Exciton Dissociation Efficiency in Organic Solar Cells Quantified Via Thermally Induced Acceptor Aggregation and Photoluminescence Analysis

The performance of organic photovoltaics (OPVs) depends critically on the efficiency of exciton dissociation at donor-acceptor interfaces, which is strongly influenced by the morphology. This work presents a method for quantifying the exciton dissociation efficiency leveraging the effect of thermally induced acceptor aggregation. The latter leads to an increase in the volume of pure domains, thereby hindering dissociation and increasing the recombination of excitons. As a result, the photocurrent decreases, while the photoluminescence (PL) of the non-dissociated excitons increases. By correlating changes in absorptance, generated current and PL intensity over aging time, the method delivers robust estimates of the exciton dissociation efficiency, yielding 92.8% for the photoactive material PV-X plus and 95.9% for PM6:DTY6 in their unaged state. The method also captures the decline in dissociation efficiency with aging, demonstrating that acceptor aggregation can become a significant performance-limiting factor. Optical simulations of the device stacks reproduce the initial exciton dissociation efficiencies within their respective uncertainties, suggesting that exciton dissociation limits the internal quantum efficiency. However, the associated error margins are considerably larger, which underscores the enhanced accuracy of the proposed method and its suitability for diagnosing morphology-related losses in OPV performance.