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  • 1
    Electronic Resource
    Electronic Resource
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 86 (1999), S. 4076-4084 
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: Vertical stacking of organic light emitting devices (OLEDs) that emit the three primary colors is shown to be a means for achieving efficient and bright full-color displays. In Paper I, we addressed stacked OLED (SOLED) design and fabrication principles to optimize emission colors, operating voltage, and efficiency. Here, we present results on two different (metal-containing and metal-free cathode) SOLED structures that exhibit performance suitable for many full-color display applications. The operating voltages at 10 mA/cm2 (corresponding to video display brightnesses) are 6.8, 8.5, and 12.1 V for the red (R), green (G), and blue (B) elements of the metal-containing SOLED, respectively. The respective subpixel luminous efficiencies are 0.53, 1.44, and 1.52 cd/A, and the Commission Internationale de L'Éclairage (CIE) chromaticity coordinates are (0.72, 0.28), (0.42, 0.56), and (0.20, 0.22). In the high transparency metal-free SOLED, an insulating layer was inserted between the two upper subpixels to allow for independent grounding of all color emitters in the stack. At operating voltages of 12–14 V, video display brightnesses were achieved with luminous efficiencies of 0.35, 1.36, and 1.05 cd/A for the R, G, and B subpixels, respectively. The respective CIE coordinates for R, G, and B emissions are (0.72, 0.28), (0.26, 0.63), and (0.17, 0.28) in the normal viewing direction, shifting inperceptibly as the viewing angle is increased to as large as 60°. Finally, we discuss addressing schemes of SOLED displays, and compare them with other strategies for achieving full-color, OLED-based displays. © 1999 American Institute of Physics.
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  • 2
    Electronic Resource
    Electronic Resource
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 89 (2001), S. 4986-4992 
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: We study the effects of lithium (Li) incorporation in the cathodes of organic light-emitting devices. A thermally evaporated surface layer of metallic Li is found to diffuse through, and subsequently dope, the electron transporting organic semiconducting thin films immediately below the cathode, forming an Ohmic contact. A diffusion length of ∼700 Å is inferred from analyses of the current–voltage and secondary ion mass spectrometry data. The conductivity of the Li-doped organic films is ∼3×10−5 S/cm. Photoemission spectroscopy suggests that Li lowers the barrier to injection at the organic/cathode interface, introduces gap states in the bulk of the organic semiconductor, and dopes the bulk to facilitate efficient charge transport. © 2001 American Institute of Physics.
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  • 3
    Electronic Resource
    Electronic Resource
    Woodbury, NY : American Institute of Physics (AIP)
    Applied Physics Letters 74 (1999), S. 305-307 
    ISSN: 1077-3118
    Source: AIP Digital Archive
    Topics: Physics
    Notes: We report the demonstration of a transparent, completely metal-free, full-color stacked organic light-emitting device (SOLED). The SOLED emits light from both top and bottom (substrate) surfaces with total external quantum efficiencies of 0.65%, 1.3%, and 2.2% for the green, blue, and red stacked subpixels, respectively. The respective top emission quantum efficiencies for the three subpixels are 0.23%, 0.63%, and 1.6%. The angular dependence of emission colors due to microcavity effects is weak when viewed from the top device surface. This metal-free SOLED is from 21% to 50% transparent over the entire visible spectral range. Capability for top emission makes this device suitable for integration with electronic components in active matrix display backplanes. © 1999 American Institute of Physics.
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  • 4
    Electronic Resource
    Electronic Resource
    Woodbury, NY : American Institute of Physics (AIP)
    Applied Physics Letters 72 (1998), S. 144-146 
    ISSN: 1077-3118
    Source: AIP Digital Archive
    Topics: Physics
    Notes: Lasing at 460, 485, and 510 nm is demonstrated in optically pumped, vacuum-deposited amorphous thin films of a carbazole derivative doped with Coumarin 47, perylene, and Coumarin 30, respectively. Efficient, nonradiative Förster energy transfer between host and dopant organic molecules results in low lasing thresholds (5 μJ/cm2), high differential quantum efficiencies (15%), high peak output powers (20 W), and long operational lifetimes (〉105 pulses at 100 times the threshold power). © 1998 American Institute of Physics.
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  • 5
    Electronic Resource
    Electronic Resource
    Woodbury, NY : American Institute of Physics (AIP)
    Applied Physics Letters 72 (1998), S. 2138-2140 
    ISSN: 1077-3118
    Source: AIP Digital Archive
    Topics: Physics
    Notes: We introduce a class of low-reflectivity, high-transparency, nonmetallic cathodes useful for a wide range of electrically active, transparent organic devices. The metal-free cathode employs a thin film of copper phthalocyanine (CuPc) capped with a film of low-power, radio-frequency sputtered indium tin oxide (ITO). The CuPc prevents damage to the underlying organic layers during the ITO sputtering process. We present a model suggesting that damage-induced states at the cathode/organic film interface are responsible for the electron injection properties of the contact. Due to the low contact reflectivity, a non-antireflection-coated, metal-free transparent organic light-emitting device (MF-TOLED) is demonstrated with 85% transmission in the visible, emitting nearly identical amounts of light in the forward and backscattered directions. The MF-TOLED performance is found to be comparable to that of conventional TOLEDs employing a more reflective and absorptive cathode consisting of a semitransparent thin film of Mg:Ag capped with ITO. © 1998 American Institute of Physics.
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  • 6
    Electronic Resource
    Electronic Resource
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 86 (1999), S. 4067-4075 
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: Vertical stacking of organic light emitting devices (OLEDs) that emit the three primary colors is a means for achieving full-color flat panel displays. The physics, performance, and applications of stacked OLEDs (SOLEDs) are discussed in this and the following paper (Papers I and II, respectively). In Paper I, we analyze optical microcavity effects that can distort the emission colors of SOLEDs if not properly controlled, and describe design principles to minimize these parasitic effects. We also describe the fabrication and operating characteristics of transparent contacts that are an integral part of SOLEDs. We demonstrate that both metal-containing and metal-free transparent electrodes can serve as efficient electron and hole injectors into the stacked organic semiconductor layers. Two different transparent SOLED structures (metal-containing and metal-free) that exhibit sufficient performance for many full-color display applications will be discussed in Paper II. © 1999 American Institute of Physics.
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  • 7
    Electronic Resource
    Electronic Resource
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 62 (1987), S. 2313-2319 
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: A systematic investigation of the effects of antimony dopant on the electronic transport properties of amorphous (GeSe3.5)100−xSbx under high pressure (up to 120 kbar) has been carried out down to liquid-nitrogen temperature for the first time. Differential thermal analysis and x-ray diffraction methods were used for the characterization of freshly prepared and pressure-quenched materials which indicated the presence of structural phase transition in both GeSe3.5 and (GeSe3.5)100−xSbx around 105 kbar pressure. Electrical transport data revealed the strong compositional dependence of the electronic conduction process. A distinct kink in the conductivity temperature plot at pressures〉15 kbar was observed in the Sb-doped compositions indicating the presence of different conduction processes. An attempt has been made to interpret the pressure-induced effect in the transport properties of these glasses considering the possible presence of both thermally activated conduction in the extended states and hopping process in the localized tail states. However, the interpretation of the transport data is not straightforward and the pressure dependence of the thermoelectric power will be needed to complete the picture.
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  • 8
    Electronic Resource
    Electronic Resource
    Woodbury, NY : American Institute of Physics (AIP)
    Applied Physics Letters 74 (1999), S. 1057-1059 
    ISSN: 1077-3118
    Source: AIP Digital Archive
    Topics: Physics
    Notes: Using electro-optical pump and probe measurements, we studied optical properties of a thin film of tris-(8-hydroxyquinoline) aluminum (Alq3) doped with DCM2 laser dye under pulsed injection currents as high as 300 A/cm2. Pump-induced transparency and absorption were observed in the spectral ranges of 570–610 nm and 620–705 nm, respectively. We attribute these optical effects to molecular polarons formed under electrical excitation. Polaron absorption dominates the optical properties of electrically pumped Alq3:DCM2 films in the spectral range where optical gain is anticipated (i.e., from 630 to 700 nm). Polaronic effects may present a significant obstacle for realization of organic diode lasers based on this material system. © 1999 American Institute of Physics.
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  • 9
    Electronic Resource
    Electronic Resource
    Woodbury, NY : American Institute of Physics (AIP)
    Applied Physics Letters 76 (2000), S. 2128-2130 
    ISSN: 1077-3118
    Source: AIP Digital Archive
    Topics: Physics
    Notes: We demonstrate organic light-emitting devices (OLEDs) employing highly transparent cathodes comprised of 2,9-dimethyl-4,7 diphenyl-1,10-phenanthroline (BCP) and an ultrathin film of Li capped with radio-frequency magnetron-sputtered indium–tin–oxide. The cathodes are incorporated onto a conventional bilayer small-molecule OLED. The operating voltages and the total device external quantum efficiencies emitted from the top and substrate surfaces (1.0±0.05)% are comparable to the best conventional undoped OLEDs employing thick metallic cathodes. The device characteristics are independent of the position of Li within the compound cathode, suggesting that Li readily diffuses through BCP to enhance electron injection. An increase of a factor ∼3.5 in the external quantum efficiency is observed compared to devices containing no Li. These results suggest that Li donates electrons to the BCP, increasing its conductivity to the point that band bending occurs to aid in the injection of charge. © 2000 American Institute of Physics.
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  • 10
    Electronic Resource
    Electronic Resource
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 84 (1998), S. 4096-4108 
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: We present a study of optically pumped waveguide and microcavity lasers based on vacuum-deposited thin films of small molecular weight organic semiconductors. Lasing action in waveguide lasers is characterized by high output peak power (50 W), high differential quantum efficiency (70%), low lasing threshold (1 μJ/cm2), and long operational lifetime (〉106 laser pulses at 100 times the threshold pump power). Microcavity laser characteristics include 3 W peak output power, 300 μJ/cm2 lasing threshold, and lifetimes of 〉106 pump laser pulses (operating at 6 times the threshold power). We demonstrate wavelength variability from 460 to 700 nm by changing the composition of the organic films. The confinement of excitations on the dopant molecules leads to quantum dot-like behavior such as high temperature stability of the lasing threshold, output power, and emission wavelength in the temperature range from 0 to 140 °C. The linewidth of laser emission from microcavity structures is found to be 0.2±0.1 Å and is transform limited by 40 ps long relaxation oscillations. We present a theoretical estimate for the linewidth of organic semiconductor laser emission which is found to be at least an order of magnitude smaller than for inorganic laser diodes. The prospects for realizing electrically pumped organic semiconductor lasers are considered. © 1998 American Institute of Physics.
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