Yeh-Jiun Tung

Blue organic electrophosphorescence using exothermic host–guest energy transfer

We demonstrate efficient blue electrophosphorescence using exothermic energy transfer from a host consisting of N,N′-dicarbazolyl-3,5-benzene (mCP) to the phosphorescent iridium complex iridium(III)bis[(4,6-difluorophenyl)-pyridinato-N,C2′]picolinate (FIrpic). By examining the temperature dependence of the radiative lifetime and the photoluminescence of a film of mCP doped with FIrpic, we confirm the existence of exothermic energy transfer in contrast to the endothermic transfer characteristic of the N,N′-dicarbazolyl-4-4′-biphenyl and FIrpic system. In employing exothermic energy transfer between mCP and FIrpic, a maximum external electroluminescent quantum efficiency of (7.5±0.8)% and a luminous power efficiency of (8.9±0.9)lm/W are obtained, representing a significant increase in performance over previous endothermic blue electrophosphorescent devices.

High operational stability of electrophosphorescent devices

Electrophosphorescent devices with fac-tris(2-phenylpyridine)iridium as the green emitting dopant have been fabricated with a variety of hole and exciton blocking materials. A device with aluminum(III)bis(2-methyl-8-quinolinato)4-phenylphenolate (BAlq) demonstrates an efficiency of 19 cd/A with a projected operational lifetime of 10 000 h, operated at an initial brightness of 500 cd/m2; or 50 000 h normalized to 100 cd/m2. An orange-red electrophosphorescent device with iridium(III) bis(2-phenylquinolyl-N,C2′)acetylacetonate as the dopant emitter and BAlq as the hole blocker demonstrates a maximum efficiency of 17.6 cd/A with a projected operational lifetime of 5000 h at an initial brightness of 300 cd/m2; or 15 000 h normalized to 100 cd/m2. The average voltage increase for both devices is <0.3 mV/h. The device operational lifetime is found to be inversely proportional to the initial brightness, typical of fluorescent organic light emitting devices.

Saturated deep blue organic electrophosphorescence using a fluorine-free emitter

We demonstrate saturated, deep blue organic electrophosphorescence using the facial- and meridianal- isomers of the fluorine-free emitter tris(phenyl-methyl-benzimidazolyl)iridium(III)(f-Ir(pmb)3 and m-Ir(pmb)3, respectively) doped into the wide energy gap host, p-bis(triphenylsilyly)benzene (UGH2). The highest energy electrophosphorescent transition occurs at a wavelength of λ=389nm for the fac- isomer and λ=395nm for the mer- isomer. The emission chromaticity is characterized by Commission Internationale de l’Eclairage coordinates of (x=0.17,y=0.06) for both isomers. Peak quantum and power efficiencies of (2.6±0.3)% and (0.5±0.1)lm∕W and (5.8±0.6)% and (1.7±0.2)lm∕W are obtained using f-Ir(pmb)3 andm-Ir(pmb)3 respectively. This work represents a departure from previously explored, fluorinated blue phosphors, and demonstrates an efficient deep blue/near ultraviolet electrophosphorescent device.

Organic LED Pixel Array on a Dome

We fabricated an array of organic LED (OLED) pixels on a dome of clear polymer foil. The array is first formed on the flat polymer substrate and then is shaped to the dome. During the shaping process, the polymer substrate and the metal interconnect undergo plastic deformation while the OLED pixels remain intact. The OLED pixels have comparable I-V characteristics before and after deformation, but the luminous efficiency was reduced by the deformation, apparently as a consequence of fractures in the aluminum cathode. The demonstration of OLED displays on a spherical surface is an important advance in the fabrication of conformally shaped electronics.

11.1: Invited Paper: Advances in Blue Phosphorescent Organic Light-Emitting Devices

paper discusses the latest developments towards a commercial blue phosphorescent organic light emitting device (PHOLED™) technology. Progress towards achieving a high efficiency, long-lived saturated blue PHOLED is discussed. First, a high efficiency (20% EQE, 45 cd/A), light blue (0.17, 0.39) PHOLED is presented. Next, long-lived blue PHOLEDs having chromaticity co-ordinates (0.17, 0.38) and (0.16, 0.29) are estimated to degrade to half their initial luminance of 200cd/m 2 after >100,000 hrs and 17,500 hrs, respectively. Finally, results from PHOLEDs designed to increase blue color saturation and lifetime are presented. 1. Introductiont organic light emitting devices (PHOLEDs) (1), the singlet excited state (S1) excitons may be converted into the triplet excited state (T1) through inter-system crossing via the presence of a heavy metal atom. In these devices, the triplet states can emit radiatively (T1 to S0), enabling record high conversion efficiencies. The first generation of PHOLEDs contained platinum 2,3,7,8,12,13,17,18-octaethyl-12H,23H-porphyrin (PtOEP) as the dopant phosphor. An impressive external quantum efficiency, at the time, of 6% was reported (2).

Recent progress in high-efficiency phosphorescent OLED technology

A key performance attribute for widespread commercialization of OLED technology is achieving maximum power efficiency along with color chromaticity and operational lifetime. Towards this goal, phosphorescent-OLED (PHOLED) devices have demonstrated potential. Recent PHOLED device results show both excellent device efficiencies and long lifetimes towards the commercialization of low power consumption, full color, passive- and active-matrix (both polysilicon and amorphous-silicon backplane technologies) OLED displays.

49.3: A 200‐dpi Transparent a‐Si TFT Active‐Matrix Phosphorescent OLED Display

We have fabricated a 120×160 high-resolution (200dpi) a-Si TFT active-matrix transparent phosphorescent OLED (PHOLED™) display with novel pixel architecture to maximize transparency and aperture ratio and also ensure comparable light emission from both sides of the display. The a-Si backplane was selected as the technology that would most easily enable the pathway toward achieving high-resolution flexible transparent AMOLEDs (T-AMOLEDs) on polymeric substrates. A-Si TFTs are preferred for fabrication on polymeric substrates since lower process temperatures can be used in comparison to poly-Si TFT processes. As a TOLED generally emits less light from a transparent cathode than anode, a standard 2T pixel was designed with both an opaque, reflective anode region on top of the TFTs as well as a conventional transparent ITO anode to equal the emission from both contacts. This design achieves a total pixel aperture ratio of 64% with a display transparency of 23% in the off-state.

Plastic deformation of a continuous organic light emitting surface

A continuous organic light emitting diode (OLED) surface was shaped by plastic deformation from flat to dome. The OLED dome, now under an average tensile strain of 2.2%, remained operational. This shapeability is achieved by combining a substrate and a device structure that keep functioning in the plastic deformation regime. The technique of conformally shaping a continuous macroelectronic surface could become useful for the manufacture of arbitrarily shaped solid state light sources and mechanical transducers.

52.3: Display Properties of High-efficiency Electrophosphorescent Diodes

The efficiency-vs-current characteristics of phosphorescent organic light emitting diodes (PHOLEDs™) have been studied and compared to fluorescent small molecule organic light emitting diodes (SMOLED) and fluorescent polymer light emitting diodes (PLED). Results show that high efficiency PHOLEDs have significantly higher luminous efficiency than SMOLEDs and PLEDs at both the low and high drive current regimes required for active and passive matrix display applications. The efficiency roll-off of both phosphorescent and fluorescent devices is comparable. Long triplet exciton lifetime and the possible triplet-triplet annihilation do not explain this similarity. Other causes such as polaron-exciton annihilation and electric field induced photoluminescence quenching are provided.

High-efficiency white phosphorescent OLEDs for lighting

Organic light emitting devices (OLEDs) are viewed as a potential next generation lighting source. Phosphorescent OLED (PHOLED) technology, with its inherently high efficiencies, represents the best opportunity to meet the challenging requirements of lighting. We discuss the requirements of OLEDs for lighting applications and present the state-of-the-art of white PHOLEDs, which have demonstrated the luminous efficiencies exceeding 30 cd/A at CIE coordinates of (0.35, 0.33).