems and charge transfer states. Multiple π~π and charge-transfer excited states are identified and assigned. The kinetics of photoinduced charge transfer is obtained by solving a master equation using Fermi's golden rule rate constants for the electronic transitions between the various excited states. Our results suggest that the hollow configuration may be superior to the on-top configuration and that maximizing its prevalence may improve the performance of subphthalocyanine/fullerene-based photovoltaic cells.