Heat-Assisted Direct-Photolithography of Small Molecule Emitters

Patterning the emissive layer is a crucial step in fabricating full-color organic light-emitting diode (OLED) displays. Traditional manufacturing relies on thermal evaporation, but using fine metal masks limits achievable resolution that is required for emerging microdisplay technology. Alternatively, direct photolithography, where the layer to be patterned acts as a photoresist, offers a time- and cost-effective method for producing high-resolution displays. In this study, we introduce a direct photopatterning method for organic small molecules used in OLED emissive layers. To photopattern the layers, our method employs a photo-crosslinkable vinyl benzyl moiety directly anchored the host and guest organic small molecule emitters. By photoinitiating a free radical polymerization reaction between the vinyl benzyl moieties under mild annealing conditions (60°C), the emissive layer can be photopatterned using an i-line UV source (wavelength: 365 nm) without degrading its luminescent properties. Here, mild annealing was critical for achieving thorough crosslinking of the emissive layer, where no crosslinking occurred without it. Thus, we refer to this process as heat-assisted direct photopatterning (HADP). Using HADP, we successfully fabricated patterns of red, green, and blue OLED emitters with widths of a few microns achieving a minimum pattern width of 2 µm. We believe this method offers a promising alternative for producing microscale patterns with organic small molecules, which is in high demand for ultrahigh-resolution OLED-based microdisplay technology.