Electroluminescent devices based on organic materials are of considerable interest owing to their attractive characteristics and potential applications to flat panel displays. After a brief overview of the device construction and operating principles, a review is presented on recent progress in organic electroluminescent materials and devices. Small molecular materials are described with emphasis on their material issues pertaining to charge transport, color, and luminance efficiencies. The chemical nature of electrode/organic interfaces and its impact on device performance are then discussed. Particular attention is paid to recent advances in interface engineering that is of paramount importance to modify the chemical and electronic structure of the interface. The topics in this report also include recent development on the enhancement of electron transport capability in organic materials by doping and the increase in luminance efficiency by utilizing electrophosphorescent materials. Of particular interest for the subject of this review are device reliability and its relationship with material characteristics and interface structures. Important issues relating to display fabrication and the status of display development are briefly addressed as well.

https://ir.nctu.edu.tw:443/bitstream/11536/28337/1/000179449700001.pdf

Recent progress of molecular organic electroluminescent materials and devices

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Near-Infrared (NIR) Organic Light-Emitting Diodes (OLEDs): Challenges and Opportunities

The basic photophysics, transport properties, state of the art, and challenges in OLED science and technology, and the major developments in structurally integrated OLED-based luminescent chemical and biological sensors are reviewed briefly. The dramatic advances in OLED performance have resulted in devices with projected continuous operating lifetimes of ~2 ? 105?h (~23?yr) at ~150?Cd?m?2 (the typical brightness of a computer monitor or TV). Consequently, commercial products incorporating OLEDs, e.g., cell phones, MP3 players, and, most recently, OLED TVs, are rapidly proliferating.The progress in elucidating the photophysics and transport properties, occurring in tandem with the development of OLEDs, has been no less dramatic. It has resulted in a detailed understanding of the dynamics of trapped and mobile negative and positive polarons (to which the electrons and holes, respectively, relax upon injection), and of singlet and triplet excitons. It has also yielded a detailed understanding of the spin dynamics of polarons and triplet excitons, which affects their overall dynamics significantly.Despite the aforementioned progress, there are outstanding challenges in OLED science and technology, notably in improving the efficiency of the devices and their stability at high brightness (>1000?Cd?m?2).One of the most recent emerging OLED-based technologies is that of structurally integrated photoluminescence-based chemical and biological sensors. This sensor platform, pioneered by the authors, yields uniquely simple and potentially very low-cost sensor (micro)arrays. The second part of this review describes the recent developments in implementing this platform for gas phase oxygen, dissolved oxygen (DO), anthrax lethal factor, and hydrazine sensors, and for a DO, glucose, lactate, and ethanol multianalyte sensor.

https://iopscience.iop.org/article/10.1088/0022-3727/41/13/133001/pdf

Organic light-emitting devices (OLEDs) and OLED-based chemical and biological sensors: an overview

Small molecule and polymer organic light-emitting diodes (OLEDs) show promise of revolutionizing display technologies. Hence, these devices and the materials that render them functional are the focus of intense scientific and technological interest. The archetypical multilayer OLED heterostructure introduces numerous chemical and physical challenges to the development of efficient and robust devices. It is demonstrated here that robust, pinhole-free, conformal, adherent films with covalently interlinked structures are readily formed via self-assembling or spin-coating organosilane-functionalized molecular precursors at the anode−hole transport layer interface. In this manner, molecularly “engineered” hole transport and hydrocarbon anode functionalization layers can be introduced with thicknesses tunable from the angstrom to nanometer scale. These investigations unequivocally show that charge injection and continuity at the anode−hole transport layer interface, hence OLED durability and efficiency, can be ...

Toward the Ideal Organic Light-Emitting Diode. The Versatility and Utility of Interfacial Tailoring by Cross-Linked Siloxane Interlayers

Surface and interface analytical studies have generated critical insight of the fundamental processes at interfaces involving organic semiconductors. I will review surface analytical studies of interface formation of organic semiconductors with different materials. Metal/organic interface is a focus of both device engineering and basic science, since it is a key factor in nearly all important aspects of device performances, including operation voltages, degradation, and efficiency. I will discuss metal–organic interface dipole formation, charge transfer, chemical reaction, energy level alignment, in-diffusion, quenching of luminescence and possible recovery of it. The effect of the insertion of ultra-thin interlayers such as LiF and doping by alkali metals will also be discussed. In organic/organic interface, the energy offset between the two dissimilar organic materials is vitally important to efficient device operation of organic light emitting diodes (OLED), as well as change separation at donor–acceptor interface in organic photovoltaic devices (OPV). I will discuss the interface energy level alignment, band bending, Debye screening, and charge separation dynamics as observed in surface analytical studies, and the implications to OLED and OPV. The interfaces of OSCs with other inorganic materials are also important. For organic thin film transistors (OTFT), the electronic properties of the interface formed between the organic and the dielectric strongly influences the current–voltage characteristics, as the electronic activity has been shown to occur primarily at the interface between the dielectric and the organic materials. I will review the interface formation of OSCs with dielectric materials and with indium-tin-oxide (ITO), a material whose transparency and conductivity make it indispensable for a number of opto-electronic applications and whose electronic properties and energy level alignment with organics have proven dramatically altered by surface treatments.

Surface analytical studies of interfaces in organic semiconductor devices

Organic light-emitting diodes based on tris-8-(hydroxyquinoline) aluminum and N,N‘-diphenyl-N,N‘-(2-naphthyl)-(1,1‘-phenyl)-4,4‘-diamine (NPB) ordinarily have an operating stability of less than 1000 h. Stability and efficiency are, however, dramatically enhanced by interposing a copper phthalocynanine (CuPc) layer between the indium tin oxide (ITO) anode and the NPB hole-transport layer. To specifically understand the origin of an interlayer-induced increase in light output, we have directly measured and analyzed the effective hole injection efficiency from ITO into NPB as a function of the CuPc interlayer thickness. Because NPB is trap free, a direct and self-consistent measure of the hole injection efficiency can be determined from the measured drift mobility and dark current at the same applied field. By this means, we have been able to demonstrate that the hole transport from the ITO anode to the NPB is injection-limited and that the hole injection efficiency is reduced progressively as the CuPc inte...

M. A. Abkowitz

Papers

Tuning the Carrier Injection Efficiency for Organic Light-Emitting Diodes.