V. Y. Lee

Bio: V. Y. Lee is an academic researcher from IBM. The author has contributed to research in topics: Superconductivity & Oxygen. The author has an hindex of 35, co-authored 71 publications receiving 5636 citations. Previous affiliations of V. Y. Lee include Northwest University (United States).

Discovery of a Neutral-to-Ionic Phase Transition in Organic Materials

Abstract: A systematic study of mixed stacked organic charge-transfer compounds shows that these materials are either neutral or ionic and that they range from being near the neutral-ionic boundary to being far away. Under pressure, several neutral compounds near this boundary are found to undergo a reversible phase transition to an ionic ground state. This is the first observation of a neutral-to-ionic transition in any kind of material.

Bulk superconductivity at 125 K in Tl2Ca2Ba2Cu3Ox.

Abstract: Bulk superconductivity is reported in T12Ca2 Ba2 Cu3 Ox with a transition to zero resistance at ≃ 125 K, the highest transition temperature (Tc) yet found. Transmission electron spectroscopy shows that the unit cell is body-centered tetragonal and contains trilayer Cu perovskitelike units separated by bilayer TI-O units. (T c in this material varies from 118 to 125 K depending on preparation conditions. A high density of perovskitelike bilayer intergrowths are observed in the 118-K material, which we speculate result in the decreased (T c. A second structure containing only bilayer perovskitelike units—TI2 Ca1 Ba2Cu2Ox—is a bulk superconductor with Tv ranging from 95 to 108 K.

Tl 1 Ca n − 1 Ba 2 Cu n O 2 n + 3 ( n = 1 , 2 , 3 ): A New Class of Crystal Structures Exhibiting Volume Superconductivity at up to ≃110 K

Abstract: We report the discovery of three new phases in the Tl-Ca-Ba-Cu-O system, Tl/sub 1/Ca/sub n//sub -1/Ba/sub 2/Cu/sub n/O/sub 2//sub n//sub +3/ (n = 1,2,3), one of which (n = 3) exhibits bulk superconductivity at approx. =110 K. The crystal structures of these new materials are closely related to that of Tl/sub 2/Ca/sub 2/Ba/sub 2/Cu/sub 3/O/sub x/, the recently discovered 125-K superconductor. All of these compounds contain Cu perovskitelike units, but whereas these are separated by bilayer Tl-O sheets in the 125-K material these are separated by monolayer Tl-O sheets in the new structures, enabling an examination of the role played by the coupling between successive Cu perovskite units on superconducting properties.

Thermally Stable Blue-Light-Emitting Copolymers of Poly(alkylfluorene)

Abstract: We have prepared a variety of high molecular weight, thermally stable, blue-light-emitting random copolymers of 9,9-di-n-hexylfluorene by nickel(0)-mediated polymerization. The copolymers are readily soluble and easily processable from organic solvents. Both the polymer and electronic properties may be tuned by selection of comonomer structure. The electronic properties also vary with composition and film morphology. A blue-light-emitting device has been prepared using ionic salts for electrochemical doping.

Organic Glasses: A New Class of Photorefractive Materials

Abstract: The performance of amorphous organic photorefractive (PR) materials in applications such as optical data storage is generally limited by the concentration of active molecules (chromophores) that can be incorporated into the host without forming a crystalline material with poor optical quality. In polymeric PR systems described previously, performance has been limited by the necessity of devoting a large fraction of the material to inert polymer and plasticizing components in order to ensure compositional stability. A new class of organic PR materials composed of multifunctional glass-forming organic chromophores is described that have long-term stability and greatly improved PR properties.

Synthesis of Light-Emitting Conjugated Polymers for Applications in Electroluminescent Devices

Abstract: A review was presented to demonstrate a historical description of the synthesis of light-emitting conjugated polymers for applications in electroluminescent devices. Electroluminescence (EL) was first reported in poly(para-phenylene vinylene) (PPV) in 1990 and researchers continued to make significant efforts to develop conjugated materials as the active units in light-emitting devices (LED) to be used in display applications. Conjugated oligomers were used as luminescent materials and as models for conjugated polymers in the review. Oligomers were used to demonstrate a structure and property relationship to determine a key polymer property or to demonstrate a technique that was to be applied to polymers. The review focused on demonstrating the way polymer structures were made and the way their properties were controlled by intelligent and rational and synthetic design.

The electroluminescence of organic materials

Abstract: This article provides a review about electroluminescence from organic materials and deals in detail with organic light-emitting diodes (OLEDs), light-emitting electro-chemical cells (LECs) and electrogenerated chemilumi-nescence (ECL) reflecting different electrooptical appli-cations of conjugated materials. It is written from an organic chemist's point of view and pays particular attention to the development of organic materials involved in corresponding devices. In recent years a substantial amount of both academic and industrial research has been directed to organic electroluminescence in an effort to improve the processability and tunability of organic materials and the longevity of OLEDs and LECs. On the eve of the commercialization of organic electrolumi-nescence this review provides an overview of lifetimes and efficiencies attained and reflects materials and device concepts developed over the last decade. In this context electrogenerated chemiluminescence is discussed with respect to its importance as a versatile tool to simulate the fundamental electrochemical processes in OLEDs.

Semiconducting Polyfluorenes—Towards Reliable Structure–Property Relationships

Abstract: Alkylsabstituted polyfluorenes have emerged as a very attractive class of conju gated polymers, especially for display applications, owing to their pure blue and efficient electroluminescence coupled with a high charge-carrier mobility and good processability. The availability of specific and highly regroselective coupling reactions provides a rich variety of taifored polyfluorene-type paly mers and copolymers. The focus of this review, therefore, is on reliable structure-property relationships regarding (i) the interplay of substitution pattern, solid state morphology, and optical/electronic properties, and (ii) the key role of degradation-induced keto defect sites in fluorerse-type polymers, and strategies for obtaining defect-free polyfluorenes.

Rational Design of High Performance Conjugated Polymers for Organic Solar Cells

Abstract: The research on the polymer-based solar cells (PSCs) has attracted an increasing amount of attention in recent years because PSCs pose potential advantages over mainstream inorganic-based solar cells, such as significantly reduced material/fabrication costs, flexible substrates, and light weight of finished solar cells. The research community has made great progress in the field of bulk heterojunction (BHJ) polymer solar cells since its inception in 1995. The power conversion efficiency (PCE), a key parameter to assess the performance of solar cells, has increased from 1% in the 1990s to over 8% just recently. These great advances are mainly fueled by the development of conjugated polymers used as the electron-donating materials in BHJ solar cells. In this Perspective, we first briefly review the progress on the design of conjugated polymers for polymer solar cells in the past 16 years. Since a conjugated polymer can be arbitrarily divided into three constituting components—the conjugated backbone, the si...