OLED Luminaires: Device Arrays with 99.6% Geometric Fill Factor Structured by Femtosecond Laser Ablation

Abstract

The plethora of design opportunities renders organic light emitting diodes (OLEDs) ideal luminaires for general lighting applications. Progressing from lab-scale device concepts to large-area applications calls for smart device designs that are scalable and, at the same time, unsusceptible to resistive losses within the electrodes. By employing direct pulsed femtosecond laser structuring, we fabricate OLED luminaires comprising monolithically interconnected OLED arrays. We determine the laser ablation thresholds and the optimized process parameters for all functional layers. The clean laser cuts with precise ablation depths show no detectable damage to adjacent layers or any ridges, hence avoiding unwanted short-cuts or device isolation. All processes are scalable. The 3-fold structuring of the OLED luminaire is confined within 45 μm and hence below the resolution limit of the human eye, yielding a geometric fill factor beyond 99% and therefore a very homogeneous device perception.

Effect of Laser-Induced Direct Micropatterning on Polymer Optoelectronic Devices

“…The pulse duration of the laser is another important parameter for laser-induced patterning. Previous studies using lasers in OLED fabrication employed ultrafast lasers with pico- or femtosecond pulse duration to accomplish selective patterning by stress-assisted ablation. , However, the laser ablation-induced fractures and the ejection of organic or electrode materials inside the device during the fabrication process are not desirable since they can cause physical damages to the fabricated device. , Therefore, to avoid high transient thermoelastic stress during the ablation of the ITO, the polymer, and the metal electrode, we utilized a pulse duration of 100 ns, which is much longer than the reported thermal and acoustic relaxation times . Initially, we determined the optimized conditions for the laser-induced micropatterning of both PLED and PMemC devices based on polymer Super Yellow and P3HT, respectively (the detailed structures are shown in the cross-sectional SEM images in Figure S3a,c).…”

“…Inkjet printing or screen printing techniques can be employed in patterning of polymer films; however, forming an optimal formulation that can ensure both desired processability and good performance is not easily achieved. − In addition, the bank structures, which are required to keep the solution inside a given pattern, can also increase fabrication cost and complexity. For these reasons, alternative laser-induced patterning techniques (e.g., laser ablation and laser-assisted conversion) have recently gained great interest. − In a laser ablation process, an ultrafast laser was utilized to selectively remove organic layers, transparent conductive oxide layers, or top metal electrodes. , Misaki et al demonstrated 12 μm line patterns on OLED using a CO 2 laser as a localized heat source . With the help of the infrared absorbing substrate, they utilized the laser-induced thermal conversion of the precursor of N , N ′-di­(naphthalenyl)- N , N ′-di­(naphthalene-2-yl)-benzidine (α,β-TNB), and then, the unpatterned pre-α,β-TNB has to be washed out by isopropyl alcohol just like the conventional photolithography method .…”

“…For these reasons, alternative laser-induced patterning techniques (e.g., laser ablation and laser-assisted conversion) have recently gained great interest. 16−18 In a laser ablation process, an ultrafast laser was utilized to selectively remove organic layers, 17 transparent conductive oxide layers, 16 or top metal electrodes. 16,17 Misaki et al demonstrated 12 μm line patterns on OLED using a CO 2 laser as a localized heat source.…”

“…16−18 In a laser ablation process, an ultrafast laser was utilized to selectively remove organic layers, 17 transparent conductive oxide layers, 16 or top metal electrodes. 16,17 Misaki et al demonstrated 12 μm line patterns on OLED using a CO 2 laser as a localized heat source. 18 With the help of the infrared absorbing substrate, they utilized the laser-induced thermal conversion of the precursor of N,N′-di(naphthalenyl)-N,N′-di(naphthalene-2yl)-benzidine (α,β-TNB), and then, the unpatterned pre-α,β-TNB has to be washed out by isopropyl alcohol just like the conventional photolithography method.…”

“…18 Although these laser-induced techniques were able to produce micropatterning on polymer devices, the current laser patterning can only be performed at the very beginning or in the middle of device fabrication, which can limit its wide utilization in low-cost electronics due to its limited design flexibility. In particular, the patterning techniques during the fabrication process, which include conventional methods (e.g., photolithography and shadow masking) and alternative methods (e.g., coating, printing, laser ablation, 16,17 laser-assisted conversion, 18 and push-coating 19 ) are not suitable for the generation of various customized patterns upon costumers' request in low-cost electronics such as luminous packaging labels, light-emitting business cards, and disposable name tags. This is because the final pattern is determined by the mask design.…”