Synergistic effect of two complementary acceptors assists high-efficiency as-cast organic solar cells

As-cast organic solar cells (OSCs) with great potential for low-cost commercial production are still in the backward stage of development. Herein, two small-molecule acceptors Y6 and Y6-1O with similar chemical structures were combined with polymer donor D18 to fabricate as-cast OSCs. The two highly compatible acceptors possess complementary bandgaps and energy levels, which contribute to achieving an optimal balance between the short-circuit current density and open-circuit voltage in ternary OSCs by modulating the Y6/Y6-1O ratio. Moreover, film-formation dynamics, morphological, and theoretical explorations reveal that the easily clustered Y6-1O shows a larger binding energy with D18 than that of the group of Y6 and D18, leading to a faster film-formation process of the active layer. Manipulating the Y6-1O content in the ternary matrix can effectively control the aggregation of D18 by shortening the film-formation time, and then forming profitable film morphology for efficient exciton dissociation, charge transport, and collection, thus reducing the energy loss and improving the fill factor of the device. Consequently, the synergistic effect of two acceptors results in the as-cast ternary device achieving a top-ranked power conversion efficiency (PCE) of 19.51%. This work demonstrates an effective approach with the ternary strategy to construct high-performance as-cast devices.