Researchers from Korea's Daegu Gyeongbuk Institute of Science and Technology (DGIST) developed a new way to pattern QDs, using direct optical lithography (DOL). DOL can be used to pattern QDs with ultra-high resolutions - without any photoresist.
In addition to developing this method, the researchers provided guidelines for selecting cross-linkers essential for fabricating high-performance QLEDs.
The research team introduced a diazirine-based crosslinker, TDBA, which reacts to ultraviolet light (i-line, 365 nm). TDBA possesses both a “carboxylic acid functional group” that can directly bind to the surface of QDs and a diazirine structure that responds to light. With a single light exposure, it chemically bonds to the QDs to form ultra-fine patterns. Using this approach, the team successfully achieved ultra-high-resolution patterning at about 2 μm (6,350 PPI), while also ensuring excellent precision and stability.
In addition, following the patterning process, the team applied post-treatment using a thiol-based compound called “PETMP,” which passivated surface defects on the QDs, thereby further improving their photoluminescence quantum yield (PLQY). QLED devices incorporating these post-treated QDs as the emitting layer achieved a maximum external efficiency of 10.3% and a maximum luminance of 99,369 cd/m², thereby demonstrating outstanding device performance. In addition, in semitransparent QLEDs utilizing R/G/B QDs, they verified the feasibility of double-sided emission, thus opening up possibilities for transparent display applications.