π‐Extended Conjugated Polymer Acceptor Containing Thienylene–Vinylene–Thienylene Unit for High‐Performance Thick‐Film All‐Polymer Solar Cells with Superior Long‐Term Stability

Abstract Despite the rapid developments in all‐polymer solar cells (all‐PSCs) due to the progress of polymerized small molecular acceptors (PSMA), the effect of linkage unit conjugation on the polymer acceptor (P A ) is not well understood and P A s with high efficiency, good stability, and thickness‐insensitivity are rarely seen. Herein, two novel PSMAs, named PJTVT and PJTET are designed, by incorporating conjugated thienylene‐vinylene‐thienylene (TVT) and unconjugated thienylene–ethyl–thienylene (TET) units, respectively. Results show that the energy levels, energy losses, and energy offset of the two PSMAs have little difference ( <≈ 0.03 eV). However, due to the π‐extended coplanar backbone of PJTVT, when blended with polymer donor JD40, a more ordered π–π stacking and enhanced face‐on orientation morphology is observed, which contributes to enhanced exciton dissociation, superior charge transport, and faster charge extraction, leading to a record power conversion efficiency of 16.13% (10.93% for JD40:PJTET). Impressively, the JD40:PJTVT device shows superior thickness‐insensitivity and long‐term stability, both of which make it an ideal choice for industrialization. These results demonstrate that molecular modulation in the linking unit is a promising strategy to construct PSMAs for high‐performance thick‐film all‐PSCs with superior long‐term stability, and shows the superiority of conjugated backbones for PSMAs.