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Shuyi Liu

Bio: Shuyi Liu is an academic researcher from North Carolina State University. The author has contributed to research in topics: OLED & Layer (electronics). The author has an hindex of 9, co-authored 19 publications receiving 455 citations. Previous affiliations of Shuyi Liu include University of Florida & Tsinghua University.

Papers
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Journal ArticleDOI
Shuyi Liu1, Rui Liu1, Ying Chen1, Szuheng Ho1, Jong H. Kim1, Franky So1 
TL;DR: In this article, the hole injection efficiency of solution-processed nickel oxides (s-NiOx) was compared with poly(3,4-ethylenedioxythiophene):poly(styrenesulfonate) (PEDOT:PSS) hole injection layers (HIL).
Abstract: Solution-processed nickel oxides (s-NiOx) are used as hole injection and transport layers in solution-processed organic light-emitting diodes (OLEDs). By increasing the annealing temperature, the nickel acetate precursor fully decomposes and the s-NiOx film shows larger crystalline grain sizes, which lead to better hole injection and transport properties. UV–ozone treatment on the s-NiOx surface is carried out to further modify its surface chemistry, improving the hole injection efficiency. The introduction of more dipolar species of nickel oxy-hydroxide (NiO(OH)) is evidenced after the treatment. Dark injection–space charge limited (DI–SCL) transient measurement was carried out to compare the hole injection efficiency of s-NiOx and poly(3,4-ethylenedioxythiophene):poly(styrenesulfonate) (PEDOT:PSS) hole injection layers (HIL). The UV–ozone treated s-NiOx shows significantly better hole injection, with a high injection efficiency of 0.8. With a p-type thin film transistor (TFT) configuration, the high-tem...

181 citations

Journal ArticleDOI
TL;DR: In this article, the authors discuss the use of cross-linkable organic materials, metal oxides, and orthogonal solvent systems to deposit various functional layers in an organic light-emitting diodes.
Abstract: Organic light-emitting diodes (OLEDs) have become a promising candidate for lighting and display applications. High efficiency OLEDs require a multilayer device architecture to provide exciton confinement and balance charge transport. Conventional OLEDs are made by vacuum process, and the manufacturing cost can be reduced by solution processing. However, unlike vacuum-deposited OLEDs, solution-processed multilayer OLEDs are more challenging to make. The key for multilayer solution processing is to have the layer structure which can withstand solvents used in subsequent processing. We review the materials’ strategies to make multilayer solution-processed OLEDs. Specifically, we will discuss the use of cross-linkable organic materials, metal oxides, and orthogonal solvent systems to deposit various functional layers in an OLED.

147 citations

Journal ArticleDOI
TL;DR: In this paper, the exciton quenching properties of solution-processed nickel oxide (NiOx) and vanadium oxide (VOx) are studied by measuring the photoluminescence (PL) of a thin emitting layer (EML) deposited on top of the metal oxides.
Abstract: The exciton quenching properties of solution-processed nickel oxide (NiOx) and vanadium oxide (VOx) are studied by measuring the photoluminescence (PL) of a thin emitting layer (EML) deposited on top of the metal oxides. Strong exciton quenching is evidenced at the metal oxide/EML interface, which is proved to be detrimental to the performance of optoelectronic devices. With a thin polyvinylpyrrolidone (PVP) passivation polymer adsorbed on top of metal oxides, the PL quenching is found to be effectively suppressed. A short UV–O3 treatment on top of the PVP-passivated metal oxides turns out to be a key procedure to trigger the chemical binding between the PVP passivation polymer and the metal oxide surface species, which turns out to be necessary for efficient hole injection and extraction for organic light emitting diodes (OLEDs) and solar cell devices, respectively. With the PVP passivation layer followed by UV–O3 treatment, the OLEDs incorporating NiOx as a hole transport layer (HTL) shows a record curr...

62 citations

Journal ArticleDOI
TL;DR: By controlling the surface wetting properties of a polydimethylsiloxane (PDMS) release template, a multilayer patterning and transferring process can be realized, resulting in a fine-patterned, smooth, and uniform AgNWs mesh/poly(3,4-ethylenedioxythiophene) polystyrenesulfonate ( PEDOT PSS) composite electrode.
Abstract: Silver nanowires (AgNWs) mesh has been used as transparent electrodes in optoelectronic devices. However, the lack of practical patterning techniques for the random percolating nanowire network has limited its applications in devices where a well-defined pixel is required. Here, by controlling the surface wetting properties of a polydimethylsiloxane (PDMS) release template, we are able to pattern the random AgNWs network with uniform conducting property; and due to the hydrophobic recovery nature of PDMS, a multilayer patterning and transferring process can be realized, resulting in a fine-patterned, smooth, and uniform AgNWs mesh/poly(3,4-ethylenedioxythiophene) polystyrenesulfonate (PEDOT:PSS) composite electrode. A thermal-evaporated organic light-emitting diode (OLED) is directly fabricated onto the patterned AgNWs/PEDOT:PSS composite electrode. The device shows well-defined pixel edges and a uniformly lighted pixel area. A uniform OLED with very low leakage current is realized. The enhanced efficienc...

45 citations

Journal ArticleDOI
TL;DR: This work reports a successful synthesis of very large mono-dispersed PbS NPs having a diameter up to 16 nm by multiple injections and to demonstrate the applications of such large QDs, broadband heterojunction photodetectors are fabricated with the large P bS QDs of an absorption peak at 2100 nm.
Abstract: Lead sulfide nanoparticles (PbS NPs) are used in the short-wavelength infrared photodetectors because of their excellent photosensitivity, band gap tunability, and solution processability. It has been a challenge to synthesize high-quality PbS NPs with an absorption peak beyond 2000 nm. In this work, using PbS seed crystals with an absorption peak at 1960 nm, we report a successful synthesis of very large monodispersed PbS NPs having a diameter up to 16 nm by multiple injections. The resulting NPs have an absorption peak over 2500 nm with a small full width at half-maximum of 24 meV. To demonstrate the applications of such large quantum dots (QDs), broadband heterojunction photodetectors are fabricated with the large PbS QDs of an absorption peak at 2100 nm. The resulting devices have an external quantum efficiency (EQE) of 25% (over 50% internal quantum efficiency) at 2100 nm corresponding to a responsivity of 0.385 A/W and an EQE of ∼60% in the visible range.

31 citations


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TL;DR: An effective approach to significantly increase the electrical conductivity of a NiOx hole-transporting layer (HTL) to achieve high-efficiency planar heterojunction perovskite solar cells is demonstrated.
Abstract: An effective approach to significantly increase the electrical conductivity of a NiOx hole-transporting layer (HTL) to achieve high-efficiency planar heterojunction perovskite solar cells is demonstrated Perovskite solar cells based on using Cu-doped NiOx HTL show a remarkably improved power conversion efficiency up to 1540% due to the improved electrical conductivity and enhanced perovskite film quality General applicability of Cu-doped NiOx to larger bandgap perovskites is also demonstrated in this study

743 citations

Journal ArticleDOI
TL;DR: Recent advances in nanocrystal research related to applications of QD materials in lasing, light-emitting diodes (LEDs), and solar energy conversion are examined.
Abstract: The field of nanocrystal quantum dots (QDs) is already more than 30 years old, and yet continuing interest in these structures is driven by both the fascinating physics emerging from strong quantum confinement of electronic excitations, as well as a large number of prospective applications that could benefit from the tunable properties and amenability toward solution-based processing of these materials. The focus of this review is on recent advances in nanocrystal research related to applications of QD materials in lasing, light-emitting diodes (LEDs), and solar energy conversion. A specific underlying theme is innovative concepts for tuning the properties of QDs beyond what is possible via traditional size manipulation, particularly through heterostructuring. Examples of such advanced control of nanocrystal functionalities include the following: interface engineering for suppressing Auger recombination in the context of QD LEDs and lasers; Stokes-shift engineering for applications in large-area luminesce...

703 citations

Journal ArticleDOI
TL;DR: A Progress Report, covering interdisciplinary aspects including material chemistry of quantum dots and charge-transporting layers, optimization and mechanism studies of prototype devices and processing techniques to produce large-area and high-resolution red-green-blue pixel arrays, identifies a few key challenges facing the development of active-matrix QLED displays.
Abstract: Quantum dots are a unique class of emitters with size-tunable emission wavelengths, saturated emission colors, near-unity luminance efficiency, inherent photo- and thermal- stability and excellent solution processability. Quantum dots have been used as down-converters for back-lighting in liquid-crystal displays to improve color gamut, leading to the booming of quantum-dot televisions in consumer market. In the past few years, efficiency and lifetime of electroluminescence devices based on quantum dots achieved tremendous progress. These encouraging facts foreshadow the commercialization of quantum-dot light-emitting diodes (QLEDs), which promises an unprecedented generation of cost-effective, large-area, energy-saving, wide-color-gamut, ultra-thin and flexible displays. Here we provide a Progress Report, covering interdisciplinary aspects including material chemistry of quantum dots and charge-transporting layers, optimization and mechanism studies of prototype devices and processing techniques to produce large-area and high-resolution red-green-blue pixel arrays. We also identify a few key challenges facing the development of active-matrix QLED displays.

548 citations

Journal ArticleDOI
TL;DR: P-type oxides still lag in performance behind their n-type counterparts, which have entered volume production in the display market, and recent successes along with the hurdles that stand in the way of commercial success of p-type oxide semiconductors are presented.
Abstract: The development of transparent p-type oxide semiconductors with good performance may be a true enabler for a variety of applications where transparency, power efficiency, and greater circuit complexity are needed. Such applications include transparent electronics, displays, sensors, photovoltaics, memristors, and electrochromics. Hence, here, recent developments in materials and devices based on p-type oxide semiconductors are reviewed, including ternary Cu-bearing oxides, binary copper oxides, tin monoxide, spinel oxides, and nickel oxides. The crystal and electronic structures of these materials are discussed, along with approaches to enhance valence-band dispersion to reduce effective mass and increase mobility. Strategies to reduce interfacial defects, off-state current, and material instability are suggested. Furthermore, it is shown that promising progress has been made in the performance of various types of devices based on p-type oxides. Several innovative approaches exist to fabricate transparent complementary metal oxide semiconductor (CMOS) devices, including novel device fabrication schemes and utilization of surface chemistry effects, resulting in good inverter gains. However, despite recent developments, p-type oxides still lag in performance behind their n-type counterparts, which have entered volume production in the display market. Recent successes along with the hurdles that stand in the way of commercial success of p-type oxide semiconductors are presented.

507 citations

Journal ArticleDOI
01 Nov 2016-Small
TL;DR: Recent progress on the main applications reported for MNW networks of any sort (silver, copper, gold, core-shell nanowires) are investigated and some of the most impressive outcomes are pointed out.
Abstract: Transparent electrodes attract intense attention in many technological fields, including optoelectronic devices, transparent film heaters and electromagnetic applications. New generation transparent electrodes are expected to have three main physical properties: high electrical conductivity, high transparency and mechanical flexibility. The most efficient and widely used transparent conducting material is currently indium tin oxide (ITO). However the scarcity of indium associated with ITO's lack of flexibility and the relatively high manufacturing costs have a prompted search into alternative materials. With their outstanding physical properties, metallic nanowire (MNW)-based percolating networks appear to be one of the most promising alternatives to ITO. They also have several other advantages, such as solution-based processing, and are compatible with large area deposition techniques. Estimations of cost of the technology are lower, in particular thanks to the small quantities of nanomaterials needed to reach industrial performance criteria. The present review investigates recent progress on the main applications reported for MNW networks of any sort (silver, copper, gold, core-shell nanowires) and points out some of the most impressive outcomes. Insights into processing MNW into high-performance transparent conducting thin films are also discussed according to each specific application. Finally, strategies for improving both their stability and integration into real devices are presented.

445 citations