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Review

Progress in the Development of Active-Matrix Quantum-Dot Light-Emitting Diodes Driven by Non-Si Thin-Film Transistors

by
Geun Woo Baek
1,
Yeon Jun Kim
1,
Minhyung Lee
1,
Yeunwoo Kwon
1,
Beomsoo Chun
1,
Ganghyun Park
1,
Hansol Seo
1,
Heesun Yang
2,* and
Jeonghun Kwak
1,*
1
Department of Electrical and Computer Engineering, Inter-University Semiconductor Research Center, Soft Foundry Institute, Seoul National University, Seoul 08826, Republic of Korea
2
Department of Materials Science and Engineering, Hongik University, Seoul 04066, Republic of Korea
*
Authors to whom correspondence should be addressed.
Materials 2022, 15(23), 8511; https://doi.org/10.3390/ma15238511
Submission received: 19 October 2022 / Revised: 18 November 2022 / Accepted: 27 November 2022 / Published: 29 November 2022
(This article belongs to the Special Issue Quantum Dots for Optoelectronic Devices)
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Versions Notes

Abstract

:
This paper aims to discuss the key accomplishments and further prospects of active-matrix (AM) quantum-dot (QD) light-emitting diodes (QLEDs) display. We present an overview and state-of-the-art of QLEDs as a frontplane and non-Si-based thin-film transistors (TFTs) as a backplane to meet the requirements for the next-generation displays, such as flexibility, transparency, low power consumption, fast response, high efficiency, and operational reliability. After a brief introduction, we first review the research on non-Si-based TFTs using metal oxides, transition metal dichalcogenides, and semiconducting carbon nanotubes as the driving unit of display devices. Next, QLED technologies are analyzed in terms of the device structure, device engineering, and QD patterning technique to realize high-performance, full-color AM-QLEDs. Lastly, recent research on the monolithic integration of TFT–QLED is examined, which proposes a new perspective on the integrated device. We anticipate that this review will help the readership understand the fundamentals, current state, and issues on TFTs and QLEDs for future AM-QLED displays.

1. Introduction

Colloidal quantum dots (QDs) have been regarded as promising emitters owing to their excellent optical properties, such as near-unity photoluminescence (PL) quantum yield (QY), narrow emission spectral bandwidth, and size-dependent bandgap tunability. Based on these merits, QDs can be utilized for a variety of applications, such as display devices, solar cells, and photodetectors [1,2,3,4,5,6,7,8,9,10]. In particular, QDs have been widely investigated for their use in display devices to improve the color gamut. For instance, a liquid crystal display (LCD), including a QD-based color conversion film, has already been commercialized. Meanwhile, interest in QD-based light-emitting diodes (QLEDs) has been increasing for decades to take advantage of their superb optoelectronic performance, solution-processability, and fabrication compatibility with existing technologies, which enabled QLEDs to exhibit high efficiency, luminance, and stability comparable with those of organic light-emitting diodes (OLEDs) [11,12,13,14,15,16]. Additionally, the demonstration of active-matrix (AM) QLED displays using a Si-based thin-film transistors (TFTs) backplane has been raising the expectation for high-quality displays [17,18,19,20,21,22]. Despite the remarkable development, however, further research on AM-QLEDs driven by non-Si-based TFTs is required to realize display devices with advanced features, e.g., transparency, flexibility, and stretchability, which has rarely been reported so far [23,24,25,26]. This may be because the TFT backplane needs to meet more stringent requirements, such as good electrical properties to drive high current, low response to light from QLED, and endurance to the solution-based QLED fabrication processes [27,28,29,30,31].
In this review, we aim to provide recent progress of non-Si-based TFTs and QLEDs for AM-QLED displays. In the first section, we briefly introduce the importance of using non-Si-based TFT backplane, the materials and technical issues of these TFTs using metal oxides, transition metal dichalcogenides (TMDCs), and semiconducting single-walled carbon nanotubes (SWNTs). Next, recent research on QLEDs as a frontplane device is reviewed in terms of device engineering, including the device architecture for QLEDs, device modification for performance improvements, and fine-patterning methods for QD films. Lastly, prospects and remaining challenges in research of TFT-driven AM-QLED displays will be discussed.

2. Non-Si TFT Backplane Technology

An AM backplane consists of at least two types of TFTs: a driving TFT to supply current to a subpixel and a switching TFT to turn on and off the addressed driving TFT. Therefore, the performance of backplane TFTs is important to properly provide signals and currents to subpixels. It is typically required for TFT devices to have good mobility for fast response, large on-current for high brightness, low leakage current for low power consumption, and high reliability for stable operation. For the AM-LCDs, amorphous Si is mostly used because it does not require high mobility to switch the subpixels. In the case of AM-OLED-based products, including mobile phones and televisions, low-temperature poly-Si (LTPS) is used to quickly drive a subpixel with sufficient current. However, these Si-based TFTs cannot be used for flexible and transparent displays. Thus, presently, n-type oxide TFTs, for example, indium gallium zinc oxide (IGZO), exhibiting high electron mobility (µe) of >10 cm2 V−1 s−1 and decent operational stability, are adopted for large-area and foldable AM-OLED displays. Various n-type oxide TFTs have also been utilized for AM-QLEDs [20,21,24,32], as shown in Figure 1. Nevertheless, p-type TFTs are also needed to comply with various QLED architectures (e.g., normal and inverted structures) and solution-based QLED fabrication processes. In this regard, TMDCs and semiconducting SWNTs exhibiting high hole mobility (µh) can be good candidates for p-type channel materials. In this section, we explain a fundamental circuit design for the AM driving mode, state-of-the-art, and remaining challenges of non-Si-based TFT backplane technologies for AM-QLEDs.

2.1. Circuits for AM Driving

As is well-known, a passive-matrix-driven display requires a regular scanning signal with a high frequency to make a subpixel be perceived as a turn-on state, which consumes a large amount of power. On the contrary, with the AM driving circuit that basically consists of two TFTs and one storage capacitor (CS) for a single pixel (i.e., the 2T1C structure), the light-emitting diode (LED) can continuously emit light even when the switching TFT has no signal, as shown in Figure 2a because CS can store the on/off state by holding the gate voltage of the driving TFT. Thus, it is essential to use the AM driving circuit for low power consumption and faster switching in the latest display devices.
In spite of these advantages, the AM driving method has a critical issue of non-uniform degradation of LEDs and TFTs in each pixel. In detail, LEDs may have different lifetimes for each individual color of subpixels. Similarly, TFTs suffer from uneven threshold voltage (VT) shifts originating from bias–temperature stress (BTS). In order to alleviate these phenomena, various compensation circuits have been proposed, including voltage (or current) programmable circuits and hybrid-type programmed circuits [33,34,35,36]. However, compensation circuits generally require more TFTs and capacitors, as exemplified in Figure 2b, which makes the TFT design and process steps complicated and increases the manufacturing cost of TFT backplanes. Therefore, TFTs with long-term reliability, high uniformity, and high performance needs to be developed continuously.

2.2. Active Materials for Non-Si TFT Backplane

In order to satisfy the aforementioned conditions, promising candidates have been researched, including metal oxides, TMDCs, and semiconducting SWNTs. Among these, oxide TFTs exhibit higher mobility than amorphous Si TFTs and improved uniformity in large-sized arrays than LTPS TFTs. Owing to these merits, oxide TFT-based AM-OLED displays have been successfully commercialized. However, the electron mobility of oxide TFTs needs to be improved further for a high scanning rate and high brightness by driving QLEDs with high currents. So far, researchers have reported several methods to increase the electrical properties of the oxide-based channel via tuning the chemical composition [37], post-treatment [38], a multilayered channel [39], a dual gate structure [40], and a high-k dielectric [41,42]. Based upon these efforts, Magari et al. recently reported a hydrogenated polycrystalline In2O3 TFT exhibiting a high µe of 139.2 cm2 V−1 s−1 by controlling the grain size and reducing defect sites [43].
However, oxide TFTs hardly operate in p-type. The integration of an n-type TFT and a normal structured QLED can cause an intricate fabrication procedure for wiring the drain electrode of the TFT with the top cathode of the QLED for electron injection. It may also increase the resistance causing Joule heating, which thus can reduce the response speed and degrade the reliability of the TFT backplane. Therefore, the development of p-type TFTs is necessary for high-performance AM-QLEDs. Previously, oxides were also one of the p-type channel candidates. However, p-type oxides, such as NiO, SnO, and CuO, mostly suffer from the lack of stability and possess an anisotropic, localized O 2p orbital with a large hole effective mass, leading to µh of <1 cm2 V−1 s−1 [44,45,46,47].
As an alternative, TMDCs in a chemical composition of MX2, where M is a transition metal (Mo, W, etc.) and X is a chalcogen (S, Se, or Te), have been focused as a promising p-channel material owing to their advanced properties, such as tunable bandgap depending on the number of layers, absence of dangling bonds, and resultingly a high on–off ratio with decent mobility. In addition, it is possible to form a functional heterostructure of two different materials. Among various TMDCs, MoTe2 can be a good choice for a TFT backplane because of its a few distinctive characteristics, i.e., insensitivity to light, easy type-convertibility, and bias stress instability [23,25,48]. On the other hand, exfoliation-based deposition and fine-patterning of the TMDC monolayer are the major obstacles to their application in large-area AM displays. Although technologies for high-resolution and large-scale fabrication have consistently progressed [49,50,51], they need to be developed more to satisfy customer expectations for large-sized displays.
For the large-area processability, semiconducting SWNTs would be an option for the TFT channel. The SWNT-based TFTs are easily fabricated using various solution processes at low temperatures, and they also show high device performance with intrinsic field-effect mobility (µh of up to ~102 cm2 V−1 s−1), flexibility, and transparency [52,53,54,55]. They are also resistant to the subsequent processes for patterning and QLED deposition. Contrary to the advantages, there are a few known issues of SWNTs, such as low chirality and poor dispersity in solution—though the chirality is improving gradually, reaching 99.999% or even higher purity through post-treatment [56,57,58], and the dispersity has been enhanced by wrapping with DNA or conjugated polymers [59,60,61,62]. Poor n-type performance of SWNTs also needs to be enhanced for practical use in a display backplane, to be combined with an inverted QLED. A few of the TFT performances using oxides, TMDCs, and SWNTs reported within five years are summarized in Table 1.
Organic semiconductors have also been considered as active channel materials. Several small molecules (e.g., pentacene, thienothiophene derivatives) and polymers have been studied owing to their low cost and facile fabrication with high scalability [63,64,65]. However, it has limitations to employ as backplane TFTs due to its low mobility, high threshold voltage, low BTS, and patterning issues [66,67]. These problems need to be overcome for their practical use in backplanes.
Table
Table 1. Summary of TFT parameters using oxides, TMDCs, and SWNTs.
Table 1. Summary of TFT parameters using oxides, TMDCs, and SWNTs.
YearChannel
Material		TypeMobility
(cm2 V−1 s−1)		Subthreshold Swing
(V dec−1)		Ion/off RatioThreshold Voltage
(V)		Reference
2018IGZOn61.30.08~1060.78[68]
MoS2n260-~106-[69]
SWNTn10-~108-[70]
2019IGZOn740.21~108−1.3[41]
MoS2n170-~106-[71]
SWNTp20.90.2~1040.4[72]
2020ZnONn1470.21~104−0.72[40]
MoS2n107-~106-[73]
SWNTp16---[74]
MoTe2p178.7-~107−22[75]
2021IGTO *n116.50.13~1090.47[76]
MoS2n44.60.36~105-[77]
SWNTp10.920.4~1050.48[78]
MoTe2p12.60.26~1040.87[79]
2022In2O3:Hn139.20.19-0.2[43]
MoS2n12.3-~109-[80]
SWNTp496-~108-[81]
MoTe2p30-~106−20[82]
* Indium-Gallium-Tin-Oxide.

3. QLED Frontplane Technology

A QLED is a device for utilizing electroluminescence (EL) from QDs, consisting of hole injection/transport layers (HIL/HTL), electron injection/transport layers (EIL/ETL), and a QD emissive layer between them, similar to an OLED structure. Since the first QLED was reported [83], the efficiency and operational lifetime have been improved owing to the advances in QD synthesis, surface treatment, device architecture, and fundamental understandings of the QLEDs [84]. To realize the AM-QLED display, QLEDs should have high efficiency and brightness for low power consumption and a long operational lifetime for maintaining image quality. High-resolution patterning of the QD layer is also required for future display devices. Improvement of electron–hole balance in a QLED is the most significant issue to be solved because it is directly related to several kinds of non-radiative recombination processes (e.g., Auger recombination and exciton–polaron quenching) which affect the QLED efficiency and efficiency roll-off. Despite multilateral efforts, it is not easy to fundamentally overcome this issue due to a few inherent characteristics of QDs and QLEDs—an extremely narrow exciton recombination zone [85] and large energy level offsets with poor interfacial morphology at the QD–organic interface. According to the device structure and process compatibility, the integration of a QLED with a driving TFT needs to be studied. In this section, we briefly review the progress of QLEDs toward high-performance AM-QLEDs from the viewpoints of the device structure and engineering of the QDs and charge transport layers for improved electron–hole balance.

3.1. Device Architecture for QLEDs

The device architecture of QLEDs can be classified in a number of ways. According to the stacking order of each functional layer, QLEDs can be distinguished into two types, a normal structure (also called a conventional or standard structure) and an inverted structure. Figure 3a shows a normal QLED structure with a schematic energy band diagram, which is composed in a sequence of the anode, HIL, HTL, QDs, ETL, EIL, and cathode from the substrate. Because solution-based QD deposition is likely to damage the underlying organic HIL/HTL layers, the selectivity of charge-transporting materials and fabrication steps are significantly influenced in this structure. Also, an HTL possessing a deep, highest-occupied-molecular-orbital (HOMO) energy level is favorable for hole injection from organic HTL to inorganic QDs due to a large energy barrier between them. On the contrary, an inverted QLED is produced in the opposite order, from the cathode at the bottom to the anode on the top, as depicted in Figure 3b. As reported previously [86], this structure is beneficial for electron injection from the bottom cathode to QDs by adopting metal oxide nanoparticles (e.g., ZnO, ZnMgO, SnO, etc.) as the ETL with resistance to the follow-up QD deposition process. They have a good µe of approximately 10−4–10−3 cm2 V−1 s−1 and well-alignment of the conduction band level with QDs [86]. The relatively high charge density of metal oxides can transfer electrons to negatively charge QDs even without bias, facilitating electron injection into QDs by Auger-assisted carrier injection [87,88]. It also allows the expanded choice of HTL materials with the desired energy levels and mobility for boosting the hole injection using various deposition methods. Lastly, the stacking order has an influence on QLED–TFT integration. Considering that QLED fabrication starts on a substrate with a TFT array, it is more propitious to combine a normal QLED with a p-type TFT to supply hole current to the bottom anode or, similarly, an inverted QLED with an n-type TFT.
Depending on the direction of light emission, QLEDs are divided into bottom- and top-emission structures, which should be taken into consideration when designing the AM-QLEDs. In the case of the bottom-emission structure, the AM-QLED backplane must be transparent because the light emitted from the QLED subpixel needs to travel through the substrate. But as opaque metal wiring and TFTs below QLEDs reduce the aperture ratio, the bottom-emission structure is limitedly used for large-area displays. On the other hand, the top-emission structure, consisting of a completely reflective bottom electrode and a (semi-)transparent top electrode, emits light in the opposite direction of the substrate. Thus, it guarantees light emission from the full-subpixel area without any impediments, leading to being commonly applied for small-sized displays. No substrate in the optical path may considerably improve the light outcoupling efficiency [89,90,91]. Also, a microcavity effect between two metallic electrodes can be utilized to tune the peak wavelength and enhance the color purity [92,93,94,95]. However, intense light emission in the normal direction results in a distorted angular profile of the Lambertian distribution, which may cause a poor viewing angle in display devices. Recently, a highly efficient top-emitting QLED with an angular-independent emission profile was demonstrated by introducing a nanosphere scattering layer [96]. Also, a high external quantum efficiency (EQE) of 32.5% was achieved by enhancing the light extraction efficiency owing to the reduced absorption and waveguide losses and minimizing the surface plasmon polariton mode at the metal–dielectric interface. More studies on top-emitting QLEDs are needed, considering the significance of this topic to the industry.
A tandem structure, composed of two or more EL units connected in series, is also applicable to QLEDs. Since a QLED is driven by current, an electrical series connection of them enables the operation of all the EL stacks at the same current level. Thus, the EQE and current efficiency tend to increase roughly in proportion to the number of EL units, but the driving voltage increases so that the power efficiency remains the same or slightly lower due to increased internal resistance [97,98,99,100]. Between each EL unit, a charge generation layer (CGL) or an interconnecting layer should be formed, in which electrons and holes are generated and supplied to adjacent two units, respectively. For that, the CGL generally comprises a planar heterojunction (e.g., p–n junction or p–metal junction) for efficient charge separation with properties of low resistance and high transparency. Particularly in QLEDs, the CGL deposition process needs to be compatible with the fabrication process of each EL unit, which makes it hard to stack multiple QLED units.

3.2. High-Performance QLEDs Based on Device Engineering

Within a certain QLED structure, we can further modify the properties of each constituting layer to improve device performance. In particular, poor charge balance is one critical issue in this research field, which can be resolved mainly by device engineering. For this, various approaches and methods have been suggested, such as doping or blending a charge transporting layer (CTL) or insertion of an additional layer, and QD surface treatment. First, changing the properties of the CTL by doping or mixing an additional material is an intuitive method. As mentioned above, there have been difficulties in hole injection into QDs, leading to a large number of researches on HTL modification. Doping the HTL with an electron acceptor, e.g., 2,3,5,6-tetrafluoro-7,7,8,8-tetracyanoquinodimethane (F4-TCNQ) and MoOx, improves hole conduction ability and further enhances the thermal stability of the HTL [101,102]. A composite HTL serves complementary properties of two materials in terms of energy level, mobility, and morphology, as shown in Figure 4a. In detail, small molecule–polymer composites typically exhibit good mobility from a small molecule in a robust polymer matrix. Representative small molecules for this purpose are 4,4′-bis(N-(3-methylphenyl)-N-phenylamino)biphenyl (TPD), 4,4′,4-tris(carbazol-9-yl)triphenylamine (TCTA) and 4,4′,N,N′-diphenylcarbazole (CBP), and widely-used matrix polymers are poly[N,N′-bis(4-butylphenyl)-N,N′-bis(phenyl)-benzidine] (poly-TPD), poly(9,9-dioctylfluorene-alt-N-(4-sec-butylphenyl)-diphenylamine) (TFB), and poly-N-vinylcarbazole (PVK) [103,104,105,106,107,108,109,110,111].
The properties of the ETL can also be modified by doping and additives. For instance, ZnO has good electrical properties for QLEDs but has defect states from intrinsic oxygen vacancy, resulting in device instability and severe exciton quenching. Metal-doped/alloyed ZnO, such as ZnMgO and Li/Al/Ga-doped ZnO, has been reported to show improved device performance of QLEDs [112,113,114,115]. Inserting an additional layer has also been demonstrated for high-performance QLEDs. Especially, the insertion of a poly(methylmethacrylate) (PMMA) layer near the QD layer effectively blocks leakage current through the QD layer to obtain high EQE [116,117]. Similar effects were reported by incorporating a thin insulating layer (e.g., Al2O3, polyethylenimine ethoxylated) and a thin semiconducting organic layer having low mobility and wide bandgap [118,119,120,121].
Materials 15 08511 g004 550
Figure 4. Device engineering methods: (a) Composite of PVK and TPD as the HTL for the QLED (Reproduced from [105] with permission from American Chemical Society). (b) Energy band diagram of the green QLED with interface-modified QDs (Reproduced from [122] with permission from Wiley). (c) Schematic illustration of an inverted top-emission QLED fabricated on substrates with a different heat dissipation property (Reproduced from [123] with permission from Wiley).
Figure 4. Device engineering methods: (a) Composite of PVK and TPD as the HTL for the QLED (Reproduced from [105] with permission from American Chemical Society). (b) Energy band diagram of the green QLED with interface-modified QDs (Reproduced from [122] with permission from Wiley). (c) Schematic illustration of an inverted top-emission QLED fabricated on substrates with a different heat dissipation property (Reproduced from [123] with permission from Wiley).
Materials 15 08511 g004
Modification of the QD surface with proper ligands is also an important strategy for achieving high performance because insulating surfactants surrounding the QDs can hinder charge transport. A few methods have been reported to improve the optoelectronic properties by QD surface modification, such as ligand exchange with shorter ligands, electron donating/accepting ligands, and semiconducting ligands. Ligands with shorter alkyl chains or smaller molecules instead of oleic acids may provide dense, uniform, and stable packing of QDs, resulting in enhanced carrier injection/transport in QLEDs [122,124,125,126,127]. Adopting the ligand with a strong dipole moment originating from the electron donor/acceptor group can shift the energy level of QDs, which is helpful for balancing charge injection into QDs. For example, 2-ethylhexane-1-thiol ligands upshifted the energy level of Zn1-xCdxSe/ZnSe/ZnS QDs and reduced the hole injection barrier, resulting in a current efficiency of 72 cd A−1, the maximum luminance of 334,000 cd m−2, and a half-lifetime of 140 h at an initial luminance (L0) of 17,200 cd m−2 which corresponds to that of 1,800,000 h at L0 of 100 cd m−2 by estimation [8].
Also, precise tuning of the energy level of QDs was demonstrated by ligand exchange with the series of thiophenol derivatives having a negative dipole moment, as shown in Figure 4b [122]. As a result, a green QLED exhibited improved current efficiency and maximum luminance of 98.2 cd A−1 and 106,400 cd m−2, respectively. Furthermore, QD surface treatment with halide anions can be a promising approach to enhance the QLED performance [14,113,125]. Ligand exchange and treatment with halides have effects in improving charge transport properties and reducing defects of QDs. Instead of insulating ligands, semiconducting ligands, which have a good charge transport property, have also been of interest for charge balance in QLEDs [126,127]. For the semiconducting property, the ligands typically contain bulkier functional groups in the form of oligomers or polymers. Thus, the QD film shows increased dot-to-dot distance but improved charge transport ability. Furthermore, it leads to the widening of the exciton recombination zone in the thicker emitting layer, which is ideal for reducing the efficiency roll-off.
Upon engineering the internal device structure, the introduction of a new substrate having a high thermal conductivity has recently been of interest in reducing thermal degradation. Joule heating is unavoidable in current-driven QLEDs, which deteriorates the efficiency and stability of the devices. Low thermal conductivity of the widely-used glass substrate (~1.0 W m−1 K−1) hinders heat dissipation and thereby increases the temperature of subpixels, which is known to accelerate irreversible thermal degradation of organic HTLs and QD ligands. To resolve this issue, Sun et al. employed a sapphire substrate with high thermal conductivity of 46 W m–1 K–1 and a thermally stable ligand, 1-dodecanethiol [12]. As a result, a high current efficiency of 75.3 cd A−1 and maximum luminance of 1,680,000 cd m−2 have been achieved in a green QLED. Recently, Lee et al. also demonstrated highly bright and stable QLED using a Si/SiO2 substrate with high thermal conductivity of ~150 W m–1 K–1 [123], as shown in Figure 4c. Based on additional device optimization, the QLED on the Si-based substrate exhibited a current efficiency and maximum luminance of 75.6 cd A−1 and 3,300,000 cd m−2, respectively.

3.3. QD Patterning Technologies

In order to realize AM-QLEDs, the QD layer should be formed in each individual subpixel. For this, QD patterning technologies have been investigated to comply with the requirements depending on the types of display application in terms of size, resolution, and the number of colors. In this section, we briefly introduce a few methodologies for QD patterning, such as contact printing, inkjet printing, photolithography, and light-induced direct QD patterning, and their pros and cons.
First, contact printing or contact transfer printing is one of the simplest patterning methods using an elastic stamp. A QD film deposited on a pre-patterned stamp can be transferred onto a target surface by using the difference of adhesion. In 2008, Kim et al. first reported a contact-printed QLED with a resolution of 1000 pixels-per-inch (PPI) using a Parylene-C-coated poly(dimethylsiloxane) (PDMS) stamp to control the surface energy and to prevent it from swirling by the QD solvent [128]. In 2011, Kim et al. introduced a self-assembled monolayer on the master substrate for easier detachment of the QD film and demonstrated a full-color AM-QLED [18]. Contact printing requires a high pressure to assure the transfer of QDs, and thus it is likely to damage the underlying layers and the transferred QD layer as well. In 2015, Cho et al. developed a soft contact QD transplanting technique, enabling the transfer of a QD layer onto a soft organic layer without pressure [129], as shown in the Figure 5a. Nevertheless, contact printing with a stamp is not desired in the industry because of several issues in printing accuracy, stamp reliability, limited printable area, and non-uniformity.
As a promising patterning technology, particularly for full-color AM-QLED displays, inkjet printing is attracting great attention from both academia and industry, owing to its high accuracy and low material usage based on drop-on-demand, and high throughput for large-area printing. On the other hand, poor film morphology is a weakness of inkjet printing. Inkjet-printed film morphology is related to several factors, such as the boiling point and vapor pressure of the solvent, the viscosity of ink, the surface energy of the substrate, and drying conditions. In most early-stage inkjet-printed QLEDs [132,133,134], the efficiency and brightness were relatively lower than those of the spin-coated QLED devices, mainly attributed to the poor QD morphology. Several strategies have been introduced to overcome this issue, such as using co-solvents to tune the boiling point and vapor pressure, mixing additives to control the viscosity, and substrate surface treatment to enhance wettability [130,135,136,137,138,139,140]. The Marangoni and capillary forces in a droplet can be optimized using these techniques to obtain a high-quality film. For example, Roh et al. reported QD–PMMA composite inks in a co-solvent to control the aforementioned key parameters and inkjet printing of fine QD films [130], as shown in Figure 5b. A ternary ink system consisting of octane, 1-cyclohexyl-ethanol, and n-butyl acetate was adopted to improve the morphology of QD film [15]. Recent intensive research on inkjet-printed QLEDs combined with device engineering has brought the inkjet-printed QLED performance to a level comparable to spin-coated ones [108,130,140,141], which should ease the commercialization of QLED displays.
Traditional photolithography can also be applied to pattern each QD subpixel. This matured technology provides a few advantages, such as high-resolution patterning and compatibility with the backplane fabrication procedure. However, there are several problems, for instance, physical damage to underlying QD and organic layers during photoresist (PR) deposition, development and removal processes, degradation of QDs by UV exposure, and defect formation from PR residues. Although full-color, high-resolution QLEDs could be demonstrated based on photolithography, the procedure to minimize the damages is exceedingly complicated [142,143]. Recently, a direct QD patterning method has been reported, which is a technique for patterning QDs based on photolithography but without the PR processes [131,144,145,146,147,148]. It can be achieved by adopting light-responsive ligands onto the surface of QDs, which chemically binds QDs upon illumination to firmly hold the pattern against the following wash-out step.
Specifically, in 2020, Cho et al. introduced direct optical lithography based QLEDs by employing photosensitive surface ligands, showing selective, full-color QD patterning with a small feature size of ~1.5 µm [146]. Yang et al. also reported a QD direct patterning method using a light-driven ligand crosslinker [131]. UV exposure to the modified QD film induces a chemical reaction between azides and the alkyl chain of QD ligands, resulting in a crosslinked QD layer, as shown in Figure 5c. Full-color, high-resolution QD patterns of >1400 PPI were demonstrated, and red crosslinked QLEDs exhibited an EQE of 14.6%. In 2022, Hahm et al. proposed direct patterning with dual ligands composed of dispersing ligands and photo-cross-linkable ligands to maintain the PL QY during photo-crosslinking [148]. As a result, they successfully demonstrated full-color QLED arrays employing the patterned QD films in a high resolution of >15000 PPI without a performance loss. Nevertheless, both traditional and direct photolithography requires a conventional UV lithography system for alignment and UV exposure, and thereby the processible substrates that can be processed are limited in size to the current wafer scale (300 mm). Thus, it is expected to be narrowly utilized for small-sized, high-resolution display devices, such as augmented/virtual reality (AR/VR) display devices.
Above and beyond these technologies, more QD patterning technologies, such as 3D printing [149,150], electrohydrodynamic printing [151], phase separation [152], electrophoretic deposition [153], and spatial light-assisted surface tailoring [154], have been introduced. However, these technologies are not suitable for implementing high-resolution displays and multilayer stacking or require complicated processes. Instead, we think that these technologies can be used in other ways, for instance, the fabrication of a QD color conversion layer for low-resolution displays or small lighting devices.

4. Monolithically Integrated TFT–QLED Devices

In Section 2 and Section 3, we reviewed the development of TFT and QLED devices, respectively, in terms of circuitry design and electrical requirements for reliable AM driving. However, monolithic integration of TFT–QLED requires the use of compatible processes to achieve high performance for both devices in a concise and effective TFT–QLED design with a tolerable fabrication procedure to each other. Thus, we think that it is important to investigate the fabrication process, optical and electrical properties, and any possible combinational issues in monolithically integrated TFT–QLED devices.
As reviewed above, an oxide TFT is one of the promising backplane devices, as already used in the industry. They also have large-area processability and high electrical performance sufficient to drive QLEDs. Recently, Chen et al. showed that the luminance of an inverted QLED could be competently controlled by an IGZO TFT [26]. In particular, they developed Al reaction-induced conductive a-IGZO as a common electrode, exhibiting a low sheet resistance (120 Ω sq–1) and a high transmittance (92.1%), demonstrating reduced photolithographic mask steps as well as higher power efficiency at the same time. In 2019, Li et al. showed QLED arrays integrated on inkjet-printed InGaO TFTs [24], which is suitable for large-area AM-QLED fabrication. To improve the quality of inkjet-printed oxides, they adopted a solvent printing method and demonstrated red-emitting QLED arrays driven by a 2T1C circuit, as shown in Figure 6a.
Owing to the remarkable development of TFTs using TMDCs as an active material, integration of the TMDC-based TFTs with QLEDs has been presented gradually. In 2019, Roh et al. reported an enhancement-mode n-type MoS2 TFT by octadecyltrichlorosilane (ODTS) SAM treatment to drive inverted QLEDs [23], as shown in Figure 6b. A deep-seated problem in depletion-mode TFTs is the large gate overdrive voltage ensuing rapid degradation of the channel. But the ODTS SAM enabled MoS2 TFTs to operate in an enhancement mode, leading to depopulate electrons on the back channel. As a result, they showed a wide-range operation of the QLEDs by controlling VT. In 2021, Baek et al. also demonstrated the stable operation of QLEDs driven by an integrated type convertible MoTe2 TFT [25], as shown in Figure 6c. In particular, they showed that the TFT–QLED integrated device exhibits a negligible response to visible light and a fast response time utilizing the properties of the MoTe2 channel. Also, a type-convertibility of the TFTs by simple poly-L-lysine (PLL) treatment was demonstrated, which allows using both normal and inverted structures of QLEDs.
As reviewed in this section, the research on TFT–QLED integrated devices is in its early stages but is gradually on the increase. The development of AM-QLED should be accompanied by not only respective performance improvement of the TFT backplane and QLED frontplane but also the requirements for monolithically integration in terms of circuitry design, the proper combination of TFT–QLED, and facile fabrication method. Such interest and intensive research would contribute to overcoming the known issues and limitations in regard to the fabrication process and reliability, enabling the realization of AM-QLEDs with advanced features.

5. Conclusions

In this review, we presented the fundamentals, state-of-the-art performance, and prospects of non-Si-based TFTs, QLEDs, and their combined forms, to achieve AM-QLED displays. As channel materials of the backplane TFT, metal oxides, TMDCs, and semiconducting SWNTs were considered to provide the requirements (e.g., high current driving, small VT shift under BTS) for future display devices. Their new features against Si, such as solution-processability, light-insensitivity, flexibility, and transparency, may lead to a strong chance of success in a display application, although there still exist several issues (e.g., performance, stability, and solution-based fine patterning) which need to be resolved. Examination of QLEDs from the viewpoint of device architecture, device engineering, and QD patterning is also meaningful, giving a new prospective on the future research direction. Although the QLEDs have been improved continuously, it is required to further develop more stable devices based on Cd-free QDs. In addition, the performance of pixelated QLEDs needs to be enhanced more. Finally, we reviewed the monolithic integration of TFT–QLED devices with the findings and issues toward AM-QLEDs. By solving the present issues, TFT-driven AM-QLEDs can be widely used as the main display panel with the advantages of a wide color gamut, high brightness, and low power consumption, which would expand the practical use from mobile devices and TVs to outdoor displays and AR/VR devices. We believe that this comprehensive review would be a valuable and inspiring guide for the readers in their future research with a wider perspective on AM-QLED displays.

Funding

This work was supported by the Creative-Pioneering Researchers Program through Seoul National University, by the Technology Innovation Program (20010737 and 20016332) funded by the Korean government (MOTIE), and by the National Research Foundation of Korea (NRF) grant (No. 2021R1A4A3032027) funded by the Korean government (MSIT).

Institutional Review Board Statement

Not applicable.

Informed Consent Statement

Not applicable.

Data Availability Statement

Not applicable.

Conflicts of Interest

The authors declare no conflict of interest.

References

  1. Aroutiounian, V.; Petrosyan, S.; Khachatryan, A.; Touryan, K. Quantum Dot Solar Cells. J. Appl. Phys. 2001, 89, 2268–2271. [Google Scholar] [CrossRef]
  2. Nozik, A.J. Quantum Dot Solar Cells. Phys. E Low-Dimens. Syst. Nanostruct. 2002, 14, 115–120. [Google Scholar] [CrossRef]
  3. Semonin, O.E.; Nozik, A.J.; Beard, M.C. In a Quantum Dot Solar Cell. Science 2013, 1530, 1530–1534. [Google Scholar]
  4. Shirasaki, Y.; Supran, G.J.; Bawendi, M.G.; Bulović, V. Emergence of Colloidal Quantum-Dot Light-Emitting Technologies. Nat. Photonics 2013, 7, 13–23. [Google Scholar] [CrossRef]
  5. Kim, M.R.; Ma, D. Quantum-Dot-Based Solar Cells: Recent Advances, Strategies, and Challenges. J. Phys. Chem. Lett. 2015, 6, 85–99. [Google Scholar] [CrossRef]
  6. Kim, T.H.; Lee, C.S.; Kim, S.; Hur, J.; Lee, S.; Shin, K.W.; Yoon, Y.Z.; Choi, M.K.; Yang, J.; Kim, D.H.; et al. Fully Stretchable Optoelectronic Sensors Based on Colloidal Quantum Dots for Sensing Photoplethysmographic Signals. ACS Nano 2017, 11, 5992–6003. [Google Scholar] [CrossRef] [PubMed]
  7. Kim, J.; Shim, H.J.; Yang, J.; Choi, M.K.; Kim, D.C.; Kim, J.; Hyeon, T.; Kim, D.H. Ultrathin Quantum Dot Display Integrated with Wearable Electronics. Adv. Mater. 2017, 29, 1700217. [Google Scholar] [CrossRef]
  8. Song, J.; Wang, O.; Shen, H.; Lin, Q.; Li, Z.; Wang, L.; Zhang, X.; Li, L.S. Over 30% External Quantum Efficiency Light-Emitting Diodes by Engineering Quantum Dot-Assisted Energy Level Match for Hole Transport Layer. Adv. Funct. Mater. 2019, 29, 1808377. [Google Scholar] [CrossRef]
  9. Livache, C.; Martinez, B.; Goubet, N.; Gréboval, C.; Qu, J.; Chu, A.; Royer, S.; Ithurria, S.; Silly, M.G.; Dubertret, B.; et al. A Colloidal Quantum Dot Infrared Photodetector and Its Use for Intraband Detection. Nat. Commun. 2019, 10, 2125. [Google Scholar] [CrossRef] [Green Version]
  10. Yin, X.; Zhang, C.; Guo, Y.; Yang, Y.; Xing, Y.; Que, W. PbS QD-based photodetectors: Future-oriented near-infrared detection technology. J. Mater. Chem. C 2021, 9, 417–438. [Google Scholar] [CrossRef]
  11. Li, Z.; Hu, Y.; Shen, H.; Lin, Q.; Wang, L.; Wang, H.; Zhao, W.; Li, L.S. Efficient and Long-Life Green Light-Emitting Diodes Comprising Tridentate Thiol Capped Quantum Dots. Laser Photonics Rev. 2017, 11, 1600227. [Google Scholar] [CrossRef]
  12. Sun, Y.; Su, Q.; Zhang, H.; Wang, F.; Zhang, S.; Chen, S. Investigation on Thermally Induced Efficiency Roll-Off: Toward Ef-ficient and Ultrabright Quantum-Dot Light-Emitting Diodes. ACS Nano 2019, 13, 11433–11442. [Google Scholar] [CrossRef] [PubMed]
  13. Li, Y.F.; Chou, S.Y.; Huang, P.; Xiao, C.; Liu, X.; Xie, Y.; Zhao, F.; Huang, Y.; Feng, J.; Zhong, H.; et al. Stretchable Organometal-Halide-Perovskite Quantum-Dot Light-Emitting Diodes. Adv. Mater. 2019, 31, 1807516. [Google Scholar] [CrossRef]
  14. Kim, T.; Kim, K.H.; Kim, S.; Choi, S.M.; Jang, H.; Seo, H.K.; Lee, H.; Chung, D.Y.; Jang, E. Efficient and stable blue quantum dot light-emitting diode. Nature 2020, 586, 385–389. [Google Scholar] [CrossRef]
  15. Jia, S.; Tang, H.; Ma, J.; Ding, S.; Qu, X.; Xu, B.; Wu, Z.; Li, G.; Liu, P.; Wang, K.; et al. High Performance Inkjet-Printed Quantum-Dot Light-Emitting Diodes with High Operational Stability. Adv. Opt. Mater. 2021, 9, 2101069. [Google Scholar] [CrossRef]
  16. Chao, W.C.; Chiang, T.H.; Liu, Y.C.; Huang, Z.X.; Liao, C.C.; Chu, C.H.; Wang, C.H.; Tseng, H.W.; Hung, W.Y.; Chou, P.T. High efficiency green InP quantum dot light-emitting diodes by balancing electron and hole mobility. Commun. Mater. 2021, 2, 96. [Google Scholar] [CrossRef]
  17. Cho, K.S.; Lee, E.K.; Joo, W.J.; Jang, E.; Kim, T.H.; Lee, S.J.; Kwon, S.J.; Han, J.Y.; Kim, B.K.; Choi, B.L.; et al. High-performance crosslinked colloidal quantum-dot light-emitting diodes. Nat. Photonics 2009, 3, 341–345. [Google Scholar] [CrossRef]
  18. Kim, T.H.; Cho, K.S.; Lee, E.K.; Lee, S.J.; Chae, J.; Kim, J.W.; Kim, D.H.; Kwon, J.Y.; Amaratunga, G.; Lee, S.Y.; et al. Full-colour quantum dot displays fabricated by transfer printing. Nat. Photonics 2011, 5, 176–182. [Google Scholar] [CrossRef]
  19. Yang, Y.; Zheng, Y.; Cao, W.; Titov, A.; Hyvonen, J.; Manders, J.R.; Xue, J.; Holloway, P.H.; Qian, L. High-efficiency light-emitting devices based on quantum dots with tailored nanostructures. Nat. Photonics 2015, 9, 259–265. [Google Scholar] [CrossRef]
  20. Lai, K.Y.; Yang, S.; Tsai, T.C.; Yao, I.A.; Yang, C.L.; Chang, C.C.; Chen, H.S. Top-Emitting Active-Matrix Quantum Dot Light-Emitting Diode Array with Optical Microcavity for Micro QLED Display. Nanomaterials 2022, 12, 2683. [Google Scholar] [CrossRef]
  21. Jiang, C.; Mu, L.; Zou, J.; He, Z.; Zhong, Z.; Wang, L.; Xu, M.; Wang, J.; Peng, J.; Cao, Y. Full-Color Quantum Dots Active Matrix Display Fabricated by Ink-Jet Printing. Sci. China Chem. 2017, 60, 1349–1355. [Google Scholar] [CrossRef]
  22. Li, Y.; Chen, Z.; Kristal, B.; Zhang, Y.; Li, D.; Yu, G.; Wang, X.; Wang, L.; Shi, Y.; Wang, Z.; et al. Developing AMQLED Technology for Display Applications. SID Int. Symp. Dig. Tech. Pap. 2018, 49, 1076–1079. [Google Scholar] [CrossRef]
  23. Roh, J.; Ryu, J.H.; Baek, G.W.; Jung, H.; Seo, S.G.; An, K.; Jeong, B.G.; Lee, D.C.; Hong, B.H.; Bae, W.K.; et al. Threshold Voltage Control of Multilayered MoS2 Field-Effect Transistors via Octadecyltrichlorosilane and Their Applications to Active Matrixed Quantum Dot Displays Driven by Enhancement-Mode Logic Gates. Small 2019, 15, 1803852. [Google Scholar] [CrossRef] [PubMed]
  24. Li, Y.; He, P.; Chen, S.; Lan, L.; Dai, X.; Peng, J. Inkjet-Printed Oxide Thin-Film Transistors Based on Nanopore-Free Aqueous-Processed Dielectric for Active-Matrix Quantum-Dot Light-Emitting Diode Displays. ACS Appl. Mater. Interfaces 2019, 11, 28052–28059. [Google Scholar] [CrossRef]
  25. Baek, G.W.; Seo, S.G.; Hahm, D.; Bae, W.K.; Kwak, J.; Jin, S.H. Highly Efficient, Surface Ligand Modified Quantum Dot Light-Emitting Diodes Driven by Type-Controllable MoTe2 Thin Film Transistors via Electron Charge Enhancer. Adv. Electron. Mater. 2021, 7, 2100535. [Google Scholar] [CrossRef]
  26. Chen, C.; Su, S.; Zhang, S.; Chen, S. Al Reaction-Induced Conductive a-InGaZnO as Pixel Electrode for Active-Matrix Quantum-Dot LED Displays. IEEE Electron Device Lett. 2022, 43, 749–752. [Google Scholar] [CrossRef]
  27. Jin, S.H.; Kang, S.K.; Cho, I.T.; Han, S.Y.; Chung, H.U.; Lee, D.J.; Shin, J.; Baek, G.W.; Kim, T.; Lee, J.H.; et al. Water-Soluble Thin Film Transistors and Circuits Based on Amorphous Indium-Gallium-Zinc Oxide. ACS Appl. Mater. Interfaces 2015, 7, 8268–8274. [Google Scholar] [CrossRef]
  28. Ryu, J.H.; Baek, G.W.; Yu, S.J.; Seo, S.G.; Jin, S.H. Photosensitive Full-Swing Multi-Layer MoS2 inverters with Light Shielding Layers. IEEE Electron Device Lett. 2017, 38, 67–70. [Google Scholar] [CrossRef]
  29. Choi, M.; Park, Y.J.; Sharma, B.K.; Bae, S.R.; Kim, S.Y.; Ahn, J.H. Flexible Active-Matrix Organic Light-Emitting Diode Display Enabled by MoS2 Thin-Film Transistor. Sci. Adv. 2018, 4, eaas8721. [Google Scholar] [CrossRef] [Green Version]
  30. Choi, M.; Bae, S.R.; Hu, L.; Hoang, A.T.; Kim, S.Y.; Ahn, J.H. Full-Color Active-Matrix Organic Light-Emitting Diode Display on Human Skin Based on a Large-Area MoS2 backplane. Sci. Adv. 2020, 6, eabb5898. [Google Scholar] [CrossRef]
  31. Khan, M.I.; Baek, G.W.; Kim, K.; Jin, S.H. Simultaneous Detection of Dopamine and Uric Acid on Indium Tin Oxides Modified with Cost-Effective Gas-Phase Synthesized Single Walled Carbon Nanotubes. Electroanalysis 2017, 29, 1925–1933. [Google Scholar] [CrossRef]
  32. Kim, J.; Lee, J.; Jang, J. AMQLED Display with Solution-Processed Oxide TFT Backplane. SID Int. Symp. Dig. Tech. Pap. 2018, 49, 1080–1083. [Google Scholar] [CrossRef]
  33. Srivastava, A.; Dubey, D.; Goswami, M.; Kandpal, K. Mechanical Strain and Bias-Stress Compensated, 6T-1C Pixel Circuit for Flexible AMOLED Displays. Microelectron. J. 2021, 117, 105266. [Google Scholar] [CrossRef]
  34. Wu, W.J.; Zhou, L.; Yao, R.H.; Peng, J.B. A New Voltage-Programmed Pixel Circuit for Enhancing the Uniformity of AMOLED Displays. IEEE Electron Device Lett. 2011, 32, 931–933. [Google Scholar] [CrossRef]
  35. Bang, J.S.; Kim, H.S.; Kim, K.D.; Kwon, O.J.; Shin, C.S.; Lee, J.; Cho, G.H. A Hybrid AMOLED Driver IC for Real-Time TFT Nonuniformity Compensation. IEEE J. Solid-State Circuits 2016, 51, 966–978. [Google Scholar]
  36. Lin, C.L.; Chang, W.Y.; Hung, C.C. Compensating Pixel Circuit Driving AMOLED Display with A-IGZO TFTs. IEEE Electron Device Lett. 2013, 34, 1166–1168. [Google Scholar] [CrossRef]
  37. Park, J.H.; Seok, H.J.; Kim, C.H.; Jung, S.H.; Cho, H.K.; Kim, H.K. Compositional Engineering of Hf-Doped InZnSnO Films for High-Performance and Stability Amorphous Oxide Semiconductor Thin Film Transistors. Adv. Electron. Mater. 2021, 7, 2001216. [Google Scholar] [CrossRef]
  38. Jeong, H.J.; Lee, H.M.; Ryu, C.H.; Park, E.J.; Han, K.L.; Hwang, H.J.; Ok, K.C.; Kim, H.S.; Park, J.S. Ultra-High-Speed Intense Pulsed-Light Irradiation Technique for High-Performance Zinc Oxynitride Thin-Film Transistors. ACS Appl. Mater. Interfaces 2019, 11, 4152–4158. [Google Scholar] [CrossRef]
  39. Chung, J.; Tak, Y.J.; Kim, W.G.; Park, J.W.; Kim, T.S.; Lim, J.H.; Kim, H.J. Low-Temperature Fabrication of Solution-Processed Hafnium Oxide Gate Insulator Films Using a Thermally Purified Solution Process. J. Mater. Chem. C 2018, 6, 4928–4935. [Google Scholar] [CrossRef]
  40. Park, E.J.; Lee, H.M.; Kim, Y.S.; Jeong, H.J.; Park, J.; Park, J.S. Transparent Flexible High Mobility TFTs Based on ZnON Semiconductor with Dual Gate Structure. IEEE Electron Device Lett. 2020, 41, 401–404. [Google Scholar] [CrossRef]
  41. Yang, J.; Zhang, Y.; Wu, Q.; Dussarrat, C.; Qi, J.; Zhu, W.; Ding, X.; Zhang, J. High-Performance 1-V ZnO Thin-Film Transistors with Ultrathin, ALD-Processed ZrO2 Gate Dielectric. IEEE Trans. Electron Devices 2019, 66, 3382–3386. [Google Scholar] [CrossRef]
  42. Ren, J.; Li, K.; Yang, J.; Lin, D.; Kang, H.; Shao, J.; Fu, R.; Zhang, Q. Solution-Processed Amorphous Gallium-Tin Oxide Thin Film for Low-Voltage, High-Performance Transistors. Sci. China Mater. 2019, 62, 803–812. [Google Scholar] [CrossRef]
  43. Magari, Y.; Kataoka, T.; Yeh, W.; Furuta, M. High-Mobility Hydrogenated Polycrystalline In2O3 (In2O3:H) Thin-Film Transistors. Nat. Commun. 2022, 13, 1078. [Google Scholar] [CrossRef] [PubMed]
  44. Li, Y.; Liu, C.; Wang, G.; Pei, Y. Investigation of Solution Combustion- Processed Nickel Oxide p-Channel Thin Film Transistors. Semicond. Sci. Technol. 2017, 32, 085004. [Google Scholar] [CrossRef]
  45. Liang, L.Y.; Liu, Z.M.; Cao, H.T.; Yu, Z.; Shi, Y.Y.; Chen, A.H.; Zhang, H.Z.; Fang, Y.Q.; Sun, X.L. Phase and Optical Characterizations of Annealed SnO Thin Films and Their P-Type TFT Application. J. Electrochem. Soc. 2010, 157, H598. [Google Scholar] [CrossRef]
  46. Sanal, K.C.; Vikas, L.S.; Jayaraj, M.K. Room Temperature Deposited Transparent P-Channel CuO Thin Film Transistors. Appl. Surf. Sci. 2014, 297, 153–157. [Google Scholar] [CrossRef]
  47. Ryu, J.H.; Baek, G.W.; Kim, S.Y.; Kwon, H.I.; Jin, S.H. Spray-Coated Single Walled Carbon Nanotubes as Source and Drain Electrodes in SnO Thin-Film Transistors. Semicond. Sci. Technol. 2018, 33, 075013. [Google Scholar] [CrossRef]
  48. Liu, N.; Baek, J.; Kim, S.M.; Hong, S.; Hong, Y.K.; Kim, Y.S.; Kim, H.S.; Kim, S.; Park, J. Improving the Stability of High-Performance Multilayer MoS2 Field-Effect Transistors. ACS Appl. Mater. Interfaces 2017, 9, 42943–42950. [Google Scholar] [CrossRef] [Green Version]
  49. Li, N.; Wang, Q.; Shen, C.; Wei, Z.; Yu, H.; Zhao, J.; Lu, X.; Wang, G.; He, C.; Xie, L.; et al. Large-Scale Flexible and Transparent Electronics Based on Monolayer Molybdenum Disulfide Field-Effect Transistors. Nat. Electron. 2020, 3, 711–717. [Google Scholar] [CrossRef]
  50. Zhu, K.; Wen, C.; Aljarb, A.A.; Xue, F.; Xu, X.; Tung, V.; Zhang, X.; Alshareef, H.N.; Lanza, M. The Development of Integrated Circuits Based on Two-Dimensional Materials. Nat. Electron. 2021, 4, 775–785. [Google Scholar] [CrossRef]
  51. Zhao, Y.; Song, Y.; Hu, Z.; Wang, W.; Chang, Z.; Zhang, Y.; Lu, Q.; Wu, H.; Liao, J.; Zou, W.; et al. Large-Area Transfer of Two-Dimensional Materials Free of Cracks, Contamination and Wrinkles via Controllable Conformal Contact. Nat. Commun. 2022, 13, 4409. [Google Scholar] [CrossRef] [PubMed]
  52. Tans, S.J.; Verschueren, A.R.M.; Dekker, C. Room-Temperature Transistor Based on a Single Carbon Nanotube. Nature 1998, 393, 49–52. [Google Scholar] [CrossRef]
  53. Artukovic, E.; Kaempgen, M.; Hecht, D.S.; Roth, S.; Grüner, G. Transparent and Flexible Carbon Nanotube Transistors. Nano Lett. 2005, 5, 757–760. [Google Scholar] [CrossRef] [PubMed] [Green Version]
  54. Sun, D.; Timmermans, M.Y.; Tian, Y.; Nasibulin, A.G.; Kauppinen, E.I.; Kishimoto, S.; Mizutani, T.; Ohno, Y. Flexible High-Performance Carbon Nanotube Integrated Circuits. Nat. Nanotechnol. 2011, 6, 156–161. [Google Scholar] [CrossRef] [PubMed]
  55. Sun, D.; Liu, C.; Ren, W.; Cheng, H. A Review of Carbon Nanotube- and Graphene-Based Flexible Thin-Film Transistors. Small 2013, 9, 1188–1205. [Google Scholar] [CrossRef] [PubMed]
  56. Liu, H.; Nishide, D.; Tanaka, T.; Kataura, H. Large-Scale Single-Chirality Separation of Single-Wall Carbon Nanotubes by Simple Gel Chromatography. Nat. Commun. 2011, 2, 309. [Google Scholar] [CrossRef] [Green Version]
  57. Tanaka, T.; Liu, H.; Fujii, S.; Kataura, H. From Metal/Semiconductor Separation to Single-chirality Separation of Single-wall Carbon Nanotubes Using Gel. Phys. Status Solidi-Rapid Res. Lett. 2011, 5, 301–306. [Google Scholar] [CrossRef]
  58. Rojas, W.A.G.; Hersam, M.C. Chirality-Enriched Carbon Nanotubes for Next-Generation Computing. Adv. Mater. 2020, 32, 1905654. [Google Scholar] [CrossRef]
  59. Tu, X.; Zheng, M. A DNA-Based Approach to the Carbon Nanotube Sorting Problem. Nano Res. 2008, 1, 185–194. [Google Scholar] [CrossRef] [Green Version]
  60. Asada, Y.; Miyata, Y.; Ohno, Y.; Kitaura, R.; Sugai, T.; Mizutani, T.; Shinohara, H. High-Performance Thin-Film Transistors with DNA-Assisted Solution Processing of Isolated Single-Walled Carbon Nanotubes. Adv. Mater. 2010, 22, 2698–2701. [Google Scholar] [CrossRef]
  61. Gomulya, W.; Gao, J.; Loi, M.A. Conjugated Polymer-Wrapped Carbon Nanotubes: Physical Properties and Device Applications. Eur. Phys. J. B 2013, 86, 404. [Google Scholar] [CrossRef]
  62. Samanta, S.K.; Fritsch, M.; Scherf, U.; Gomulya, W.; Bisri, S.Z.; Loi, M.A. Conjugated Polymer-Assisted Dispersion of Single-Wall Carbon Nanotubes: The Power of Polymer Wrapping. Acc. Chem. Res. 2014, 47, 2446–2456. [Google Scholar] [CrossRef] [PubMed]
  63. Chen, H.; Xing, X.; Zhu, M.; Cao, J.; Ali, M.U.; Li, A.; He, Y.; Meng, H. Low-Voltage, High-Performance Flexible Organic Field-Effect Transistors Based on Ultrathin Single-Crystal Microribbons. ACS Appl. Mater. Interfaces 2019, 11, 34188–34195. [Google Scholar] [CrossRef] [PubMed]
  64. Peng, B.; Ji, X.; Jiao, X.; Chu, M.; Liu, J.; Li, Y.; Chen, M.; Zhou, Z.; Zhang, C.; Miao, Q.; et al. A Transfer Method for High-Mobility, Bias-Stable, and Flexible Organic Field-Effect Transistors. Adv. Mater. Technol. 2020, 5, 2000169. [Google Scholar] [CrossRef]
  65. Han, M.J.; Lee, D.W.; Lee, E.K.; Kim, J.Y.; Jung, J.Y.; Kang, H.; Ahn, H.; Shin, T.J.; Yoon, D.K.; Park, J. Il Molecular Orientation Control of Liquid Crystal Organic Semiconductor for High-Performance Organic Field-Effect Transistors. ACS Appl. Mater. Interfaces 2021, 13, 11125–11133. [Google Scholar] [CrossRef]
  66. Haase, K.; Teixeira da Rocha, C.; Hauenstein, C.; Zheng, Y.; Hambsch, M.; Mannsfeld, S.C.B. High-Mobility, Solution-Processed Organic Field-Effect Transistors from C8-BTBT:Polystyrene Blends. Adv. Electron. Mater. 2018, 4, 1800076. [Google Scholar] [CrossRef]
  67. Fu, B.; Sun, L.; Liu, L.; Ji, D.; Zhang, X.; Yang, F.; Hu, W. Low-Power High-Mobility Organic Single-Crystal Field-Effect Transistor. Sci. China Mater. 2022, 65, 2779–2785. [Google Scholar] [CrossRef]
  68. Xia, G.; Zhang, Q.; Wang, S. High-Mobility IGZO TFTs by Infrared Radiation Activated Low-Temperature Solution Process. IEEE Electron Device Lett. 2018, 39, 1868–1871. [Google Scholar] [CrossRef]
  69. Liu, Y.; Guo, J.; Zhu, E.; Liao, L.; Lee, S.-J.; Ding, M.; Shakir, I.; Gambin, V.; Huang, Y.; Duan, X. Approaching the Schottky–Mott Limit in van Der Waals Metal–Semiconductor Junctions. Nature 2018, 557, 696–700. [Google Scholar] [CrossRef]
  70. Schneider, S.; Brohmann, M.; Lorenz, R.; Hofstetter, Y.J.; Rother, M.; Sauter, E.; Zharnikov, M.; Vaynzof, Y.; Himmel, H.-J.; Zaumseil, J. Efficient n-Doping and Hole Blocking in Single-Walled Carbon Nanotube Transistors with 1,2,4,5Tetrakis(Tetramethylguanidino)Ben-Zene. ACS Nano 2018, 12, 5895–5902. [Google Scholar] [CrossRef]
  71. Wang, Y.; Kim, J.C.; Wu, R.J.; Martinez, J.; Song, X.; Yang, J.; Zhao, F.; Mkhoyan, A.; Jeong, H.Y.; Chhowalla, M. Van Der Waals Contacts between Three-Dimensional Metals and Two-Dimensional Semiconductors. Nature 2019, 568, 70–74. [Google Scholar] [CrossRef] [PubMed]
  72. Zhang, Z.; Zhang, M.; Du, C.; Li, L.; Chang, K.-C. Improving Performance of All-Carbon-Nanotube Thin-Film Transistors by Low Temperature Supercritical CO2 Fluid Activation. IEEE Electron Device Lett. 2019, 40, 921–924. [Google Scholar] [CrossRef]
  73. Sanjay, S.; Sahoo, K.; Bhat, N. Alcohol-Based Sulfur Treatment for Improved Performance and Yield in Local Back-Gated and Channel-Length-Scaled MoS₂ FETs. IEEE Trans. Electron Devices 2020, 67, 3711–3715. [Google Scholar] [CrossRef]
  74. Salazar-Rios, J.M.; Sengrian, A.A.; Talsma, W.; Duim, H.; Abdu-Aguye, M.; Jung, S.; Fröhlich, N.; Allard, S.; Scherf, U.; Loi, M.A. Customizing the Polarity of Single-Walled Carbon-Nanotube Field-Effect Transistors Using Solution-Based Additives. Adv. Electron. Mater. 2020, 6, 1900789. [Google Scholar] [CrossRef] [Green Version]
  75. Iqbal, M.W.; Elahi, E.; Amin, A.; Aftab, S.; Aslam, I.; Hussain, G.; Shehzad, M.A. A Facile Route to Enhance the Mobility of MoTe2 Field Effect Transistor via Chemical Doping. Superlattices Microstruct. 2020, 147, 106698. [Google Scholar] [CrossRef]
  76. Kim, B.K.; On, N.; Choi, C.H.; Kim, M.J.; Kang, S.; Lim, J.H.; Jeong, J.K. Polycrystalline Indium Gallium Tin Oxide Thin-Film Transistors with High Mobility Exceeding 100 cm2/Vs. IEEE Electron Device Lett. 2021, 42, 347–350. [Google Scholar] [CrossRef]
  77. Kumar, S.; Sharma, A.; Tomar, M.; Gupta, V. Realization of Low-Power and High Mobility Thin Film Transistors Based on MoS2 Layers Grown by PLD Technique. Mater. Sci. Eng. B 2021, 266, 115047. [Google Scholar] [CrossRef]
  78. Kim, S.; Baek, G.W.; Jeong, J.; Seo, S.G.; Jin, S.H. Scalable and Selective N-Type Conversion for Carbon Nanotube Transistors via Patternable Polyvinyl Alcohol Stacked with Hydrophobic Layers and Their Application to Complementary Logic Circuits. J. Mater. Res. Technol. 2021, 12, 243–256. [Google Scholar] [CrossRef]
  79. Seo, S.G.; Jeong, J.; Kim, S.Y.; Kim, S.; Kim, K.; Kim, K.; Jin, S.H. Bias Stress Instability in Multilayered MoTe2 Field Effect Transistors under DC and Pulse-Mode Operation. Electron. Lett. 2021, 57, 193–195. [Google Scholar] [CrossRef]
  80. Hwangbo, S.; Hu, L.; Hoang, A.T.; Choi, J.Y.; Ahn, J.-H. Wafer-Scale Monolithic Integration of Full-Colour Micro-LED Display Using MoS2 Transistor. Nat. Nanotechnol. 2022, 17, 500–506. [Google Scholar] [CrossRef]
  81. Sun, Y.; Li, P.; Kauppinen, E.I.; Sun, D.-M.; Ohno, Y. Key Factors for Ultra-High on/off Ratio Thin-Film Transistors Using as-Grown Carbon Nanotube Networks. RSC Adv. 2022, 12, 16291–16295. [Google Scholar] [CrossRef] [PubMed]
  82. Huyen Nguyen, P.; Hieu Nguyen, D.; Kim, H.; Jeong, H.M.; Oh, H.M.; Jeong, M.S. Synergistic Hole-Doping on Ultrathin MoTe2 for Highly Stable Unipolar Field-Effect Transistor. Appl. Surf. Sci. 2022, 596, 153567. [Google Scholar] [CrossRef]
  83. Colvin, V.L.; Schlamp, M.C.; Alivisatos, A.P. Light-Emitting Diodes Made from Cadmium Selenide Nanocrystals and a Semiconducting Polymer. Nature 1994, 370, 354–357. [Google Scholar] [CrossRef]
  84. Jang, H.J.; Lee, J.Y.; Baek, G.W.; Kwak, J.; Park, J.-H. Progress in the development of the display performance of AR, VR, QLED and OLED devices in recent years. J. Inf. Disp. 2022, 23, 1–17. [Google Scholar] [CrossRef]
  85. Bae, W.K.; Kwak, J.; Lim, J.; Lee, D.; Nam, M.K.; Char, K.; Lee, C.; Lee, S. Multicolored light-emitting diodes based on all-quantum-dot multilayer films using layer-by-layer assembly method. Nano Lett. 2010, 10, 2368–2373. [Google Scholar] [CrossRef] [PubMed]
  86. Kwak, J.; Bae, W.K.; Lee, D.; Park, I.; Lim, J.; Park, M.; Cho, H.; Woo, H.; Yoon, D.Y.; Char, K.; et al. Bright and efficient full-color colloidal quantum dot light-emitting diodes using an inverted device structure. Nano Lett. 2012, 12, 2362–2366. [Google Scholar] [CrossRef]
  87. Qian, L.; Zheng, Y.; Choudhury, K.R.; Bera, D.; So, F.; Xue, J.; Holloway, P.H. Electroluminescence from Light-Emitting Polymer/ZnO Nanoparticle Heterojunctions at Sub-Bandgap Voltages. Nano Today 2010, 5, 384–389. [Google Scholar] [CrossRef]
  88. Qian, L.; Zheng, Y.; Xue, J.; Holloway, P.H. Stable and Efficient Quantum-Dot Light-Emitting Diodes Based on Solution-Processed Multilayer Structures. Nat. Photonics 2011, 5, 543–548. [Google Scholar] [CrossRef]
  89. Yang, X.; Mutlugun, E.; Dang, C.; Dev, K.; Gao, Y.; Tan, S.T.; Sun, X.W.; Demir, H.V. Highly flexible, electrically driven, top-emitting, quantum dot light-emitting stickers. ACS Nano 2014, 8, 8224–8231. [Google Scholar] [CrossRef]
  90. Ding, K.; Fang, Y.; Dong, S.; Chen, H.; Luo, B.; Jiang, K.; Gu, H.; Fan, L.; Liu, S.; Hu, B.; et al. 24.1% External Quantum Efficiency of Flexible Quantum Dot Light-Emitting Diodes by Light Extraction of Silver Nanowire Transparent Electrodes. Adv. Opt. Mater. 2018, 6, 1800347. [Google Scholar] [CrossRef]
  91. Li, D.; Feng, J.; Zhu, Y.; Lu, Z.; Pei, C.; Chen, Z.; Li, Y.; Li, X.; Xu, X. Enhanced efficiency of top-emission InP-based green quantum dot light-emitting diodes with optimized angular distribution. Nano Research 2021, 14, 4243–4249. [Google Scholar] [CrossRef]
  92. Chen, L.; Qin, Z.; Chen, S. Ultrahigh Resolution Pixelated Top-Emitting Quantum-Dot Light-Emitting Diodes Enabled by Color-Converting Cavities. Small Methods 2022, 6, 2101090. [Google Scholar] [CrossRef] [PubMed]
  93. Liu, G.; Zhou, X.; Chen, S. Very bright and efficient microcavity top-emitting quantum dot light-emitting diodes with Ag electrodes. ACS Appl. Mater. Interfaces 2016, 8, 16768–16775. [Google Scholar] [CrossRef] [PubMed]
  94. Zhang, X.; Pan, T.; Zhang, J.; Zhang, L.; Liu, S.; Xie, W. Color-tunable, spectra-stable flexible white top-emitting organic light-emitting devices based on alternating current driven and dual-microcavity technology. ACS Photonics 2019, 6, 2350–2357. [Google Scholar] [CrossRef]
  95. Yu, H.; Zhu, H.; Xu, M.; Zhang, J.; Feng, H.; Zhang, L.; Liu, S.; Xie, W. High-Efficiency, Large-Area, Flexible Top-Emitting Quantum-Dot Light-Emitting Diode. ACS Photonics 2022. [Google Scholar] [CrossRef]
  96. Shi, L.; Chen, S. Over 32.5% Efficient Top-Emitting Quantum-Dot LEDs with Angular-Independent Emission. ACS Appl. Mater. Interfaces 2022, 14, 30039–30045. [Google Scholar] [CrossRef]
  97. Kim, H.-M.; Lee, J.; Hwang, E.; Kim, J.; Jang, J. P-95: Inverted tandem architecture of quantum-dot light emitting diodes with solution processed charge generation layers. SID Int. Symp. Dig. Tech. Pap. 2016, 47, 1480–1483. [Google Scholar] [CrossRef]
  98. Zhang, H.; Sun, X.; Chen, S. Over 100 cd A− 1 efficient quantum dot light-emitting diodes with inverted tandem structure. Adv. Funct. Mater. 2017, 27, 1700610. [Google Scholar] [CrossRef]
  99. Zhang, H.; Chen, S.; Sun, X.W. Efficient red/green/blue tandem quantum-dot light-emitting diodes with external quantum efficiency exceeding 21%. ACS nano 2018, 12, 697–704. [Google Scholar] [CrossRef]
  100. Su, Q.; Zhang, H.; Chen, S. Flexible and tandem quantum-dot light-emitting diodes with individually addressable red/green/blue emission. npj Flex. Electron. 2021, 5, 8. [Google Scholar] [CrossRef]
  101. Cho, S.-Y.; Oh, N.; Nam, S.; Jiang, Y.; Shim, M. Enhanced device lifetime of double-heterojunction nanorod light-emitting diodes. Nanoscale 2017, 9, 6103–6110. [Google Scholar] [CrossRef] [PubMed]
  102. Yun, J.; Kim, J.; Jung, B.J.; Kim, G.; Kwak, J. Enhanced efficiency and high temperature stability of hybrid quantum dot light-emitting diodes using molybdenum oxide doped hole transport layer. RSC Adv. 2019, 9, 16252–16257. [Google Scholar] [CrossRef] [PubMed]
  103. Bae, W.K.; Kwak, J.; Lim, J.; Lee, D.; Nam, M.K.; Char, K.; Lee, C.; Lee, S. Deep blue light-emitting diodes based on Cd1− xZnxS@ ZnS quantum dots. Nanotechnology 2009, 20, 075202. [Google Scholar] [CrossRef] [PubMed]
  104. Li, Y.; Hou, X.; Dai, X.; Yao, Z.; Lv, L.; Jin, Y.; Peng, X. Stoichiometry-controlled InP-based quantum dots: Synthesis, photoluminescence, and electroluminescence. J. Am. Chem. Soc. 2019, 141, 6448–6452. [Google Scholar] [CrossRef]
  105. Li, J.; Liang, Z.; Su, Q.; Jin, H.; Wang, K.; Xu, G.; Xu, X. Small molecule-modified hole transport layer targeting low turn-on-voltage, bright, and efficient full-color quantum dot light emitting diodes. ACS Appl. Mater. Interfaces 2018, 10, 3865–3873. [Google Scholar] [CrossRef]
  106. Hong, A.; Kim, J.; Kwak, J. Sunlike White Quantum Dot Light-Emitting Diodes with High Color Rendition Quality. Adv. Opt. Mater. 2020, 8, 2001051. [Google Scholar] [CrossRef]
  107. Yang, P.; Zhang, L.; Kang, D.J.; Strahl, R.; Kraus, T. High-resolution inkjet printing of quantum dot light-emitting microdiode arrays. Adv. Opt. Mater. 2020, 8, 1901429. [Google Scholar] [CrossRef] [Green Version]
  108. Chen, M.; Xie, L.; Wei, C.; Yi, Y.-Q.-Q.; Chen, X.; Yang, J.; Zhuang, J.; Li, F.; Su, W.; Cui, Z. High performance inkjet-printed QLEDs with 18.3% EQE: Improving interfacial contact by novel halogen-free binary solvent system. Nano Res. 2021, 14, 4125–4131. [Google Scholar] [CrossRef]
  109. Han, M.G.; Lee, Y.; Kwon, H.-i.; Lee, H.; Kim, T.; Won, Y.-H.; Jang, E. InP-based quantum dot light-emitting diode with a blended emissive layer. ACS Energy Lett. 2021, 6, 1577–1585. [Google Scholar] [CrossRef]
  110. Zhang, Y.; Li, Z.; Wang, F.; Lin, Q.; Zhao, M. To improve the performance of green light-emitting devices by enhancing hole injection efficiency. Chem. Eng. J. Adv. 2021, 5, 100082. [Google Scholar] [CrossRef]
  111. Lee, S.; Hahm, D.; Yoon, S.-Y.; Yang, H.; Bae, W.K.; Kwak, J. Quantum-dot and organic hybrid light-emitting diodes employing a blue common layer for simple fabrication of full-color displays. Nano Res. 2022, 15, 6477–6482. [Google Scholar] [CrossRef]
  112. Li, X.; Zhao, Y.-B.; Fan, F.; Levina, L.; Liu, M.; Quintero-Bermudez, R.; Gong, X.; Quan, L.N.; Fan, J.; Yang, Z. Bright colloidal quantum dot light-emitting diodes enabled by efficient chlorination. Nat. Photonics 2018, 12, 159–164. [Google Scholar] [CrossRef]
  113. Won, Y.-H.; Cho, O.; Kim, T.; Chung, D.-Y.; Kim, T.; Chung, H.; Jang, H.; Lee, J.; Kim, D.; Jang, E. Highly efficient and stable InP/ZnSe/ZnS quantum dot light-emitting diodes. Nature 2019, 575, 634–638. [Google Scholar] [CrossRef] [PubMed]
  114. Alexandrov, A.; Zvaigzne, M.; Lypenko, D.; Nabiev, I.; Samokhvalov, P. Al-, Ga-, Mg-, or Li-doped zinc oxide nanoparticles as electron transport layers for quantum dot light-emitting diodes. Sci. Rep. 2020, 10, 7496. [Google Scholar] [CrossRef] [PubMed]
  115. Moon, H.; Lee, W.; Kim, J.; Lee, D.; Cha, S.; Shin, S.; Chae, H. Composition-tailored ZnMgO nanoparticles for electron transport layers of highly efficient and bright InP-based quantum dot light emitting diodes. Chem. Commun. 2019, 55, 13299–13302. [Google Scholar] [CrossRef]
  116. Dai, X.; Zhang, Z.; Jin, Y.; Niu, Y.; Cao, H.; Liang, X.; Chen, L.; Wang, J.; Peng, X. Solution-processed, high-performance light-emitting diodes based on quantum dots. Nature 2014, 515, 96–99. [Google Scholar] [CrossRef]
  117. Lin, Q.; Wang, L.; Li, Z.; Shen, H.; Guo, L.; Kuang, Y.; Wang, H.; Li, L.S. Nonblinking quantum-dot-based blue light-emitting diodes with high efficiency and a balanced charge-injection process. ACS Photonics 2018, 5, 939–946. [Google Scholar] [CrossRef]
  118. Kim, D.; Fu, Y.; Kim, S.; Lee, W.; Lee, K.H.; Chung, H.K.; Lee, H.J.; Yang, H.; Chae, H. Polyethylenimine ethoxylated-mediated all-solution-processed high-performance flexible inverted quantum dot-light-emitting device. ACS Nano 2017, 11, 1982–1990. [Google Scholar] [CrossRef]
  119. Lee, T.; Hahm, D.; Kim, K.; Bae, W.K.; Lee, C.; Kwak, J. Highly efficient and bright inverted top-emitting InP quantum dot light-emitting diodes introducing a hole-suppressing interlayer. Small 2019, 15, 1905162. [Google Scholar] [CrossRef]
  120. Li, D.; Bai, J.; Zhang, T.; Chang, C.; Jin, X.; Huang, Z.; Xu, B.; Li, Q. Blue quantum dot light-emitting diodes with high luminance by improving the charge transfer balance. Chem. Commun. 2019, 55, 3501–3504. [Google Scholar] [CrossRef]
  121. Rhee, S.; Chang, J.H.; Hahm, D.; Jeong, B.G.; Kim, J.; Lee, H.; Lim, J.; Hwang, E.; Kwak, J.; Bae, W.K. Tailoring the electronic landscape of quantum dot light-emitting diodes for high brightness and stable operation. ACS Nano 2020, 14, 17496–17504. [Google Scholar] [CrossRef] [PubMed]
  122. Moon, H.; Chae, H. Efficiency enhancement of all-solution-processed inverted-structure green quantum dot light-emitting diodes via partial ligand exchange with thiophenol derivatives having negative dipole moment. Adv. Opt. Mater. 2020, 8, 1901314. [Google Scholar] [CrossRef]
  123. Lee, T.; Kim, B.J.; Lee, H.; Hahm, D.; Bae, W.K.; Lim, J.; Kwak, J. Bright and Stable Quantum Dot Light-Emitting Diodes. Adv. Mater. 2022, 34, 2106276. [Google Scholar] [CrossRef] [PubMed]
  124. Rhee, S.; Hahm, D.; Seok, H.-J.; Chang, J.H.; Jung, D.; Park, M.; Hwang, E.; Lee, D.C.; Park, Y.-S.; Kim, H.-K. Steering Interface Dipoles for Bright and Efficient All-Inorganic Quantum Dot Based Light-Emitting Diodes. ACS Nano 2021, 15, 20332–20340. [Google Scholar] [CrossRef]
  125. Kang, B.-H.; Lee, J.-S.; Lee, S.-W.; Kim, S.-W.; Lee, J.-W.; Gopalan, S.-A.; Park, J.-S.; Kwon, D.-H.; Bae, J.-H.; Kim, H.-R. Efficient exciton generation in atomic passivated CdSe/ZnS quantum dots light-emitting devices. Sci. Rep. 2016, 6, 34659. [Google Scholar] [CrossRef] [Green Version]
  126. Bae, W.K.; Lim, J.; Zorn, M.; Kwak, J.; Park, Y.-S.; Lee, D.; Lee, S.; Char, K.; Zentel, R.; Lee, C. Reduced efficiency roll-off in light-emitting diodes enabled by quantum dot–conducting polymer nanohybrids. J. Mater. Chem. C 2014, 2, 4974–4979. [Google Scholar] [CrossRef]
  127. Park, Y.; Klöckner, B.; Hahm, D.; Kim, J.; Lee, T.; Kim, J.; Bae, W.K.; Zentel, R.; Kwak, J. Origin of enhanced efficiency and stability in diblock copolymer-grafted Cd-free quantum dot-based light-emitting diodes. J. Mater. Chem. C 2021, 9, 10398–10405. [Google Scholar] [CrossRef]
  128. Kim, L.A.; Anikeeva, P.O.; Coe-Sullivan, S.A.; Steckel, J.S.; Bawendi, M.G.; Bulović, V. Contact Printing of Quantum Dot Light-Emitting Devices. Nano Lett. 2008, 8, 4513–4517. [Google Scholar] [CrossRef]
  129. Cho, H.; Kwak, J.; Lim, J.; Park, M.; Lee, D.; Bae, W.K.; Kim, Y.S.; Char, K.; Lee, S.; Lee, C. Soft Contact Transplanted Nanocrystal Quantum Dots for Light-Emitting Diodes: Effect of Surface Energy on Device Performance. ACS Appl. Mater. Interfaces 2015, 7, 10828–10833. [Google Scholar] [CrossRef]
  130. Roh, H.; Ko, D.; Shin, D.Y.; Chang, J.H.; Hahm, D.; Bae, W.K.; Lee, C.; Kim, J.Y.; Kwak, J. Enhanced Performance of Pixelated Quantum Dot Light-Emitting Diodes by Inkjet Printing of Quantum Dot–Polymer Composites. Adv. Opt. Mater. 2021, 9, 2002129. [Google Scholar] [CrossRef]
  131. Yang, J.; Hahm, D.; Kim, K.; Rhee, S.; Lee, M.; Kim, S.; Chang, J.H.; Park, H.W.; Lim, J.; Lee, M.; et al. High-Resolution Patterning of Colloidal Quantum Dots via Non-Destructive, Light-Driven Ligand Crosslinking. Nat. Commun. 2020, 11, 2874. [Google Scholar] [CrossRef] [PubMed]
  132. Wood, V.; Panzer, M.J.; Chen, J.; Bradley, M.S.; Halpert, J.E.; Bawendi, M.C.; Bulović, V. Inkjet-Printed Quantum Dot-Polymer Composites for Full-Color AC-Driven Displays. Adv. Mater. 2009, 21, 2151–2155. [Google Scholar] [CrossRef]
  133. Haverinen, H.M.; Myllylä, R.A.; Jabbour, G.E. Inkjet Printing of Light Emitting Quantum Dots. Appl. Phys. Lett. 2009, 94, 073108. [Google Scholar] [CrossRef]
  134. Haverinen, H.M.; Myllylä, R.A.; Jabbour, G.E.; Cheng, M. Inkjet Printed RGB Quantum Dot-Hybrid LED. J. Disp. Technol. 2010, 6, 87–89. [Google Scholar] [CrossRef]
  135. Still, T.; Yunker, P.J.; Yodh, A.G. Surfactant-Induced Marangoni Eddies Alter the Coffee-Rings of Evaporating Colloidal Drops. Langmuir 2012, 28, 4984–4988. [Google Scholar] [CrossRef] [PubMed]
  136. Jiang, C.; Zhong, Z.; Liu, B.; He, Z.; Zou, J.; Wang, L.; Wang, J.; Peng, J.; Cao, Y. Coffee-Ring-Free Quantum Dot Thin Film Using Inkjet Printing from a Mixed-Solvent System on Modified ZnO Transport Layer for Light-Emitting Devices. ACS Appl. Mater. Interfaces 2016, 8, 26162–26168. [Google Scholar] [CrossRef] [PubMed]
  137. Wang, J.; Dong, T.; Zhong, Z.; Zheng, H.; Xu, W.; Ying, L.; Wang, J.; Peng, J.; Cao, Y. Uniform Inkjet-Printed Films with Single Solvent. Thin Solid Films 2018, 667, 21–27. [Google Scholar] [CrossRef]
  138. Yu, X.; Xing, R.; Peng, Z.; Lin, Y.; Du, Z.; Ding, J.; Wang, L.; Han, Y. To Inhibit Coffee Ring Effect in Inkjet Printing of Light-Emitting Polymer Films by Decreasing Capillary Force. Chin. Chem. Lett. 2019, 30, 135–138. [Google Scholar] [CrossRef]
  139. Li, H.; Duan, Y.; Shao, Z.; Zhang, G.; Li, H.; Huang, Y.; Yin, Z. QLEDs: High-Resolution Pixelated Light Emitting Diodes Based on Electrohydrodynamic Printing and Coffee-Ring-Free Quantum Dot Film. Adv. Mater. Technol. 2020, 5, 2000401. [Google Scholar] [CrossRef]
  140. Xiang, C.; Wu, L.; Lu, Z.; Li, M.; Wen, Y.; Yang, Y.; Liu, W.; Zhang, T.; Cao, W.; Tsang, S.W.; et al. High Efficiency and Stability of Ink-Jet Printed Quantum Dot Light Emitting Diodes. Nat. Commun. 2020, 11, 1646. [Google Scholar] [CrossRef] [Green Version]
  141. Xie, L.; Yang, J.; Zhao, W.; Yi, Y.Q.Q.; Liu, Y.; Su, W.; Li, Q.; Lei, W.; Cui, Z. High-Performance Inkjet-Printed Blue QLED Enabled by Crosslinked and Intertwined Hole Transport Layer. Adv. Opt. Mater. 2022, 10, 2200935. [Google Scholar] [CrossRef]
  142. Mei, W.; Zhang, Z.; Zhang, A.; Li, D.; Zhang, X.; Wang, H.; Chen, Z.; Li, Y.; Li, X.; Xu, X. High-Resolution, Full-Color Quantum Dot Light-Emitting Diode Display Fabricated via Photolithography Approach. Nano Res. 2020, 13, 2485–2491. [Google Scholar] [CrossRef]
  143. Myeong, S.; Chon, B.; Kumar, S.; Son, H.J.; Kang, S.O.; Seo, S. Quantum Dot Photolithography Using a Quantum Dot Photoresist Composed of an Organic-Inorganic Hybrid Coating Layer. Nanoscale Adv. 2022, 4, 1080–1087. [Google Scholar] [CrossRef] [PubMed]
  144. Wang, Y.; Fedin, I.; Zhang, H.; Talapin, D.V. Direct Optical Lithography of Functional Inorganic Nanomaterials. Science 2017, 357, 385–388. [Google Scholar] [CrossRef] [PubMed] [Green Version]
  145. Wang, Y.; Pan, J.A.; Wu, H.; Talapin, D.V. Direct Wavelength-Selective Optical and Electron-Beam Lithography of Functional Inorganic Nanomaterials. ACS Nano 2019, 13, 13917–13931. [Google Scholar] [CrossRef] [Green Version]
  146. Cho, H.; Pan, J.A.; Wu, H.; Lan, X.; Coropceanu, I.; Wang, Y.; Cho, W.; Hill, E.A.; Anderson, J.S.; Talapin, D.V. Direct Optical Patterning of Quantum Dot Light-Emitting Diodes via In Situ Ligand Exchange. Adv. Mater. 2020, 32, 2003805. [Google Scholar] [CrossRef]
  147. Park, J.S.; Kyhm, J.; Kim, H.H.; Jeong, S.; Kang, J.; Lee, S.E.; Lee, K.T.; Park, K.; Barange, N.; Han, J.; et al. Alternative Patterning Process for Realization of Large-Area, Full-Color, Active Quantum Dot Display. Nano Lett. 2016, 16, 6946–6953. [Google Scholar] [CrossRef]
  148. Hahm, D.; Lim, J.; Kim, H.; Shin, J.W.; Hwang, S.; Rhee, S.; Chang, J.H.; Yang, J.; Lim, C.H.; Jo, H.; et al. Direct Patterning of Colloidal Quantum Dots with Adaptable Dual-Ligand Surface. Nat. Nanotechnol. 2022, 17, 952–958. [Google Scholar] [CrossRef]
  149. Kong, Y.L.; Tamargo, I.A.; Kim, H.; Johnson, B.N.; Gupta, M.K.; Koh, T.W.; Chin, H.A.; Steingart, D.A.; Rand, B.P.; McAlpine, M.C. 3D Printed Quantum Dot Light-Emitting Diodes. Nano Lett. 2014, 14, 7017–7023. [Google Scholar] [CrossRef]
  150. Bae, J.; Lee, S.; Ahn, J.; Kim, J.H.; Wajahat, M.; Chang, W.S.; Yoon, S.Y.; Kim, J.T.; Seol, S.K.; Pyo, J. 3D-Printed Quantum Dot Nanopixels. ACS Nano 2020, 14, 10993–11001. [Google Scholar] [CrossRef]
  151. Kim, B.H.; Onses, M.S.; Lim, J.B.; Nam, S.; Oh, N.; Kim, H.; Yu, K.J.; Lee, J.W.; Kim, J.H.; Kang, S.K.; et al. High-Resolution Patterns of Quantum Dots Formed by Electrohydrodynamic Jet Printing for Light-Emitting Diodes. Nano Lett. 2015, 15, 969–973. [Google Scholar] [CrossRef] [PubMed] [Green Version]
  152. Guo, Y.; Moffitt, M.G. “Smart” Self-Assembled Quantum Dots Regulate and Stabilize Structure in Phase-Separated Polymer Blends. Chem. Mater. 2007, 19, 6581–6587. [Google Scholar] [CrossRef]
  153. Zhao, J.; Chen, L.; Li, D.; Shi, Z.; Liu, P.; Yao, Z.; Yang, H.; Zou, T.; Zhao, B.; Zhang, X.; et al. Large-Area Patterning of Full-Color Quantum Dot Arrays beyond 1000 Pixels per Inch by Selective Electrophoretic Deposition. Nat. Commun. 2021, 12, 4603. [Google Scholar] [CrossRef] [PubMed]
  154. Kang, H.L.; Kang, J.; Won, J.K.; Jung, S.M.; Kim, J.; Park, C.H.; Ju, B.K.; Kim, M.G.; Park, S.K. Spatial Light Patterning of Full Color Quantum Dot Displays Enabled by Locally Controlled Surface Tailoring. Adv. Opt. Mater. 2018, 6, 1701335. [Google Scholar] [CrossRef]
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Figure 1. AM-QLEDs driven by various oxide TFTs. (a) Green-emitting 4-inch display driven by solution-processed Li-doped ZnO TFTs and its single-pixel structure (reproduced from [32] with permission from Wiley). (b) Full-color 14-inch display driven by IGZO TFTs and its single-pixel structure (reproduced from [22] with permission from Wiley).
Figure 1. AM-QLEDs driven by various oxide TFTs. (a) Green-emitting 4-inch display driven by solution-processed Li-doped ZnO TFTs and its single-pixel structure (reproduced from [32] with permission from Wiley). (b) Full-color 14-inch display driven by IGZO TFTs and its single-pixel structure (reproduced from [22] with permission from Wiley).
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Figure 2. Schematic illustration for AM driving: (a) Typical 2T1C circuit and (b) 6T1C pixel compensation circuit (reproduced from [33] with permission from Elsevier).
Figure 2. Schematic illustration for AM driving: (a) Typical 2T1C circuit and (b) 6T1C pixel compensation circuit (reproduced from [33] with permission from Elsevier).
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Figure 3. QLED device architecture with a schematic energy band diagram: (a) A normal structure and (b) an inverted structure.
Figure 3. QLED device architecture with a schematic energy band diagram: (a) A normal structure and (b) an inverted structure.
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Figure 5. Schematic illustration of various QD patterning methods: (a) Contact transfer printing of QDs using a PDMS stamp (Reproduced from [129] with permission from American Chemical Society). (b) Inkjet printing of QD solution into subpixels (Reproduced from [130] with permission from Wiley). (c) UV-induced ligand crosslinking process for direct patterning of the QD film (Reproduced from [131] with permission from Springer Nature).
Figure 5. Schematic illustration of various QD patterning methods: (a) Contact transfer printing of QDs using a PDMS stamp (Reproduced from [129] with permission from American Chemical Society). (b) Inkjet printing of QD solution into subpixels (Reproduced from [130] with permission from Wiley). (c) UV-induced ligand crosslinking process for direct patterning of the QD film (Reproduced from [131] with permission from Springer Nature).
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Figure 6. Monolithically integrated TFT–QLED devices: (a) Schematic cross-sectional diagram of inkjet-printed TFT–QLED pixel, the morphology of the inkjet-printed oxide film, the pixel structure, and a demonstration of the 2T1C-structured AM-QLED (Reproduced from [24] with permission from American Chemical Society). (b) Schemes of TFT–QLED using the multilayered MoS2 TFT with ODTS-SAM on the back channel, current–voltage characteristics along with the driving current level, and luminance change (Reproduced from [23] with permission from Wiley). (c) Schematic structure of MoTe2 TFT-driven QLED with luminance changes, current–voltage characteristics of type-converted TFTs via PLL treatment, current–voltage–luminance characteristics of the TFT–QLED device, and their stability (Reproduced from [25] with permission from Wiley).
Figure 6. Monolithically integrated TFT–QLED devices: (a) Schematic cross-sectional diagram of inkjet-printed TFT–QLED pixel, the morphology of the inkjet-printed oxide film, the pixel structure, and a demonstration of the 2T1C-structured AM-QLED (Reproduced from [24] with permission from American Chemical Society). (b) Schemes of TFT–QLED using the multilayered MoS2 TFT with ODTS-SAM on the back channel, current–voltage characteristics along with the driving current level, and luminance change (Reproduced from [23] with permission from Wiley). (c) Schematic structure of MoTe2 TFT-driven QLED with luminance changes, current–voltage characteristics of type-converted TFTs via PLL treatment, current–voltage–luminance characteristics of the TFT–QLED device, and their stability (Reproduced from [25] with permission from Wiley).
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Baek, G.W.; Kim, Y.J.; Lee, M.; Kwon, Y.; Chun, B.; Park, G.; Seo, H.; Yang, H.; Kwak, J. Progress in the Development of Active-Matrix Quantum-Dot Light-Emitting Diodes Driven by Non-Si Thin-Film Transistors. Materials 2022, 15, 8511. https://doi.org/10.3390/ma15238511

AMA Style

Baek GW, Kim YJ, Lee M, Kwon Y, Chun B, Park G, Seo H, Yang H, Kwak J. Progress in the Development of Active-Matrix Quantum-Dot Light-Emitting Diodes Driven by Non-Si Thin-Film Transistors. Materials. 2022; 15(23):8511. https://doi.org/10.3390/ma15238511

Chicago/Turabian Style

Baek, Geun Woo, Yeon Jun Kim, Minhyung Lee, Yeunwoo Kwon, Beomsoo Chun, Ganghyun Park, Hansol Seo, Heesun Yang, and Jeonghun Kwak. 2022. "Progress in the Development of Active-Matrix Quantum-Dot Light-Emitting Diodes Driven by Non-Si Thin-Film Transistors" Materials 15, no. 23: 8511. https://doi.org/10.3390/ma15238511

APA Style

Baek, G. W., Kim, Y. J., Lee, M., Kwon, Y., Chun, B., Park, G., Seo, H., Yang, H., & Kwak, J. (2022). Progress in the Development of Active-Matrix Quantum-Dot Light-Emitting Diodes Driven by Non-Si Thin-Film Transistors. Materials, 15(23), 8511. https://doi.org/10.3390/ma15238511

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