Slot‐Die Coating of All Organic/Polymer Layers for Large‐Area Flexible OLEDs: Improved Device Performance with Interlayer Modification

Abstract Organic light‐emitting diodes (OLEDs) fabricated on flexible transparent substrates have found application in displays, lighting, and signage. Optimization of the fabrication procedures is critical for commercialization to maximize performance and reduce costs. Utilization of the slot‐die coating technique, a solution‐processing roll‐to‐roll method, has emerged as a viable method to manufacture flexible OLED devices. Here, the fabrication of flexible OLEDs via the slot‐die coating technique under ambient condition is reported. The OLEDs have a simple architecture of polyethylene terephthalate (PET)/indium–tin oxide (ITO)/hole injection layer (HIL)/emissive layer (EML)/electron injection layer (EIL)/Ag, where poly(3,4‐ethylenedioxythiophene):polystyrene sulfonate (PEDOT:PSS) is used as the HIL, Super Yellow (SY, poly(1,4‐phenylenevinylene) copolymer) is used as the EML, and poly((9,9‐bis(3′‐(N,N‐dimethylamino)propyl)‐2,7‐fluorene)‐alt‐2,7‐(9,9‐dioctylfluorene)) (PFN) is used as the EIL. The optimization of the PFN layer using slot‐die coating technique is focused by varying solvent, solvent additives, substrate temperature, and coating speeds. The OLEDs that have PFN layers processed with the known solvent additives, 1,8‐diiodooctane (DIO) or diphenyl ether (DPE), show a performance increase compared to OLEDs based on PFN layers processed with no solvent additives. Finally, large‐area multicolor OLEDs are constructed with organic/polymer layers being slot‐die coated in sequence, of which all display homogeneous luminance under bending/folding conditions, highlighting the potential of this simple device structure and processing method.