Space-time dynamics of charge carriers in an energetically and spatially disordered bulk heterojunction (BHJ) organic photovoltaic (OPV) system based on kinetic Monte Carlo (KMC) simulations

Abstract

Abstract Charge transport and recombination in organic photovoltaic (OPV) devices are strongly governed by the nanoscale morphology and the energetic disorder, yet their coupled impact remains insufficiently quantified. Here, we employ a kinetic Monte Carlo framework with explicitly resolved donor–acceptor morphologies generated via an Ising–Kawasaki phase-separation model to investigate the morphology dependent charge dynamics in bulk heterojunction OPVs. The systematic variation of domain size, interfacial mixing, and energetic disorder reveals clear quantitative trends in carrier mobility, lifetime, and recombination kinetics. The simulations show that excessively fine morphologies (<10 nm domains) enhance recombination through increased interfacial encounter rates, while overly coarse morphologies reduce the carrier extraction due to the disrupted percolation pathways. The optimal charge transport emerges for the intermediate domain sizes (≈15–25 nm) with continuous percolation networks. The energetic disorder is found to modulate the recombination indirectly by increasing the carrier localization and the spatial separation, leading to delayed recombination dynamics rather than uniform suppression. The transient carrier decay exhibits a non-monotonic behaviour arising from the morphology induced trapping and detrapping within the percolating networks. These results establish a direct physical connection between the morphology descriptors, the energetic disorder, and the macroscopic device-relevant observables. The findings provide design guidelines for morphology optimization in OPVs and highlight the relevance of controlled disorder in emerging non-fullerene and tandem OPV architectures.