Improving efficiency and flexibility of non-halogenated solvent-processed dual-layer organic solar cells through solvent vapor annealing

Dual-layer organic solar cells (OSCs), fabricated through sequential-casting with separately dissolved donor and acceptor materials, offer simplified solution preparation and morphology control. However, the poor solubility of organic materials in non-halogenated solvents often results in undesirable vertical component distribution and insufficient donor/acceptor interfaces in non-halogenated solvent-processed dual-layer OSCs, adversely affecting photovoltaic performance and flexibility. In this study, we applied a solvent vapor annealing (SVA) method using CS₂ solvent in o-xylene solvent-processed dual-layer OSCs. The SVA method effectively adjusted the vertical component distribution of the active layer and increased the donor/acceptor interfaces, leading to an improved power conversion efficiency (PCE) of 17.24 %. Additionally, SVA films exhibited superior tensile properties, with a crack onset strain of 5.07 %, surpassing that of the as-cast films (4.32 %), attributed to the stronger interaction between the donor and acceptor layers with more donor/acceptor interfaces. Consequently, large-area (1 cm²) flexible devices achieved a significant efficiency of 14.20 % and maintained excellent mechanical flexibility, with 80 % of the initial efficiency retained after 1000 bending cycles. This work presents an effective approach for fabricating high-performance non-halogenated solvent-processed flexible dual-layer OSCs.