Ying Chen

Bio: Ying Chen is an academic researcher from Iowa State University. The author has contributed to research in topics: OLED & PEDOT:PSS. The author has an hindex of 15, co-authored 26 publications receiving 1123 citations. Previous affiliations of Ying Chen include University of Florida.

High‐Efficiency Solution‐Processed Small Molecule Electrophosphorescent Organic Light‐Emitting Diodes

Abstract: Extensive research on organic light-emitting diodes (OLEDs) continues due to their promise in applications such as fl at panel displays and solid state lighting. [ 1–5 ] Commonly, thermal high-vacuum evaporation technology is used for fabrication of small molecule-based OLEDs (SMOLEDs) and solution processing technology is used for those based on polymers (PLEDs). Thermal evaporation deposition enables complicated multilayer device architectures and renders excellent devices with high effi ciencies. [ 6 , 7 ] In contrast, solution-based deposition limits fabrication of composite device structures because the solvent used for one layer can redissolve or otherwise damage the previous layers. [ 8 ] Therefore, thermally evaporated SMOLEDs are typically more effi cient and longer-lived than solution-processed PLEDs. However, thermal evaporation deposition has its own disadvantages. First, it requires high vacuum and is consequently much more costly. Second, making multidopant OLEDs, such as white OLEDs (WOLEDs), requires precise control of the doping concentration of each dopant in the emitting layer (EML) to obtain the desired emission. [ 9 , 10 ] These reasons usually lead to a fabrication process of greater complexity and higher cost. On the other hand, solution processing, such as spin-coating, inkjet printing, and screen printing, is advantageous over thermal evaporation processing, due to its low-cost and large area manufacturability. [ 10 , 11 ] Additionally, it is possible to realize co-doping of several dopants by mixing the dopants and host material in solution. Hence, the fabrication of SMOLEDs via a solution process is of great importance. To that end, we demonstrate high effi ciency (forward power and luminous effi ciencies up to 60 lm W − 1 and 69 Cd A − 1 , respectively) spin-coated electrophosphorescent SMOLEDs based on greenemitting tris[2-(p-tolyl)pyridine] iridium(III) (Ir(mppy) 3 ) doped into a 4,4’-bis(9-carbazolyl)-biphenyl (CBP) host, probably due to the materials and fi lm morphology. This is the highest reported effi ciency of any solution-processed OLED and among the highest of any OLED without outcoupling enhancement. The

Nickel Oxide Hole Injection/Transport Layers for Efficient Solution-Processed Organic Light-Emitting Diodes

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...

Review of recent progress in multilayer solution-processed 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.

Bridging the efficiency gap: fully bridged dinuclear Cu(I)-complexes for singlet harvesting in high-efficiency OLEDs.

Abstract: The substitution of rare metals such as iridium and platinum in light-emitting materials is a key step to enable low-cost mass-production of organic light-emitting diodes (OLEDs). Here, it is demonstrated that using a solution-processed, fully bridged dinuclear Cu(I)-complex can yield very high efficiencies. An optimized device gives a maximum external quantum efficiency of 23 ± 1% (73 ± 2 cd A(-1) ).

Extremely Efficient Indium–Tin‐Oxide‐Free Green Phosphorescent Organic Light‐Emitting Diodes

Abstract: This paper demonstrates extremely efficient (ηP,max = 118 lm W−1) ITO-free green phosphorescent OLEDs (PHOLEDs) with multilayered, highly conductive poly(3,4-ethylenedioxythiophene): poly(styrenesulfonate) (PEDOT:PSS) films as the anode. The efficiency is obtained without any outcoupling-enhancing structures and is 44% higher than the 82 lm W−1 of similar optimized ITO-anode PHOLEDs. Detailed simulations show that this improvement is due largely to the intrinsically enhanced outcoupling that results from a weak microcavity effect.

All-organic thermally activated delayed fluorescence materials for organic light-emitting diodes

Abstract: Thermally activated delayed fluorescence (TADF) emitters, which produce light by harvesting both singlet and triplet excitons without noble metals, are emerging as next-generation organic electroluminescent materials. In the past few years, there have been rapid advances in molecular design criteria, our understanding of the photophysics underlying TADF and the applications of TADF materials as emitters in organic light-emitting diodes (OLEDs). This topic is set to remain at the forefront of research in optoelectronic organic materials for the foreseeable future. In this Review, we focus on state-of-the-art materials design and understanding of the photophysical processes, which are being leveraged to optimize the performance of OLED devices. Notably, we also appraise dendritic and polymeric TADF emitters — macromolecular materials that offer the potential advantages of low cost, solution processable and large-area OLED fabrication. Thermally activated delayed fluorescence (TADF) emitters are promising electroluminescent materials for next-generation organic light-emitting diodes (OLEDs). In this Review, the molecular design, photophysical characteristics and OLEDs composed of small-molecule, dendritic and polymeric TADF emitters are discussed.

Effective Approaches to Improve the Electrical Conductivity of PEDOT:PSS: A Review

Abstract: The rapid development of novel organic technologies has led to significant applications of the organic electronic devices such as light-emitting diodes, solar cells, and field-effect transistors. There is a great need for conducting polymers with high conductivity and transparency to act as the charge transport layer or electrical interconnect in organic devices. Poly(3,4-ethylenedioxythiophene): poly(styrenesulfonic acid) (PEDOT:PSS), well-known as the most remarkable conducting polymer, has this role owing to its good film-forming properties, high transparency, tunable conductivity, and excellent thermal stability. In this Review, various of interesting physical and chemical approaches that can effectively improve the electrical conductivity of PEDOT:PSS are summarized, focusing especially on the mechanism of the conductivity enhancement as well as applications of PEDOT:PSS films. Prospects for future research efforts are also provided. It is expected that PEDOT:PSS films with high conductivity and transparency could be the focus of future organic electronic materials breakthroughs.

High‐Performance and Environmentally Stable Planar Heterojunction Perovskite Solar Cells Based on a Solution‐Processed Copper‐Doped Nickel Oxide Hole‐Transporting Layer

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

Spectroscopic and Device Aspects of Nanocrystal Quantum Dots

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...

Quantum-Dot Light-Emitting Diodes for Large-Area Displays: Towards the Dawn of Commercialization.

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.