When the Triplet State Doesn’t Matter: Insights into Its Impact on <i>V</i>_OC

Organic solar cell efficiency, exceeding 20%, is limited by recombination losses from singlet and triplet charge-transfer (CT) states and local triplet excitons, impacting open-circuit voltage (<i>V</i> _<i>OC</i> ). Using PM6:o-IDTBR, a very low nonradiative voltage loss, Δ<i>V</i> _<i>nr</i> = 160 mV, is achieved, despite the presence of triplet excitons (6 × 10¹⁵ cm^-3). In employing the present system as a model exemplar, we elucidate the circumstance wherein, if the triplet lifetime surpasses the lifetime of the CT decay, the dissociation of triplet excitons to the CT state emerges as a feasible process. This, in turn, serves to reduce the manifestation of an additional loss channel from the T1 state and minimizes losses from T1. In PM6:o-IDTBR, the long triplet lifetime (10 μs) enables dissociation of the triplet state and limits the triplet-mediated recombination to ∼10%.