Kinetic Monte Carlo Study of the Role of the Energetic Disorder on the Open-Circuit Voltage in Polymer/Fullerene Solar Cells

Abstract

One of the major factors limiting the efficiency in organic solar cells (OSCs) is the low open-circuit voltage (Voc). Existing theoretical studies link the Voc with the charge transfer (CT) state and non-radiative recombination. However, also morphology and energetic disorder can have a strong impact on the Voc within realistic 3D bulk-heterojunction OSCs. In this work, we present a kinetic Monte Carlo study on the role of the energetic disorder on the maximum open-circuit voltage. In particular, we compute the quasi-Fermi level splitting for different energetic disorder and analyze the impact of the energetic disorder at the donor-acceptor interface as well as correlations in the site energies on the open-circuit voltage. Our results show that the interface energetic disorder is strongly controlling the maximum Voc. In the presence of a higher interface disorder, both the total charge density and non-geminate recombination increase, and a reduced Voc is observed. Furthermore, the correlated morphologies show an increase in the maximum Voc and a reduced impact of the energetic disorder.