Desired open-circuit voltage increase enables efficiencies approaching 19% in symmetric-asymmetric molecule ternary organic photovoltaics

The large open-circuit voltage (Voc) loss is currently the main obstacle for pursuing the highly efficient organic photovoltaics (OPVs). To address this issue, we construct the ternary OPVs (TOPVs) consisting of symmetric BTP-eC9 and asymmetric BTP-S9 acceptors with similar absorption profiles and demonstrate it as a feasible way to increase Voc via reducing the energetic disorder and non-radiative decay. This strategy enables a desired higher voltage in TOPVs than those in both binary OPVs, without sacrificing absorbing range. Besides, the ternary blend exhibits enhanced charge transport property due to stronger π-π stacking than binary films, resulting in the enhanced fill factor (FF). Consequently, the optimal TOPV exhibits a champion efficiency of 18.8% (certified as 18.7%) with a high voltage of 0.861 V and a high FF of 79.34%, representing the best among certified single-junction OPVs. This work demonstrates an effective approach to increase Voc, paving the way toward high-efficiency OPVs.