Densely Packed Random Quarterpolymers Containing Two Donor and Two Acceptor Units: Controlling Absorption Ability and Molecular Interaction to Enable Enhanced Polymer Photovoltaic Devices

Dithienyldiketopyrrolopyrrole (DPP2T) and thieno[3,2‐b]thiophene (TT) building blocks, enabling a large intermolecular overlap through π–π stacking, into an amorphous‐like polymer composed of benzo(1,2‐b:4,5‐b′)dithiophene (BDT) and fluorinated thieno[3,4‐b]thiophene (QTT), are introduced. Herein, through the variation of relative compositions of DPP2T‐TT and BDT‐QTT in the polymer backbone, the synthesis and characterization of a series of condensed random 2D‐2A “quarterpolymers” with two reference alternating copolymers are reported. The best power conversion efficiency (PCE) of 9.45% is achieved for the optimum composition due to the synergistic effects such as improved photon absorption and reduced recombination loss, and optimized blend morphology via a change in the crystallinity and orientation of the blend films compared to the alternating copolymers. Moreover, by isolating higher molecular weight and narrower polydispersity fractions of the quarterpolymer via a marginal solvent‐soaking technique, the PCE is further boosted to 10.30%, which is among the highest PCE reported to date for random polymer‐based PSCs. Therefore, this simple 2D‐2A strategy, reported for the first time, should be extended to numerous quaterpolymer systems, greatly accelerating random polymer systems toward further improving PSCs.