Enhancing efficiency and stability of non-fullerene organic solar cells via volatilizable solid-liquid-mixed additive system

While traditional high-boiling-point liquid additives like 1,8-diiodooctane (DIO) and 1-chloronaphthalene (CN) et al. are commonly used, here we explore the potential of solid additives to optimize organic solar cells (OSCs) performance. Thieno[3,2-b]thiophene (TT), a volatilizable solid additive (VSA), is introduced into the PM6:Y6 OSCs system. TT's similarity to the Y6 backbone allows it high miscibility with Y6 molecules. In light of the fully volatile property, TT induces more uniform and condensed intermolecular packing of the active layer. This refinement increases the power conversion efficiency (PCE) from 14.45% to 15.31%. To further optimize morphology, TT is combined with the liquid additive CN, creating a binary liquid-solid additive system. This combination promotes favorable nanoscale phase separation within the PM6:Y6 active layer. Overall, the OSCs processed with TT+CN achieve an impressive efficiency of 16.43%, attributed to improved charge transport and reduced exciton recombination losses from the dual additives' synergistic effects. Importantly, the OSCs processed with TT demonstrate enhanced long-term stability, retaining 89.5% of their initial performance after 30 days, outperforming devices without additives (87.3%) and those processed with CN alone (80.5%). In summary, this research introduces TT as a promising volatilizable solid additive and a rational additive strategy to manipulate active layer film morphology. These advances hold significant potential for developing high-efficiency and stable OSCs, contributing to sustainable energy solutions.