Byung Jun Jung

Bio: Byung Jun Jung is an academic researcher from Seoul National University. The author has contributed to research in topics: Fluorene & Polyfluorene. The author has an hindex of 34, co-authored 93 publications receiving 3666 citations. Previous affiliations of Byung Jun Jung include KAIST & Johns Hopkins University.

Ladder-type oligo-p-phenylene-containing copolymers with high open-circuit voltages and ambient photovoltaic activity

Abstract: Ladder-type oligo-p-phenylene containing donor-acceptor copolymers are disclosed. The ladder-type oligo-p-phenylene can be used as an electron donor unit in the disclosed copolymers to provide a deeper highest occupied molecular orbital (HOMO) level for obtaining polymeric solar cells having a higher open-circuit voltage. Particular electron-accepting units, e.g., a divalent fused-ring heterocyclic moiety selected from the group consisting of a substituted or unsubstituted benzothiadiazole, a substituted or unsubstituted quinoxaline, a substituted or unsubstituted benzobisthiazole, and a substituted or unsubstituted naphthothiadiazole, can be used to tune the electronic band gaps of the polymers for a better light harvesting ability. The disclosed copolymers exhibit field-effect mobilities as high as 0.011 cm2/(V s). Compared to fluorene-containing copolymers with the same acceptor unit, the disclosed ladder-type oligo-p-phenylene containing copolymers have enhanced and bathochromically shifted absorption bands and much better solubility in organic solvents.

Molecular Design and Synthetic Approaches to Electron-Transporting Organic Transistor Semiconductors†

Abstract: This review covers the various classes of molecular structures that may be used as the basis for the synthesis of organic semiconductors that favor electron transport in field-effect transistors and related electronic and optoelectronic devices. The types of compounds include tetracarboxylic diimides, heterocyclic oligomers, fullerenes, and metal complexes. Approaches to polymers are also mentioned. Although brief discussions of transistor operation and applications are included, the emphasis is on the rationale for choosing these structures, and synthetic routes to them. Performance of exemplary compounds in transistors is also discussed.

Synthesis and characterization of a new light-emitting fluorene-thieno[3,2-b]thiophene-based conjugated copolymer

Abstract: A new alternating polyfluorene copolymer, poly(9,9‘-dioctylfluorene-alt-thieno[3,2-b]thiophene) (PFTT), containing a thiophene-condensed thieno[3,2-b]thiophene moiety has been synthesized via a palladium-catalyzed Suzuki coupling reaction. The synthesized polymer was successfully characterized by 1H NMR, 13C NMR, and elemental analysis. It shows good thermal stability and displays unique phase transition behavior between the crystalline and liquid-crystalline states. The ionization potential and electron affinity of PFTT are −5.38 eV and −2.40 eV, respectively, as determined by cyclic voltammetry. Thus, PFTT has an electrochemical band gap of approximately 2.98 eV, which is smaller than that of common polyfluorene (PF) homopolymers. As a film, PFTT exhibits UV−vis and photoluminescence maxima at 471 and 511 nm, respectively. A light-emitting diode device fabricated with an ITO/PEDOT/PFTT/LiF/Al configuration exhibits pure green light emission with the full width at half-maximum (fwhm) of only 57 nm and a ...

Simultaneous Increase in Seebeck Coefficient and Conductivity in a Doped Poly(alkylthiophene) Blend with Defined Density of States

Abstract: The Seebeck coefficient, a defining parameter for thermoelectric materials, depends on the contributions to conductivity of charge carriers at energies away from the Fermi level. Highly conductive materials tend to exhibit conductivity from carriers close to the Fermi level. In this article, we propose polymer blends in which ground state hole carriers, created by doping a minor additive component, are mainly at an orbital energy set below the hole energy of the major component of the blend. Transport, however, is expected to occur through the major component. This leads to a regime in which hole conductivity and Seebeck coefficient may be increased in parallel. While the absolute conductivity of the composite, and thus ZT, are not particularly high, this work demonstrates a route for designing thermoelectric materials in which increases in Seebeck coefficient and conductivity do not cancel each other.

High-photosensitivity p-channel organic phototransistors based on a biphenyl end-capped fused bithiophene oligomer

Abstract: We report highly photosensitive organic phototransistors (OPTs) based on a 2,5-bis-biphenyl-4-yl-thieno[3,2-b]thiophene (BPTT). The measured maximum sensitivity and the ratio of photocurrent to dark current (Iph∕Idark) in BPTT OPTs were 82A∕W and 2.0×105 under 380nm UV light with 1.55mW∕cm2, respectively. The prepared OPTs show a photocurrent response similar to the absorption spectrum of BPTT. The major mechanisms for photocurrent amplification in this device were verified from experimental results as photovoltaic (turn-on) and photocurrent effect (turn-off) by a fitting to theoretic equations.

Synthesis of Conjugated Polymers for Organic Solar Cell Applications

Abstract: -phenylenevinylene)s L4. Fluorene-Based Conjugated Polymers L4.1. Fluorene-Based Copolymers ContainingElectron-Rich MoietiesM4.2. Fluorene-Based Copolymers ContainingElectron-Deficient MoietiesN4.3. Fluorene-Based Copolymers ContainingPhosphorescent ComplexesQ5. Carbazole-Based Conjugated Polymers R5.1. Poly(2,7-carbazole)-Based Polymers R5.2. Indolo[3,2-

Semiconducting π-conjugated systems in field-effect transistors: a material odyssey of organic electronics.

Abstract: Since the discovery of highly conducting polyacetylene by Shirakawa, MacDiarmid, and Heeger in 1977, π-conjugated systems have attracted much attention as futuristic materials for the development and production of the next generation of electronics, that is, organic electronics. Conceptually, organic electronics are quite different from conventional inorganic solid state electronics because the structural versatility of organic semiconductors allows for the incorporation of functionality by molecular design. This versatility leads to a new era in the design of electronic devices. To date, the great number of π-conjugated semiconducting materials that have either been discovered or synthesized generate an exciting library of π-conjugated systems for use in organic electronics. 11 However, some key challenges for further advancement remain: the low mobility and stability of organic semiconductors, the lack of knowledge regarding structure property relationships for understanding the fundamental chemical aspects behind the structural design, and realization of desired properties. Organic field-effect transistors (OFETs) are a kind of device consisting of an organic semiconducting layer, a gate insulator layer, and three terminals (drain, source, and gate electrodes). OFETs are not only essential building blocks for the next generation of cheap and flexible organic circuits, but they also provide an important insight into the charge transport of πconjugated systems. Therefore, they act as strong tools for the exploration of the structure property relationships of πconjugated systems, such as parameters of field-effect mobility (μ, the drift velocity of carriers under unit electric field), current on/off ratio (the ratio of the maximum on-state current to the minimum off-state current), and threshold voltage (the minimum gate voltage that is required to turn on the transistor). 17 Since the discovery of OFETs in the 1980s, they have attracted much attention. Research onOFETs includes the discovery, design, and synthesis of π-conjugated systems for OFETs, device optimization, development of applications in radio frequency identification (RFID) tags, flexible displays, electronic papers, sensors, and so forth. It is beyond the scope of this review to cover all aspects of π-conjugated systems; hence, our focus will be on the performance analysis of π-conjugated systems in OFETs. This should make it possible to extract information regarding the fundamental merit of semiconducting π-conjugated materials and capture what is needed for newmaterials and what is the synthesis orientation of newπ-conjugated systems. In fact, for a new science with many practical applications, the field of organic electronics is progressing extremely rapidly. For example, using “organic field effect transistor” or “organic field effect transistors” as the query keywords to search the Web of Science citation database, it is possible to show the distribution of papers over recent years as shown in Figure 1A. It is very clear

Lanthanide luminescence for functional materials and bio-sciences

Abstract: Recent startling interest for lanthanide luminescence is stimulated by the continuously expanding need for luminescent materials meeting the stringent requirements of telecommunication, lighting, electroluminescent devices, (bio-)analytical sensors and bio-imaging set-ups. This critical review describes the latest developments in (i) the sensitization of near-infrared luminescence, (ii) “soft” luminescent materials (liquid crystals, ionic liquids, ionogels), (iii) electroluminescent materials for organic light emitting diodes, with emphasis on white light generation, and (iv) applications in luminescent bio-sensing and bio-imaging based on time-resolved detection and multiphoton excitation (500 references).

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.

An ultra-lightweight design for imperceptible plastic electronics

Abstract: Electronic devices have advanced from their heavy, bulky origins to become smart, mobile appliances. Nevertheless, they remain rigid, which precludes their intimate integration into everyday life. Flexible, textile and stretchable electronics are emerging research areas and may yield mainstream technologies. Rollable and unbreakable backplanes with amorphous silicon field-effect transistors on steel substrates only 3 μm thick have been demonstrated. On polymer substrates, bending radii of 0.1 mm have been achieved in flexible electronic devices. Concurrently, the need for compliant electronics that can not only be flexed but also conform to three-dimensional shapes has emerged. Approaches include the transfer of ultrathin polyimide layers encapsulating silicon CMOS circuits onto pre-stretched elastomers, the use of conductive elastomers integrated with organic field-effect transistors (OFETs) on polyimide islands, and fabrication of OFETs and gold interconnects on elastic substrates to realize pressure, temperature and optical sensors. Here we present a platform that makes electronics both virtually unbreakable and imperceptible. Fabricated directly on ultrathin (1 μm) polymer foils, our electronic circuits are light (3 g m(-2)) and ultraflexible and conform to their ambient, dynamic environment. Organic transistors with an ultra-dense oxide gate dielectric a few nanometres thick formed at room temperature enable sophisticated large-area electronic foils with unprecedented mechanical and environmental stability: they withstand repeated bending to radii of 5 μm and less, can be crumpled like paper, accommodate stretching up to 230% on prestrained elastomers, and can be operated at high temperatures and in aqueous environments. Because manufacturing costs of organic electronics are potentially low, imperceptible electronic foils may be as common in the future as plastic wrap is today. Applications include matrix-addressed tactile sensor foils for health care and monitoring, thin-film heaters, temperature and infrared sensors, displays, and organic solar cells.