Breaking 20% Efficiency of all‐Polymer Solar Cells via Benzo[1,2‐d:4,5‐d′]Bisthiazole‐Based Terpolymer Donor Strategy for Fine Morphology Optimization

Developing high‐performance all‐polymer solar cells (all‐PSCs) remains a challenge due to the difficulty in controlling the morphology of polymer blends. In this study, benzo[1,2‐d:4,5‐d′]bisthiazole (BBTz) is incorporated into the PM6 main chain to create a series of terpolymer donors, leveraging the entropy increase and superior miscibility with polymer acceptors to modulate blend morphology. The introduction of BBTz broadened the absorption range, enhanced film crystallinity, and significantly improved donor‐acceptor miscibility through its low dipole moment and high electrostatic potential. This facilitated the formation of nanofiber structures in the active layer, thus optimizing blend morphology. As a result, the PBZ‐10:PY‐IT‐based device achieved an impressive power conversion efficiency (PCE) of 19.06%. Incorporation of PBQx‐TF into the binary blend can further improve morphology, charge transport, exciton lifetime, charge dissociation, and collection, as well as suppressed charge recombination, finally leading to a record‐breaking PCE of 20.04% for all‐PSCs to date. The findings demonstrate the effectiveness of the terpolymer strategy in enhancing all‐PSC performance. By optimizing molecular design and component selection, this approach provides a viable pathway for achieving higher efficiency all‐PSCs and supports the advancement of renewable energy technologies.