Lift-Off Patterning of OLED Active Layer

Active layer patterning of organic light-emitting diode (OLED) is a key step in achieving full-color display application. Although conventional OLED manufacturing is based on thermal evaporation, solution process-based patterning techniques allows low-cost fabrication of large-area display. In this work, we propose a patterning method for OLED active layer done via a lift-off process. The lift-off process is widely used in conventional semiconductor and display industry, but its applications to OLEDs are limited. This is due to the fundamental issue that process solvents (such as stripper) can dissolve/damage the pre-deposited layer that should be partially lifted-off. In particular, the luminescent small molecules of OLED (such as iridium and platinum complexes) are assembled by weak forces. Herein, we present the use of crosslinkable host and guest organic emitters added with a low-temperature thermal initiator serving as the active layer for OLEDs. The thermally crosslinked active layer shows chemical robustness against subsequent solvent-processes without compromising its luminescence characteristics (indeed we found that the luminescence characteristics are improved upon crosslinking the molecules). More importantly, by initiating the crosslinking reactions below the temperature affecting the chemical/structural properties of photoresist, we can apply the crosslinked active layer to conventional lift-off process to form active layer patterns. Based on this, we successfully fabricate a few microns multicolor patterns with a minimum pattern width of 4um and exceptionally low line-width roughness. We believe that this approach suggests an alternative route to form micrometer-scale patterns of solution processible materials.