Efficient Large Area All-Small-Molecule Organic Solar Cells Fabricated by Slot-Die Coating with Nonhalogen Solvent

The commercialization of organic solar cells (OSCs) requires the use of roll-to-roll coating technology. However, it is generally believed that all-small-molecule (ASM) systems cannot form high-quality films in most film-fabrication technologies except for spin coating, mainly due to their strong crystallinity and low solution viscosity. Herein, it is found that the small molecule donor and acceptor system with strong intermolecular interaction can weaken the molecular self-aggregation during film formation. As a result, all-small-molecule organic solar cells (ASM-OSCs) are successfully fabricated using the green solvent tetrahydrofuran via spin coating as well as slot-die coating technology. Under the optimal conditions, the devices achieve power conversion efficiency (PCE) of 14.05% and 13.41% prepared by spin coating and slot-die coating, respectively. Moreover, a large-area device with an area of 1 cm(2) achieve a PCE of 10.65% by slot-die coating. The study of the device performance and the active layer morphology reveal a unique film optimization mechanism in ASM-OSCs. In the slot-die coating process, a high-quality film is formed due to the significantly suppressed crystallinity of the small molecule donor; with further thermal annealing, the crystallization-induced phase separation enables an optimized morphology. This study proves that high-performance ASM-OSCs can be fabricated by the industrial-compatible method.