Modeling the effects of molecular length scale electrode heterogeneity in organic solar cells

Kinetic Monte Carlo simulations of planar heterojunction (PHJ) organic solar cells (OPVs) constructed with electronically heterogeneous electrodes are presented which correlate the extent and length scale of electrode heterogeneity with their capacity for collecting photogenerated charge carriers. The PHJ OPV is modeled as an ensemble of discrete 1 nm ³ molecular sites and 1 nm ² electrode sites for which we individually assign various effective activation energies for charge hopping. Utilizing Marcus theory to describe charge transfer reactions within the energetically disordered lattice, described by a Gaussian distribution of discrete site energies, we demonstrate the sensitivity of solar cell device performance to nanometer length scale heterogeneity at the electrode-active layer contact. Such sensitivity is reflected in the steady-state charge density profiles in the vicinity of the electrode-active material interface, charge collection efficiencies, and rates of recombination at the donor-acceptor (D/A) interface. Additionally, we demonstrate how implementation of idealized interlayers placed between the electrode and active layer functions to mitigate the negative effects of electrode heterogeneity.