A Simple and Robust Method to Quantify Exciton Dissociation Efficiency with High Precision in Non-Fullerene Organic Solar Cells

Abstract

Exciton dissociation at donor-acceptor interfaces remains a critical bottleneck for charge generation in non-fullerene acceptor based organic solar cells (OSCs), yet its precise quantitative assessment is experimentally challenging. Here, we introduce a comparative framework that enables robust determination of the exciton dissociation efficiency ηED by benchmarking a reference morphology against intentionally coarsened morphologies. The latter is achieved by increasing the acceptor content in the blend, thereby enlarging the acceptor domains. This leads to a rise in photoluminescence (non-dissociating fraction of excitons) and decrease in short-circuit current (dissociating fraction). By tracking the relative changes of both these fractions with respect to the photogeneration of excitons, constant prefactors cancel out, eliminating the need for absolute calibrations or numerical assumptions regarding charge-separation and charge-collection efficiencies. The method yields consistent exciton dissociation efficiencies of 96.2 ± 0.4 % for D18:Y6 and 97.2 ± 0.6 % for PM6:DTY6. A pragmatic fully experimental approach is also presented yielding lower bound estimates within 1% uncertainty. Comparison with conventional internal quantum efficiency analysis based on optical simulations confirms the physical validity of the framework while highlighting its markedly superior precision. The proposed methodology provides a broadly applicable tool for identifying dissociation-related losses in state-of-the-art OSCs and supports targeted morphology optimization for continued performance improvements.