A medium bandgap dimeric acceptor with a high open-circuit voltage for efficient organic solar cells

Dimeric acceptors (DMAs) exhibit significant potential for optimizing both the efficiency and stability of organic solar cells (OSCs). However, medium band-gap DMAs with a high open-circuit voltage (V_oc) for efficient OSCs remain underexplored. In this study, we designed and synthesized a medium bandgap dimeric acceptor, designated DYO-1, through the strategy of alkoxy side-chain substitutions. The resultant DYO-1 exhibited an upshifted lowest unoccupied molecular orbital (LUMO) level and blue-shifted absorption. Notably, an o-xylene (o-XY) processed OSC with a PM6:DYO-1 binary blend achieved an ultra-high V_oc of 1.022 V and a fill factor (FF) of 73.9%, resulting in a power conversion efficiency (PCE) of 15.1%. To our knowledge, this is the highest PCE reported thus far for dimer-based OSCs with a V_oc exceeding 1.0 V. Furthermore, DYO-1 was incorporated into a PM6:L8-BO-X blend film, effectively reducing excessive aggregation of the host blend film, thus improving the carrier transport efficiency and enhancing both the short-circuit current (J_sc) and FF. Alongside the improvement in V_oc, the PM6:L8-BO-X:DYO-1 based ternary OSC, which is prepared using an o-XY solvent, achieved a prominent PCE of 19.6%. Additionally, a module device with an effective area of 13.5 cm² exhibited a PCE of 15.8%, highlighting the potential for large-area fabrications. Our study unveils the importance of medium bandgap dimeric acceptors in achieving efficient and stable OSCs, providing valuable insights into the design of high-performance electron acceptors.