Bithieno[3,4- c]pyrrole-4,6-dione-mediated crystallinity in large-bandgap polymer donors directs charge transportation and recombination in efficient nonfullerene polymer solar cells

Solution-processed nonfullerene bulk-heterojunction (BHJ) polymer solar cells (PSCs), which are composed of polymer donors and organic acceptors, are proven to manifest promising performance and long-term stability. In this concise contribution, bithieno[3,4-c]pyrrole-4,6-dione (BiTPD), which is a TPD derivative but presents a large planar structure and strong electron-withdrawing ability, was used to construct a large-bandgap polymer donor PBiTPD. Results show that the polymer donor PBiTPD realized power conversion efficiency (PCE) as high as 14.2% in fullerene-free BHJ solar cells. Larger ionization potential value, more favorable face-on backbone orientation, and stronger crystallinity were concurrently obtained in PBiTPD. Correspondingly, improved and more balanced charge transportation; less nongeminate and trap-assisted recombination losses; and thus high fill factor (FF) of 67%, short-circuit current density (J_SC) of 25.6 mA·cm^-2, and high open-circuit voltage (V_OC) of 0.83 V were concurrently achieved in PBiTPD-based devices. PBiTPD does clear the way for a novel and promising class of large-bandgap polymer donor candidates.