Photopatterning Luminescent Quantum Dots
Electroluminescence from quantum dots (QDs) is a suitable photon source for futuristic displays offering hyper-realistic images with free-form factors. Accordingly, a nondestructive and scalable process capable of rendering multicolored QD patterns on a scale of several micrometers needs to be established. In this talk, two different nondestructive direct photopatterning methods for QDs are introduced, both of which exploit crosslinking reaction between the ligands of neighboring QDs. The first method exploits an additive that can crosslink with native aliphatic QD ligands. This additive is referred to as light-driven ligand crosslinker (LiXers) [1]. Specifically, we employ LiXers in branched structure containing multiple azide units [2]. The branched LiXers effectively interlock heavy-metal-free QD films via photocrosslinking native aliphatic QD surface ligands without compromising the intrinsic optoelectronic properties of QDs. Using branched LiXers with six sterically engineered azide units, we achieved RGB QD patterns on the micrometer scale. The photocrosslinking process did not affect the photoluminescence and electroluminescence characteristics of QDs and extended the device lifetime. Alternatively, QD ligands by themselves containing a photocrosslinkable moiety (that can also directly crosslink with native aliphatic ligands of neighboring QDs) can be anchored onto QD surface [3]. Specifically, photocrosslinkable ligands (PXLs) based on benzophenone derivative are exploited. The use of PXL permits employing a secondary ligand system (which is referred to as dispersing ligand, DL) that is devised to control the solubility of QDs to solvent. Based on a dual-ligand passivation system comprising PXL and DLs, we demonstrate that QDs can be direct patterned on various substrates using commercialized photolithography (i-line) or inkjet printing systems without compromising the optical properties of the QDs or the optoelectronic performance of the device. Our approaches offer versatile ways of creating various structures of luminescent QDs in a cost-effective and non-destructive manner. This could be implemented in nearly all commercial photonics applications where QDs are used.