A double-cable Y-series-based polymer acceptor for efficient all-polymer solar cells: a new strategy of polymerizing small molecule acceptors

Abstract

Further advancement of all-polymer solar cells (all-PSCs) requires a new polymerization design strategy to develop ideal polymer acceptors that possess and retain maximally the advantages of narrow bandgap non-fullerene acceptor building blocks. In this work, we report a new design strategy to synthesize a polymerized small molecule acceptor PT-BTP with a double-cable structure composed of a fused-ring Y-series acceptor framework as a pendant side unit and thiophene derivative as the conjugated backbone. PT-BTP exhibits a narrow optical bandgap of 1.35 eV and high electron mobility as well as a favorable BHJ blend morphology when blended with polymer donor PM6, resulting in good photovoltaic performance. The optimized PM6:PT-BTP all-PSCs displayed a high PCE of 12.13% with an energy loss (E_loss) of 0.566 eV and a small non-radiative recombination loss (ΔE₃) of 0.227 eV. In contrast, the as-cast devices only showed a lower PCE of 8.14% with inferior E_loss and ΔE₃ values. This work enables a new molecular design direction to construct narrow bandgap P_As toward successful applications in high-performance all-PSCs.