Abstract
Nowadays, the display industry is endeavoring to develop technology to provide large-area organic light-emitting diode (OLED) display panels with 8K or higher resolution. Although the selective deposition of organic molecules through shadow masks has proven to be the method of choice for mobile panels, it may not be so when independently defined high-resolution pixels are to be manufactured on a large substrate. This technical challenge motivated us to adopt the well-established photolithographic protocol to the OLED pixel patterning. In this study, we demonstrate the two-color OLED pixels integrated on a single substrate using a negative-tone highly fluorinated photoresist (PR) and fluorous solvents. Preliminary experiments were performed to examine the probable damaging effects of the developing and stripping processes upon a hole-transporting layer (HTL). No significant deterioration in the efficiency of the develop-processed device was observed. Efficiency of the device after lift-off was up to 72% relative to that of the reference device with no significant change in operating voltage. The procedure was repeated to successfully obtain two-color pixel arrays. Furthermore, the patterning of 15 μm green pixels was accomplished. It is expected that photolithography can provide a useful tool for the production of high-resolution large OLED displays in the near future.
Highlights
The display industry has been evolving from liquid crystal displays (LCDs) towards organic light-emitting diode (OLED) technology that can implement paper-thin displays with excellent viewing angle and more vivid colors, and OLED has successfully entered the commercialization stage
A shadow mask composed of a thin metal plate and tiny holes perforated on it (FMM) is positioned below a substrate in a vacuum chamber, and electrically active layers, including a light-emitting layer (EML) of the desired color, is deposited only at the open regions of the FMM
The emitting area was not defined by the PDL pattern on the indium tin oxide (ITO), but by the photo-patterned EML itself on the common hole-transporting layer (HTL)
Summary
The display industry has been evolving from liquid crystal displays (LCDs) towards organic light-emitting diode (OLED) technology that can implement paper-thin displays with excellent viewing angle and more vivid colors, and OLED has successfully entered the commercialization stage. A shadow mask composed of a thin metal plate and tiny holes perforated on it (FMM) is positioned below a substrate in a vacuum chamber, and electrically active layers, including a light-emitting layer (EML) of the desired color, is deposited only at the open regions of the FMM This means that the holes on the mask must be extremely small and densely assembled if an ultra-high-resolution display is to be fabricated using the FMM method. Photolithography with its high-resolution capabilities and well-established registration method is the only reliable patterning tool for integrated circuits in the semiconductor industry This technical benefit motivated several research groups to apply it to OLED pixel patterning. This result strongly implies that OLED pixel-patterning using photolithography can be a promising candidate applicable to the production of high-resolution display panels
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