Direct Photolithographic Patterning of Colloidal Quantum Dots Enabled by UV-Crosslinkable and Hole-Transporting Polymer Ligands

Abstract

Quantum dot (QD)-based displays call for nondestructive, highthroughput, and high-resolution patterning techniques with micrometer precision. In particular, self-emissive QD-based displays demand fine patterns of conductive QD films with uniform thickness at the nanometer scale. To meet these requirements, we functionalized QDs with photopatternable and semiconducting poly(vinyltriphenylaminerandom-azidostyrene) (PTPA-N 3 -SH) ligands in which hole-transporting triphenylamine and UV-crosslinkable azide (−N 3 ) groups are integrated. The hybridized QD films undergo chemical crosslinking upon UV irradiation without loss in the luminescence efficiency, enabling micrometer-scale QD patterns (pitch size down to ∼10 μm) via direct photolithography. In addition, the conjugated moieties in the ligands allow the crosslinked QD films to be used in electrically driven light-emitting diodes (LED). As the ultimate achievement, a patterned QD-LED was prepared with a maximum luminance of 11 720 cd m −2 and a maximum external quantum efficiency (EQE) of 6.25%. The present study offers a simple platform to fabricate conductive nanoparticle films with micrometerscale patterns, and thus we anticipate that this system will expedite the realization of QD-based displays and will also be applicable to the manufacture of nanoparticles for other electronic devices.

Luminescence Enhancement, Encapsulation, and Patterning of Quantum Dots Toward Display Applications

“…Moreover, thiol-ene photopolymerization and vinyl polymerization have been proven to be versatile reactions to grow polymer networks. [86,91,94] The cross-linked polymer networks can help QDs disperse uniformly at high loading rates without noticeable aggregation. [92] By combining a solid-state polymer with imprinting lithography techniques, a micropatterned QDpolymer composite exhibiting superior photoluminescence properties can be fabricated.…”

“…[29,[91][92][93]135] In addition, photopatterned QDs can also be obtained by carefully screening the ligands, which will be discussed in Section 4.2. [94,107,136,137] [93] Copyright 2016, The Royal Society of Chemistry.…”

“…However, in the latter, QDs are located in predesigned positions and there are no QDs in the other area as the background, such as patterns formed by self-assembly, [138][139][140] stamping, [141] transfer printing, [142] inkjet printing, [143][144][145][146][147] and photolithography. [66,94,107,136,137,[148][149][150][151] Among these, photolithography and inkjet printing are potential techniques for large-scale fabrication in the display industry. A brief introduction is presented in the following sections, and the parameters used to compare different strategies are listed in Table 3.…”

64‐1: Invited Paper: Challenges for Realizing QD‐LED Display

“…It can also be an effective technique for QDs patterning, considering that the manufacturing equipment is already in place in display factories. Several photolithography like patterning process have been proposed: Ko et al 19 have used ultra violet rays (UV) to cure QD with cross-linkable ligand, Nakanishi et al 1 developed a UV curable resin containing QDs. Lift-off process is a variant of photolithography.…”

How Will Quantum Dots Enable Next‐Gen Display Technologies?

“…The photoresist pattern then is removed, leaving patterned QDs. For QD‐LED, both the lift‐off method 24 ‐ 26 and standard photolithography 27 , 28 method have been used. At Sharp Corporation, we have been developing a special photoresist and demonstrated a 6‐inch full‐color QD‐LED display 28 …”