Nondestructive Direct Photolithography for Patterning Quantum Dot Films by Atomic Layer Deposition of ZnO

Abstract

materials because of their high color purity, large-scale solution processability, and tunable electrical and optical properties. [1][2][3] The InP-based QDs have been synthesized with near-unity photoluminescence quantum yield (PL QY), which can meet the RoHS requirements by removing toxic Cd from QD emitters. [4,5] Despite recent advances in QD light-emitting diodes (QD-LEDs), including a 20% external quantum efficiency and enhanced device lifetime, [4,[6][7][8][9][10][11] multicolored and pixelated QD-LED devices still need to be developed. [12] The QDs are typically synthesized using wet chemistry, which is useful for large-scale solution processes. When QDs are incorporated into a device structure and sandwiched into a multilayered thin film, solvent orthogonality should be considered because the pre-coated QD layer can be damaged by the solvent in the top layers. This can be a serious issue when the QD film is patterned as a pixelated display, where conventional photolithography cannot be used. [13,14] When photoresists are coated on top of the pre-existing QD film, the QD film is easily removed, or the two layers intermix. This is because QDs are easily dissolved or washed with organic solvents, which are also used to dissolve the photoresist. Thus, alternative patterning methods, such as inkjet [15][16][17][18][19] and transfer printing, [20][21][22] have been employed to form multicolor QD patterns. However, inkjet printing has a limited tact time and suffers from nozzle clogging issues for industrial applications. [15,23] In addition, transfer printing can yield high-resolution patterns, but the process requires precise control of kinetic parameters, such as pick-up and peeling speed, which limits the reproducibility of the process. [21,22] Therefore, it is highly desirable to use conventional photolithography for patterning QD films. [24] Two methods have been suggested for employing photolithography to QD film patterning. One is the addition of light-sensitive cross-linking molecules to the QD solution. The molecule can either replace the original ligands or can be included as an additional substance. [25][26][27] Upon light exposure, the molecules form a crosslinked structure between the QDs, and the patterns can be formed by solvent dipping. The other method directly uses a conventional photoresist because it is a well-designed chemical that provides high resolution and etch-resistance. Owing to the absence of solvent resistance in QD films, the lift-off method Colloidal quantum dot-based light-emitting diodes (QD-LEDs) are one of the potential future self-emissive displays owing to their large-scale solutionprocessibility and high color purity. For the industrial application of QD-LEDs, high-performance QD-LED and high-resolution patterning of quantum dot (QD) films are required. Photolithography is an ideal tool for patterning QD films. Previously, the high-resolution patterning of QD films using direct photolithography by ultra-thin atomic layer deposition of ZnO on the QD surface is reported. Th...

High-Resolution Multicolor Patterning of InP Quantum Dot Films by Atomic Layer Deposition of ZnO

“…Typical aliphatic ligands, such as oleic acid and oleylamine, are not shown in the schematic, but the formation of ALD ZnO is adequately addressed. Similar to our previous studies, ,, the QD films subjected to ALD treatment exhibited improved device performance and significantly improved solvent resistance during the photolithography process. The QD solvent-dipping image in Figure a shows the different solvent resistances in the QD films with and without ALD ZnO treatment.…”

“…Depositing ultrathin ZnO on the QD surface or cross-linking the QD film surface is an effective approach to providing solvent resistance to the QD film . In our previous studies, photolithography-based high-resolution patterning of QD films was achieved by directly coating a photoresist (PR). , The Cd-based QD film was easily patterned by conventional PR coating, but the InP-based QD film was severely damaged during PR coating owing to the chemical weakness of the InP-based QD. Despite the solvent resistance of the QD film by the deposition of ultrathin ZnO films through atomic layer deposition (ALD), significant photoluminescence (PL) quenching was observed during the PR coating and subsequent photolithography process. , The negative-type PR successfully suppressed the PL quenching of the InP QD film by removing the sulfonic group; however, multicolor QD film patterning was not achieved owing to the hardening of the negative PR .…”

Facile Synthesis of Multicolored Stacked Quantum Dot Films for Efficient White Light Emission

“…Moreover, ALD enhances the performance of QD-LEDs, as shown in our previous studies. 33,34,36 In contrast to ZnO NPs that have surface defects and can cause PL quenching of QDs, 12 ALD of ZnO enhances the PL intensity of QDs. Figure S3 illustrates the PL spectra improvement of QD films for each primary color following the application of ultrathin ALD ZnO.…”

“…21,29 Atomic layer deposition (ALD) can be used to form an extremely thin passivation layer of ZnO on top of the QD film, such that even a single pulse of diethylzinc (DEZ) precursor can effectively cross-link the QDs on the film surface, as demonstrated in our previous studies. 33,34 In this study, a ZnO layer was inserted between two or more QD films via ALD to suppress the FRET effect and achieve white light emission for a wide range of operating voltages without significantly affecting the charge transport. In addition to this, stacking QDs with different emission colors by ALD ZnO efficiently controls the exciton recombination zone by changing the stacking sequence of R-, G-, and B-QD films.…”

Ultrahigh-resolution quantum dot patterning for advanced optoelectronic devices

“…While the device performances of InP QD-based QLEDs have reached industrial standards, PR used in the conventional patterning process reduces the PL intensity of InP QDs. 89 Therefore, challenges are proposed to adopt non-Cd based QDs in developed patterning technologies. These challenges include, but are not limited to, the development of photo-active ligands applicable to InP QD surfaces while preserving the PLQY of the QDs, and confirming the stability of InP QDs under widely used polar and nonpolar solvents.…”