Abstract
Orthogonal processing is a photolithographic patterning method using fluorous solvents and highly fluorinated photoresists; it has shown potential as a unique patterning protocol that can form high-resolution structures while minimizing damage to the thin films of organic electronic materials. In this study, we adopted the technique to the photo-patterning of 15 μm half-pitch organic light-emitting diode (OLED) pixels on a 4,4′,4»-tri(N-carbazolyl)triphenylamine (TCTA) thin film that forms a hole-transporting layer (HTL). However, the device patterned using the highly fluorinated materials system showed a lower driving voltage and reduced efficiency compared to the non-patterned device. This problem was presumed to be caused by the attachment of strong acid molecules generated from the photo-patterning process and residues of the highly fluorinated photoresist to the TCTA surface. To remove this scum layer and to restore the performance of the TCTA, a solution-based rinsing process was devised and performed onto the TCTA layer by adding a trace amount of (dimethylamino)trimethylsilane (DMTS) and tris(trimethylsilyl)silane (TTMSS) to a fluorous solvent. As a result, the driving voltage and efficiency of the patterned OLED device were restored to similar levels to those of the non-patterned reference. Observation of the patterned TCTA layer with an atomic force microscope (AFM) gave an idea that the morphology of the patterned TCTA film was changed to be similar to that of the pristine TCTA film after the solution-based rinsing process. Furthermore, X-ray photoelectron spectroscopy (XPS) also verified that the solution containing descumming agents reduced the fluorine residue on the TCTA surface. This result demonstrated that the solution-based descumming process is an effective approach to increase the device performance during the photolithographic patterning of OLEDs to which typical dry etching-based descumming may not be applied.
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