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Bilayer organic light-emitting diodes based on tris-(8-hydroxyquinolinato) aluminum III have been fabricated where the thickness of the light-emitting layer was varied between 10 and 80 nm while maintaining a constant total thickness of the organic layers. The electroluminescence quantum efficiency of the devices was measured as a function of the emitter thickness, and used to determine the width of the carrier recombination zone at different electric fields. The width of the carrier recombination zone is found to decrease with an increase in electric field [from 70 nm (E=0.75 MV/cm) to 40 nm (E=1.0 MV/cm)]. It is also related to the field-dependent carrier injection efficiency. An estimate of the light output coupling factor (0.4) is also given based on this analysis. © 2003 American Institute of Physics. [ABSTRACT FROM AUTHOR]

Highly oriented indium tin oxide (ITO) thin films were grown by pulsed-laser deposition (PLD) on glass and single-crystal yttria-stabilized zirconia (YSZ) substrates. The structural, electrical, and optical properties of these films were investigated as a function of oxygen partial pressure. Films were deposited at substrate temperature of 300 °C in mixed gases (12 mTorr of argon and 1–50 mTorr of oxygen) using a KrF excimer laser (248 nm and 30 ns full width at half maximum) at a fluence of 1.2 J/cm2. ITO films (300 nm thick), deposited by PLD on YSZ at 300 °C in a gas mixture of 12 mTorr of argon and 6 mTorr of oxygen, exhibit a low electrical resistivity (1.6×10[sup -4] Ω cm) with a high transparency (∼74%) at 550 nm. ITO films deposited on both glass and YSZ substrates have been used as an anode contact in organic light-emitting diodes. A comparison of the device performance for the two substrates shows that the device fabricated on the ITO/YSZ has a higher external quantum efficiency than that of the device fabricated on the ITO glass. [ABSTRACT FROM AUTHOR]

Nonphotochemical hole burning was used to characterize the linear electron–phonon coupling and measure the temperature dependence of the pure electronic dephasing of Al-phthalocyanine tetrasulphonate (APT) in unannealed and annealed hyperquenched glassy films of water (HGW). Below about 10 K, the dephasing is dominated by coupling to the intrinsic two-level systems (TLSint) of HGW. This dephasing is a factor of 5× faster for unannealed HGW due to its higher TLSint number density. For annealed HGW, the pure electronic dephasing time (i.e., that dephasing associated with the zero-phonon line), T2*, is 6.4 ns at 5 K, the slowest dephasing time yet reported for a molecular glassy system at this temperature. At higher temperatures, dephasing due to exchange coupling with pseudolocalized modes at 50 and 180 cm-1, which correlate well with the transverse and longitudinal acoustic modes of water, becomes dominant. The exchange coupling mechanism is based on diagonal quadratic electron–phonon coupling. At 100 K, for example, the pure electronic dephasing times (T2*) are close to 1 ps in value for both types of film. Whereas the transverse acoustic mode is Franck–Condon active (S∼0.5), the 180 cm-1 mode is silent (S<0.02). The determination of the electron–phonon coupling parameters and static inhomogeneous broadening (400 cm-1) of APT’s origin band allowed for simulation of the burn temperature dependence of the overall hole profile (zero-phonon hole plus phonon-sideband holes). Comparison with experimental profiles shows that the hole profile theory of Hayes et al. [J. Phys. Chem. 98, 7337 (1994)] captures the main features of the temperature dependence.The S value of the transverse acoustic mode is used to quantitatively explain the burn temperature dependence of the saturated intensity of the zero-phonon hole and its demise at temperatures just above 100 K (due to Franck–Condon forbiddeness). In view of the... [ABSTRACT FROM AUTHOR]

The effects of deuteration on hole burning of aluminum phthalocyanine tetrasulfonate (APT) in glassy films of water is reported. Deuteration has no effect on the zero phonon hole width of the APT electronic transition, but a large effect on the hole burning kinetics. These effects are discussed in terms of the two level systems of glassy water. © 1996 American Institute of Physics. [ABSTRACT FROM AUTHOR]

Zr-doped ZnO (ZZO) thin films have been investigated as an anode material, a potential alternative to indium tin oxide (ITO), for organic light emitting diode (OLED) devices. ZZO films have been deposited on glass substrates by pulsed laser deposition. The electrical and optical properties of these films were studied as a function of substrate temperature and oxygen pressure during deposition. For a 200-nm-thick ZZO film grown at 250 °C in 1 mTorr of oxygen, a resistivity of 5.6×10[sup -4] Ω cm was measured and an average optical transmittance of 84% was measured in the visible range (400–700 nm). The ZZO films, grown at different oxygen pressures, were used as an anode contact for OLED devices. External electroluminescence quantum efficiencies (0.8%–0.9%) comparable to those (0.9%–1.0%) measured for control devices fabricated on commercial ITO anodes were obtained at high current densities (1000 A/m[sup 2]). These results demonstrate that ZZO is a good anode material. In addition, it is an attractive alternative to ITO due to its low price and lack of toxicity. © 2003 American Institute of Physics. [ABSTRACT FROM AUTHOR]

Films fabricated from commercially available poly(3,4-ethylenedioxythiophene) poly(styrenesulfonate) (PEDOT:PSS) aqueous dispersions have been widely used in many electronic and optoelectronic applications. Previous attempts to utilize them as anodes in organic light-emitting diodes (OLEDs) were not satisfactory due to their low conductivity. In this letter we report on the fabrication and characterization of an OLED device made using a highly conductive form of PEDOT:PSS as anode and demonstrate its superior performance relative to that of a similar device using the commercial conducting polymer as an anode. An external electroluminescence quantum efficiency of ∼0.73% was measured at 100 A/m[sub 2]. [ABSTRACT FROM AUTHOR]