Three-Dimensional Photo-Cross-Linkers for Nondestructive Photopatterning of Electronic Materials

Abstract

Solution-processed electronics have shown promise in cost-effective manufacturing, but face challenges in precisely and accurately placing electronic materials. Traditional methods, such as photolithography with photoresists, involve complex steps that can damage electronic materials. Alternatives such as orthogonal patterning and inkjet printing are limited by the difficulty of finding compatible chemicals that do not dissolve underlying layers, while nanoimprinting lacks compatibility with high-throughput processes and suffers from poor chemical robustness. Conventional photo-cross-linking approaches have used organic or polymeric agents to pattern electronic layers, but the consecutive application of photo-cross-linking processes for patterning and stacking of multiple electronic materials typically led to degradation of the intrinsic properties of the materials.

To overcome these issues, we have demonstrated a promising photopatterning strategy of using highly efficient, three-dimensional photo-cross-linkers bearing multiple phenyl azides. Specifically, electronic materials hosting a minimal amount of the photo-cross-linkers were photo-cross-linked under UV through a photomask, followed by subsequent removal of the uncross-linked parts using a developing solvent. This method produces a patterned electronic layer that maintains chemical and physical stability while enhancing the thermal and mechanical stabilities. The successive patterning of electronic materials in this approach has precise control over parallel or vertical stacking of high-resolution electronic material layers without optical/electrical property loss. This Account provides an overview of our efforts toward photopatterning electronic materials in the field of polymer thin film transistors (PTFTs), organic light-emitting diodes (OLEDs), and quantum-dot light-emitting diodes (QD-LEDs). First, two azide-based multibridged photo-cross-linkers (i.e., 4Bx and 6Bx) were developed and applied to fabricate all-solution-processed PTFTs. These cross-linkers have excellent cross-linkability compared to a conventional bifunctional photo-cross-linker (i.e., 2Bx), leading to fabricating thin-film electronic layer patterns and acquiring chemical resistance of each layer. Moreover, they effectively reduce leakage current and enhance the electrical strength in dielectric layers. This research underscores the crucial role of efficient cross-linkers in achieving all-solution-processed, all-photopatterned organic electronic devices while preserving their intrinsic electrical properties of employed semiconducting polymers. These cross-linkers have also been applied for OLEDs, which produces high-resolution photopatterned light-emitting polymer semiconductors. Furthermore, azide-based photo-cross-linking chemistry has been applied to the patterning of luminescent QDs. A breakthrough approach of utilizing a bulky isopropyl group-containing photo-cross-linker (i.e., IP-6-LiXer) has been demonstrated to form high-fidelity patterns of heavy-metal-free QDs to realize high-resolution full-color QD-LEDs. IP-6-LiXer allows efficient photo-cross-linking between QDs without harming the optical/electrical properties of QDs. The six azide groups at its terminals cross-link the QDs by forming covalent bonds selectively with the ligands on the QD surfaces. The isopropyl groups in IP-6-LiXer inhibit the undesirable chemical contact between azide groups and core metals in the QDs. This characteristic of these cross-linkers leads to nondestructive direct photopatterning of luminescent heavy-metal-free QDs. Lastly, we conclude that our approaches have been effective across various electronic materials, including polymers and QDs, emphasizing the versatility and potentials in the various optoelectronic devices.