Micrometer-scale indirect photopatterning of RGB OLED emissive layers in single phase network structure

Abstract

Organic light-emitting diodes (OLEDs) used in virtual and augmented reality displays require micrometer-scale red-green-blue (RGB) pixel patterns in the emissive layer (EML). However, conventional patterning methods based on evaporation and shadow masks can only produce patterns larger than tens of micrometers owing to the geometric constraint of the mask. Herein, an indirect method for photopatterning solution-processed OLED EMLs is proposed, which can be used to form micrometer-scale RGB pixel patterns without involving direct exposure to UV radiation or harsh etching processes on EMLs. EMLs can be patterned by i) forming a sacrificial photoresist (PR) pattern, ii) spin-coating an EML film, iii) converting the EML film into a single-phase network (SPN) structure by crosslinking vinylbenzyl-group-appended hosts and dopants at a low temperature, and iv) stripping the pre-formed PR pattern. Furthermore, repeating the process thrice results in the formation of RGB EML patterns. During the repeated process, the sacrificial PR pattern serves as a protective layer for the underlying EML pattern, effectively preventing the EML pattern from being exposed to solutions in subsequent processes. Using a conventional photolithography setup, we produced sets of RGB EML patterns with densities exceeding 3000 patterns/in., which indicated the potential of the method for industrial use.