Molecular and Morphological Influences on the Open Circuit Voltages of Organic Photovoltaic Devices

Abstract

We explore the dependence of the dark current of C₆₀-based organic photovoltaic (OPV) cells on molecular composition and the degree of intermolecular interaction of several molecular donor materials. The saturation dark current density, J_S, is an important factor in determining the open circuit voltage, V_oc. The V_oc values of OPVs show a strong inverse correlation with J_S. Donor materials that show evidence for aggregation in their thin-film absorption spectra and polycrystallinity in thin film X-ray diffraction result in a high dark current, and thus a low V_oc. In contrast, donor materials with structures that hinder intermolecular π-interaction give amorphous thin films and reduced values of J_S, relative to donors with strong intermolecular π-interactions, leading to a high V_oc. This work provides guidance for the design of materials and device architectures that maximize OPV cell power conversion efficiency.