Highly Planar Oligomeric Acceptor Enables Efficiency over 18% with Synergistically Enhanced V_OC and Light Absorption

The highly planar molecular structure is conducive to electron delocalization, thus facilitating efficient charge transport. A new thiophene terminal‐linked dimerized small‐molecular acceptor (DSMA), DTY‐2Cl, is synthesized, which achieves high planarity with a bithiophene linkage. The results of theoretical calculation and single crystal analysis of regional configuration demonstrate that the twisting angle between the bithiophene binding unit of DTY‐2Cl is almost zero. Devices based on DTY‐2Cl:D18 show an outstanding photoelectric performance with a power conversion efficiency (PCE) of 18.06% and excellent device stability. It is worth noting that DTY‐2Cl exhibits a redshifted absorption of up to 840 nm, which is rare among DSMAs, and DTY‐2Cl‐based devices obtain a VOC of 0.913 V, thus achieving a win‐win situation of redshifted absorption and high VOC. These results indicate that using bithiophene instead of biphenyl to optimize the planarity of oligomer acceptors is an effective strategy and provide a new idea for the improvement of subsequent materials.