Additive-Free All-Green Solvent-Processed Efficient and Stable Pseudo-Bilayer Bulk Heterojunction Ternary Organic Solar Cells

Most effective pseudo-bilayer planar heterojunction (PPHJ) devices, which facilitate vertical phase separation, often depend on toxic halogenated solvents in the production process. However, obtaining the desired morphology poses a significant challenge when utilizing nonhalogenated solvents due to the limitations of material solubility and unfavorable kinetics of film forming. The cooperative effect between the exciton dissociation and the exciton diffusion distance in PPHJ devices could be enhanced by accurate regulation of the donor: acceptor heterojunction. Hence, the pseudo-bilayer bulk heterojunction (PBHJ) strategy approach was used because of its process involving a dilute solution, aiming at optimizing phase formation kinetics and achieving a rational vertical components distribution in all-green o-xylene (o-XY) processed ternary organic solar cells (OSCs). In this study, a comprehensive analysis of charge recombination and carrier dynamics was conducted in three device structures: bulk heterojunction (BHJ), PPHJ, and PBHJ. It was found that the PBHJ device demonstrated enhanced charge generation, extended exciton lifetime, and reduced nongeminate charge recombination. Finally, the ternary PBHJ device based on PM6:BTP-eC9:L8-BO achieved a photovoltaic efficiency of 18.30%, significantly higher than those of the corresponding BHJ devices (17.38%). It is worth noting that the ternary PBHJ device exhibited excellent stability with 91.79% of the initial power conversion efficiency (PCE) retained after continuous illumination for 1 h under maximum power point (MPP) tracking, and the stability in the glovebox could still retain 92.55% of the initial PCE after 2700 h. This study provides valuable insights into optimizing the active layer phase separation and providing sufficient charge transport channels, thus improving the device stability.

Automated summary

This study presents the use of a pseudo-bilayer bulk heterojunction strategy to optimize the active layer morphology in ternary organic solar cells. The resulting PBHJ device exhibits enhanced charge generation, extended exciton lifetime, reduced charge recombination, and improved stability compared to other device structures.