Subphthalocyanine on C$_{70}$ Contact Layer Structure and Properties from First Principles Calculations

Boron subphthalocyanine (SubPc) is a promising donor material for organic photovoltaics, having one of the highest reported open circuit voltages among bilayer OPVs when coupled with C$_{60}$. Recently, C$_{70}$ has attracted attention as a substitute for C$_{60}$, largely due to a broader optical absorption spectrum, which leads to a higher current at relatively high voltages. The structure and electronic properties of SubPc derivatives on C$_{70}$-fullerene were explored using density functional theory (DFT) calculations with added Van der Waals interactions. Total-energy calculations were used to elucidate the initial adsorption derivatives on low index surfaces of C$_{70}$. The dependence of the electronic and optical excitations on the interface morphology is studied within the Green's-function GW and Bethe-Salpeter approaches. Insights gained from these calculations, and how they can be used to improve device efficiency, are discussed.