Dual-Step Solvent Vapor Annealing for Improved Morphology Control in Sequentially Deposited Organic Solar Cells

Sequential deposition (SD) processing offers advantages for morphology optimization of active layer and device stability in organic solar cells (OSCs). However, the insufficient solvent resistance of polymer donor layers often leads to uncontrolled interfacial mixing. Herein, we report a dual-step solvent vapor annealing (D-SVA) strategy to address this limitation, without requiring thermal annealing, making it suitable for ultrathin flexible OSCs. Sequential chlorobenzene (CB) and carbon disulfide (CS2) vapor treatments enhance the molecular ordering and solvent resistance of the underlying donor layer, while reducing residual solvent and improving interfacial properties. As a result, the rigid SD processed OSCs achieve a power conversion efficiency (PCE) of 19.3%. Moreover, ultrathin flexible devices deliver a PCE of 17.3% with good mechanical stability. This work provides a general and scalable pathway toward high-performance and stable SD organic solar cells.