Construction of High-resolution Patterns of Solution-processed Organic Light-emitting Diodes Using Surface Modified Banks by Wettability

Abstract

In the field of flat-panel displays, solution-processed organic light-emitting diodes (S-OLEDs) have attracted considerable attention due to the applicability of low-cost, low-temperature, and large-area processes. For manufacturing S-OLEDs, much effort has been made toward the development of simple and reliable methods of patterning individual elements of the S-OLEDs. One of widely used techniques for patterning a solution is based on insulating banks to define solution patterns without any detrimental effect on the device performances. However, it suffers intrinsically from the pattern resolution as well as the pattern fidelity since the formation of high-density insulating banks on a substrate significantly deteriorates the wetting nature of a solution. Thus, the delicate control of the surface wettability of a bank-structured substrate (BS) is inevitably required for achieving the high level of the pattern resolution and fidelity of the solution. This study presents a viable method of producing high-resolution patterns for pixels in the S-OLED with the aid of ultraviolet ozone (UVO) treatment on the BS. The insulating banks were first prepared through the injection of photo-curable polymer (NOA 74) into the channels between a pre-patterned polydimethylsiloxane (PDMS) stamp and an indium-tin-oxide (ITO)-coated glass substrate by capillary action and subsequently cured under the ultraviolet (UV) light. The modification of the surface wettability of the BS was carried out by the UVO treatment as a function of time. From the results for the contact angles of the water, the surface of the BS was found to be greatly modified from hydrophobic surface to hydrophilic surface with increasing the treatment time. Using the insulating banks of 5 μm and 10 μm in line width and space, the corresponding S-OLEDs patterns were fabricated with high resolution. Also, S-OLED was fabricated with identical fabrication method on the flexible substrate which is one of the features of next generation display. This wettability-controlled patterning approach will provide a useful platform to construct next generation displays from solutions in the manner of high resolution over large area and low cost.