A Green Co‐solvent Strategy for Morphology Control in Printable Flexible Organic Photovoltaic Modules

ABSTRACT Slot‐die coating is considered an ideal choice for the roll‐to‐roll processing of flexible organic photovoltaic (OPV) modules due to its high‐throughput processing capabilities. However, when processed in air, the solvent system and solubility characteristics jointly regulate film‐forming kinetics, posing challenges for the precise control of film morphology. Herein, we report the slot‐die coating of ultrathin flexible OPV modules using a THF:O‐XY green cosolvent, achieving an efficiency of 14.84%, one of the highest values reported for such modules. Systematic studies indicate that the superiority of the THF:O‐XY system stems from its favorable crystallization kinetics. This enables sequential nucleation of the acceptor and donor phases, leading to a uniform thin film with optimal phase separation, thereby facilitating efficient charge transport. For high‐throughput production, we extended slot‐die coating to deposit the hole transport layer, active layer, and electron transport layer, resulting in solution‐processed OPV modules. Consequently, the THF:O‐XY‐processed flexible OPV module exhibits a notable efficiency of 14.41% and a fill factor of 68.37%, both surpassing those of devices processed with pure O‐XY and THF, while also demonstrating impressive storage stability. This work offers an effective strategy for optimizing film‐forming kinetics to achieve high‐performance ultrathin flexible OPV modules.