Bithiazole derivative as a solid additive endows organic solar cells with enhanced photovoltaic performance

Abstract

The dual-additive strategy, which combines solid additives and solvent additives, holds great promise yet remains challenging for synergistically optimizing the molecular orientation and crystalline behaviors of photoactive materials. Herein, a newly designed solid additive, 5,5′-bis(dimethoxymethyl)-2,2′-bithiazole (BTz) was synthesized. Characterized by a rigid planar structure and uneven electron distribution, BTz has robust molecular interaction with non-fullerene acceptors, which effectively optimized the crystallinity and molecular stacking of Y6. By combining the traditional solvent additive 1-chloronaphthalene (CN), the dual-additive approach facilitated more ordered self-assembly of the acceptors in the blend films with bi-continuous interpenetrating networks. The morphology optimization of the active layer promoted more efficient charge dynamics and synergistically enhanced the key photovoltaic parameters of the devices, including open-circuit voltage, short-circuit current and fill factor. Compared to the benchmark devices processed with CN alone, the additional incorporation of BTz boosted the power conversion efficiencies of PM6:Y6-, PM6:L8-BO- and D18:L8-BO-based systems to 19.02 %, 19.58 % and 20.04 %, respectively, which implies the effectiveness and universality of the dual-additive strategy in optimizing the performance of non-fullerene organic solar cells.