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.

Water-Processable Self-Doped Hole-Injection Layer for Large-Area, Air-Processed, Slot-Die-Coated Flexible Organic Light-Emitting Diodes

“…The KPFM analysis allowed for the quantification of V CPD between the conductive AFM tip and the PEDOT:PSS and P2 samples, with a Ag film serving as the reference sample. The obtained work function of PEDOT:PSS is consistent with previously reported values in our earlier studies. , The results reveal a slightly lower energy barrier for hole injection into P2 (−0.3 eV) compared with PEDOT:PSS (−0.5 eV), as demonstrated by the measured work function values. These negative values indicate favorable conditions for hole injection, with the smaller value indicating a more favorable scenario.…”

“…In our prior work, we have reported the optimized thicknesses, along with their corresponding coating and curing conditions, for large-area slot-die-coated materials including PEDOT:PSS, PVK, SY, and PFN under ambient air conditions. 19,20 Figure 4a−c presents the current density (mA/cm 2 ) vs voltage (V), luminescence (cd/m 2 ) vs voltage, and current efficiency (cd/A) vs luminance (cd/m 2 ) characteristics of champion OLEDs with P2 and PEDOT:PSS HILs, respectively. Table 1 provides an overview of the statistical analysis for five champion devices.…”

“…20 Among the approaches tested, the PFN films processed from alcohols with the solvent additive diphenyl ether (DPE) showed the best performance, with a turn-on voltage of 5.5 V, maximum luminance of 2500 cd/m 2 , and maximum current efficiency of 1.0 cd/A for a 1.6 cm 2 emissive area. 20 Our results represent an advanced example of all-organic layer OLEDs fabricated using slot-die coating. HILs in large-area ambientprinted OLEDs have been less explored compared to electron injection layers and emissive materials, mainly because of resource limitations and various challenges.…”

Thiochromenocarbazole imide: a new organic dye with first utility in large area flexible electroluminescent devices

“…As the field of printed organic electronics has evolved it has become critical to evaluate new materials as large area films fabricated via relevant high-through-put coating methods. 45–48 Hence, with good film forming capacities and solubility in industrially compatible solvent and promising performances in conventional devices, TCI 2 was evaluated in large area flexible devices using the roll-to-roll compatible slot-die coating method (Fig. 9).…”

Room-Temperature Photodeposited Amorphous VOx Hole-Transport Layers for Organic Devices

“…Using a combination of UV−vis and UPS, it is possible to estimate the energy levels of the system (Figure 4; see Figure S15 for OLED devices 49 ). The only level to significantly change upon annealing VO-AP to VO-250 is the bandgap value, resulting in a higher conduction band minimum for VO-250.…”