Publication date: 11th March 2026
Organic solar cells have recently exceeded 20% power-conversion efficiency, prompting a key question: how much further can we push performance? Despite rapid advances, progress is limited by photophysical loss channels that are not yet described within a unified framework. At the heart of the problem lies the intricate excited-state dynamics at the donor–acceptor interface, where excitons, charge-transfer states and fully separated charges are in constant interconversion, governed by the materials’ energetic landscape. A central challenge is to understand and mitigate loss pathways involving singlet and triplet charge-transfer states and local triplet excitons, which ultimately constrain the open-circuit voltage.
In this talk, we share our experimental data and kinetic model that explicitly incorporates the formation and re-splitting of local triplet excitons. Fully parameterised by the interfacial energy offset, this unified framework reproduces key photovoltaic observables – such as the charge-generation efficiency, photoluminescence, electroluminescence and the Langevin reduction factor. In systems with short triplet lifetimes, triplet decay emerges as the dominant recombination pathway, reconciling long-standing experimental findings, including those in benchmark systems like PM6:Y6. In systems with long triplet lifetimes, triplets can be recycled to mitigate this loss channel. The model further offers a mechanistic explanation for the empirically observed link between energy offset, radiative singlet-exciton decay and reduced-Langevin recombination as well as a correlation, and accurately predicts the device efficiency across different material systems.
By connecting excited-state kinetics with macroscopic device metrics, our work provides a unified mechanistic picture of the photophysics in organic semiconductors.
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