Heat-Assisted Direct Photopatterning of Small-Molecule OLED Emitters at the Micrometer Scale

Abstract

A crucial step in fabricating full-color organic light-emitting diode (OLED) displays is patterning the emissive layer (EML). Traditional methods utilize thermal evaporation through metal masks. However, this limits the achievable resolution required for emerging microdisplay technologies. Alternatively, direct photolithography, wherein the layer to be patterned serves as a photoresist, offers a cost-effective method for producing high-resolution displays. Direct photopatterning methods for small molecules used as EMLs in OLEDs are introduced. This method employs photopolymerizable vinylbenzyl moieties directly anchored to the host and dopant small-molecule emitters. By photoinitiating a free radical polymerization reaction between the vinylbenzyl moieties under mild annealing conditions (60 °C), the EML can be photopatterned using an i-line UV source. Mild annealing is critical for achieving polymerization reactions at a low UV irradiation dose (0.6 J cm⁻²) without degrading the luminescent properties of the emitters. This process is referred to as heat-assisted direct photopatterning (HADP). Using HADP, red, green, and blue OLED emitters with a minimum pattern width of 2 µm are successfully fabricated. These OLED emitters can be patterned side-by-side by simply repeating the patterning steps three times. This method offers a promising alternative for producing patterns of small molecules desired for ultrahigh-resolution OLED-based microdisplay technology.