Development of Crosslinkable Emitters for Micropatterning the Emissive Layer in Solution-Processed Organic Light-Emitting Diodes

Organic light-emitting diodes (OLEDs) are one of the most successful commercial display technologies, and they are continuously being developed for use in next-generation devices, including ultrahigh-resolution near-eye displays for virtual reality (VR) and augmented reality (AR) systems. To apply OLEDs to VR and AR, micrometer-scale red-green-blue (RGB) pixel patterning in the emissive layer (EML) is a key step for achieving high-resolution full-color OLED displays that deliver high-quality images to users. However, conventional patterning methods based on evaporation and shadow masks can only produce patterns larger than tens of micrometers due to the geometric constraints of the mask. In this presentation, we present the indirect photopatterning of micrometer-scale RGB EMLs in a single-phase network (SPN) structure. The SPN structure consists of a chemically crosslinked network of host and dopant molecules, exhibiting excellent chemical resistance to various solvents. This structure can be formed using crosslinkable organic luminophores as both dopant and host materials. To implement the SPN structure, we designed and synthesized a red-emitting iridium complex (Ir(btpy)₃-V3), a green-emitting iridium complex (Ir(ppy)₃-V3), and a blue-emitting thermally activated delayed fluorescence emitter (TRTz-V2). These dopants were modified to include vinylbenzyl groups for crosslinking. Additionally, we employed a host material, CBP-V2, which also incorporates vinylbenzyl groups. The vinylbenzyl groups in both the dopants and the host material enable thermal crosslinking at a low temperature (<120 °C) in the presence of an azobisisobutyronitrile (AIBN) radical initiator. Using these crosslinkable dopant and host molecules, we performed indirect photopatterning of RGB EML by repeating the following steps: i) forming a sacrificial PR pattern, ii) spin-coating an EML film comprising dopant and host molecules, iii) converting the EML into the SPN structure through crosslinking, and iv) stripping the PR pattern. The dimensions of the resulting EML patterns were determined by the shape of the PR pattern utilized. Notably, this approach enables the formation of EML patterns without direct exposure of the material to UV radiation or any harsh etching process. Additionally, the underlying EML patterns are protected from degradation and contamination during the multicolor EML patterning process. Using the proposed indirect photopatterning method, we successfully fabricated EML patterns in both linear and circular shapes. RGB full-color EML patterns were achieved by sequentially repeating the patterning process with RGB crosslinkable emitters and a crosslinkable host. Notably, the circular RGB patterns demonstrated an impressive pattern density, exceeding 3000 patterns per inch. We emphasize that the entire process was conducted using a conventional photolithography setup. The indirect photopatterning method holds significant promise for realizing micrometer-scale, high-resolution RGB OLED displays.