Effects of the surface ligands of quantum dots on the intaglio transfer printing process

Abstract

High-resolution semiconductor nanocrystal quantum dot (QD) patterns are required for applications in display devices. For this, the dry transfer printing of QDs is promising because it does not degrade the inherent properties of QDs. However, the effect of the surface ligands on this process remains poorly understood, despite its importance. Herein, we investigate the effect of the surface ligands on the intaglio transfer printing process. Colloidal QDs with organic (C8–C18) or inorganic (I−) ligands are prepared. In various pattern-printing tests, including patterns with a sub-10-μm width, the patterning yield is ∼100% for QDs with long-chain ligands (C18). However, the patterning yield decreases with decrease in the chain length for the organic-ligand-passivated QDs and is the lowest for the QDs passivated with I−. Using surface energy characterization and finite element method simulations, we suggest two printing failure mechanisms: (i) Inorganic-ligand-passivated QDs are not effectively picked-up by the stamp because of poor adhesion, and, (ii) for the organic-ligand-passivated QDs, internal crack formation is easier for QDs having short-chain ligands because of the weak interparticle attraction between QDs. Our findings reveal previously unknown defects of the intaglio printing process and provide guidance for mitigating these problems for preparing high-resolution QD patterns.