White organic light-emitting diodes (WOLEDs) resemble light more naturally, with emission spectrum that is comfortable to the human eye. A lot of effort has been devoted to improve the performance of WOLEDs. This research work was aimed at studying the emission behavior of WOLEDs, improving the device performance, and thereby developing several novel device concepts for application in high performing transparent WOLEDs and organic proximity sensors. Emission behavior, in terms of color stability and injection characteristics of phosphorescent organic light-emitting diodes (OLEDs), was investigated systematically and optimized via the experimental optimization and optical simulation. The transparent WOLEDs can be almost invisible at daytime and can emit a pleasant diffused light at night, allowing the surface light source to shine in both directions. It is an exciting new lighting technology that could bring new device concepts. However, undesirable angular-dependent emission and asymmetrical emission characteristics are often observed in transparent WOLEDs. In this work, a pair of optically and electrically comparable transparent anode and cathode was introduced to form weak microcavity transparent WOLEDs, e.g., employing a pair of Ag (10 nm)/MoO3 (2.5 nm)-modified indium tin oxide anode and Al (1.5 nm)/Ag (15 nm)/NPB (50 nm) cathode. It is found that the avoidance of the spectral overlap between the peak wavelengths of the emitters and the resonant wavelength of the organic microcavity moderates the angular-dependent electroluminescence emission behavior, thereby improving the color stability of the transparent white WOLEDs over a broad range of the viewing angles. As a result, the transparent WOLEDs developed possess a visible-light transparency of >50%, a symmetrical bi-directional illumination with an almost identical power efficiency of 11 lm/W (measured at 100 cd/m2) and the similar CIE coordinates of (0.36, 0.43) and (0.38, 0.46) measured from both sides of the devices. Efficient charge injection is a prerequisite for achieving low turn-on voltage and improved hole-electron current balance in OLEDs. Metal oxide (e.g. MoO3) is a commonly used hole-injection layer (HIL) for reducing the energy barrier at the anode/organic interface for efficient charge injection. However, fluctuation in the quality of the metal oxide-based HIL, e.g., changes due to the MoO3 formulation, film fabrication and post-treatment conditions, often places a practical challenge limiting reproducibility of the device performance. In this work, an effective solution-processed HIL that consists of a mixture of PEDOT:PSS and MoO3 was developed for application in OLEDs. It is found that the presence of the solution-processed HIL at the interface between the anode and the organic improves the hole injection and the performance reproducibility of the phosphorescent OLEDs. The effect of the presence of the MoO3 in the solution-processed HIL on charge injection in phosphorescent OLEDs, with a configuration of glass/ITO/CBP/ CBP:Ir(ppy)2acac/TmPyPB/LiF(1.0 nm)/Al(70 nm), was examined. It is shown that solution-processed HIL has a superior hole injection characteristic at the HIL/hole transporting layer (HTL) interface compared to that in the devices fabricated with a pristine PEDOT:PSS or a pure MoO3 HIL, yielded phosphorescent OLEDs with an external quantum efficiency of ~25% and a power efficiency of ~75 lm/W @ 1000 cd/m2. The morphological and surface electronic properties of the hybrid HIL were also investigated by AFM, XPS and UPS measurements, revealing the formation of a good contact at the HIL/HTL interface in the phosphorescent OLEDs. Apart from improving the device performance, a new organic proximity sensor based on the monolithic integration of organic photo-detectors (OPDs) and OLEDs was also developed. A MoO3-modified thin silver interlayer, serving simultaneously as a transparent cathode for the OPDs and an anode for the OLEDs, is used to link the functional organic electronic components. In the integrated OLED/OPD-based proximity sensors, the OLED components function as an illumination source while the coupled OPD units enable a high absorption when light is reflected from objects to create an optical signal. The photosensitivity is enhanced using organic photosensitive bulk heterojunction in the OPDs, thereby realizing a high photosensitivity and the high external quantum yield at a low reverse bias. The signal to noise ratio, optical and frequency responses of the integrated organic proximity sensors were optimized and examined. The design and fabrication flexibility of the integrated OLED/OPD-based organic proximity sensors also have cost benefits, making it possible for application in wearable units and compact information systems.

No description available.

No description available.

We have developed high-efficiency blue organic light-emitting devices incorporate 1,3,5-Tri(1-pyrenyl)benzene(TPB3) as emitting layer and 4,7-diphenyl-1,10-phenanthroline(BPhen) as the electron transporting layer, which has a large Highest Occupied Molecular Orbital energy level and has good electron mobility. A device having the configuration : ITO(140 nm)/NPB(65 nm)/(TPB3 40nm)/BPhen(30 nm)/LiF(0.8 nm)/Al(200 nm) exhibited a maximum luminance at 9.5V of 29940 cd/m2, The maximum current and power efficiencies were 3.85 cd/A and 2.38 lm/W, respectively. The current and power efficiencies were greater than 3cd/A and 1.1 lm/W respectively, Over a large range of potentials (3.5~10.0V) with good Commission Internationale de l¡¦Eclairage (CIE) coordinates of (0.17, 0.22). These results indicate that TPB3 is good blue-emitting material for OLED applications. The photophysical and chemical properties of TPB3 have also been studied in this research.

ABSTRACT Organic light emitting diode (OLED) has significant scientific implication and technological potential. Using organic materials for tailored emitting color, threshold voltage reduction, and emission efficiency gain are the key points for the commercialization of OLED. An UV-Vis spectrophotometer was applied to obtain the absorption spectra of PVK, C6, and PRL, as well as their respective band gap (Eg) values of 3.49 eV, 2.32 eV, and 2.55 eV. The turn-on oxidation potential of cyclic voltammograms was reduced for HOMO energy at 5.64 eV, 5.21 eV, and 5.16 eV, respectively. The Eg subtracted from HOMO energy yielded the respective LUMO values of 2.15 eV, 2.89 eV and 2.61 eV. Excitation at 457 nm or 325 nm was applied to the freestanding films of PVK, PVK doped with C6 (10/1), and PVK doped with PRL (10/1). From the UV-Vis absorption spectra and Egs, we knew that 457 nm excitation did not generate photoluminescence (PL) of PVK. The PL spectra of the doped freestanding films were mostly attributed to the dye molecules of C6 or PRL. The PL spectra of doped freestanding films were insensitive to the excitation sources at 325 nm and 457 nm. There was a blue shift at the PL emission peak indicative of energy transfer from PVK to C6 or PRL for the doped films. Using spin-coating or vacuum deposition to fabricate PVK, C6, and PRL films onto an ITO substrate followed by evaporating Al (Ag) as the electron injector to form OLED devices. Because of the energy transfer between PVK and C6 or PRL, ITO/PVK:C6/Al homojunction OLED showed a smaller threshold voltage than that of ITO/C6/Al, from 9 V to 3.5 V. Likewise, ITO/PVK:PRL/Al homojunction OLED had a smaller threshold voltage than that of ITO/PRL/Al, from 8 V to 4.5 V. PVK was also used as the hole blocking layer to construct heterojunction OLED to balance electron-hole numbers in the emitting layer. The threshold voltage of ITO/C6/Al reduced from 9 V to 7 V with a heterojunction of ITO/PVK/C6/Al. A device of ITO/PRL/Al having a threshold voltage of 8V reduced to 6V with an ITO/PVK/PRL/Al heterojunction OLED. Coating a protective layer (Ag) on the metallic electron injector, or packaging the device in N2 could both decrease the decay and increase the life time of OLED.

Developing organic light-emitting diodes (OLEDs) as the next generation display devices is not only of industrial interest, but also a scientific challenge in and of itself that requires multi-disciplinary efforts to make the technology successful. Thermally activated delayed fluorescence (TADF) is a recent breakthrough in OLED technology whose prime value is to enable purely organic emitters to recruit the dark triplet excitons in the device, thus avoiding expensive and toxic rare metal based emitters. This thesis is centred on TADF and contains work in three major areas. Firstly, novel ionic TADF emitters were designed for use in light-emitting electrochemical cells (LEECs), which is an alternative electroluminescent device technology to OLEDs, with a much simplified fabrication procedure and architecture. The vast majority of these ionic emitters are based on reported TADF scaffolds where the donors were tethered with an imidazolium hexafluorophosphate group to obtain the ionic character required for LEEC devices (TL and BTL series, Chapter 2). On the other hand, TADF emitters with a carboxylate group were also designed which act as both acceptor and intrinsic charged functionality for LEEC applications (CTL series, Chapter 2). Secondly, attempts were made to create novel TADF molecular scaffolds in order to enrich the current library of TADF emitters. Research efforts were focused on polyaromatic moieties such as anthracene (An series, Chapter 4) and fluoranthene (FA series, Chapter 4) that are seldom reported in TADF literature. In addition, TADF emitters with phosphine oxide as the acceptor group have also been studied (PO series, Chapter 5). Lastly, structure-property relationship studies of TADF emitters were undertaken as a function of tuning of donor and acceptor functionalities using both theoretical and experimental approaches in order to gain more insight for designing desirable TADF emitters (Chapter 3).

No description available.

No description available.

No description available.

In the past decades, polymeric light-emitting diode (PLED) have been a focus of research interest to scientists all over the world due to its potential application in flat panel displays. In previous studies, tremendous progresses in material developments, device engineering and theoretical modeling for PLEDs have been achieved. However, there are still a number of crucial problems to be solved in order for PLEDs to be widely employed in commercial flat panel displays. In this thesis, we present studies of PLEDs that used a high work-function metal aluminum as the cathode. The device exhibits a highly enhanced efficiency by modifying the cathode using certain non-ionic surfactant polymers. Based on this finding, we further demonstrated top-emitting PLEDs with environmentally stable cathodes. In another development, we show that a three-coloremitting device with a bilayer emitting polymer structure can be achieved by a dry photo-patterning process. Each of the red, green and blue emission in the device has a comparable emitting efficiency to the traditional standard red, green or blue device with single color emission. These results are believed to be important and beneficial for obtaining low-cost, large-scale and long life-time flat panel displays based on PLEDs. / by Deng Xianyu. / "September 2006." / Adviser: King Young Wong. / Source: Dissertation Abstracts International, Volume: 68-03, Section: B, page: 1871. / Thesis (Ph.D.)--Chinese University of Hong Kong, 2006. / Includes bibliographical references (p. 92-101). / Electronic reproduction. Hong Kong : Chinese University of Hong Kong, [2012] System requirements: Adobe Acrobat Reader. Available via World Wide Web. / Electronic reproduction. [Ann Arbor, MI] : ProQuest Information and Learning, [200-] System requirements: Adobe Acrobat Reader. Available via World Wide Web. / Abstracts in English and Chinese. / School code: 1307.