Abstract We demonstrated high‐brightness large‐area, white organic light‐emitting diode (OLED) consisting of printing‐processed organic semiconductor layers. Meniscus printing process was applied to the substrate with 2 μm‐high stripe‐shape auxiliary electrodes. The OLED panel showed white emission all over the whole emitting area of 58 mm × 52 mm, high average luminance of 10,000 cd/m 2 , luminance uniformity of 40 %, and high luminous flux of 95 lm.
A theoretical equation has been fitted to time-of-flight photocurrent transients of molecularly doped polymers in order to obtain the diffusion coefficient (D) and drift mobility (\ensuremath{\mu}) simultaneously. D and \ensuremath{\mu} did not show the sample thickness dependence such as was previously reported. The logarithm of D and \ensuremath{\mu} increased linearly with the square root of the electric field and decreased linearly with ${\mathit{T}}^{\mathrm{\ensuremath{-}}2}$. The negative field dependence of the mobility in low electric field, obtained from the intersection time of asymptotes of the plateau and the trailing edge of the photocurrent transients, can be interpreted to be a result of the combination of drift and diffusion. \textcopyright{} 1996 The American Physical Society.
Hole mobilities have been measured in diethylamino-benzaldehyde-diphenylhydrazone (DEH)-doped polymers as a function of the polymer composition, temperature, and electric field. It was found that the electric field dependence on the mobility was a strong function of the binder polymer employed. In all cases, the electric field dependence E can be described as exp(βE1/2T−1). β2 is related to the density of photoinduced spins in the molecularly doped polymers, which are related to the interaction between DEH and the polymer.
A transport equation has been fitted to time-of-flight transient photocurrent signals of molecularly doped polymers in order to obtain both diffusion coefficient (D) and drift mobility ((mu) ) simultaneously. The logarithm of (mu) increased linearly with the square root of the electric field. The negative field dependence on the square root of the electric field at a low electric field that had been reported appeared to superimposing of drift and diffusion. The logarithm of D increased linearly with the square root of the electric field. The logarithm of D decreased linearly with T-2.
The efficiency of carrier generation by the zerographic discharge technique has been measured on four films; a molecularly C60-doped polymer film, a molecularly C70-doped polymer film, an aggregate C60 film, and an aggregate C70 film. The yield for molecularly C70-doped polymer was three orders of magnitude larger than that for the film of molecularly C60-doped polymer. The photon energy dependence of efficiency for the aggregate films differed from that for the molecularly doped polymer films. The carrier generation efficiency spectrum for the aggregate films showed peaks corresponding to the Frenkel type excitons. The sensitivity of a photoreceptor fabricated with C70 was 0.5(cm2/(mu) J) at wavelengths in the 420nm-670nm region.
A theoretical photocurrent transient equation for a thin or thick sample was derived from the charge transport equation. This equation has been fitted to measured photocurrent transients of molecularly doped polymers in order to obtain the actual relationship between the mobility (µ) and the diffusion coefficient (D). The relationship between the mobility and the diffusion coefficient has been derived from the Langevin equation which takes into account the random electric field resulting from the randomly located and the randomly oriented electric dipoles. A time correlation function of the fluctuating electric field necessary for calculating the diffusion coefficient is assumed to be 2σE2exp (-|t|/τ), where σE is the dispersion of the fluctuating electric field, which is proportional to the electric dipole moment, and τ is the correlation time of the electric field fluctuation. The result, D=τσE2 µ2, was consistent with the actual relation, D∝µ2.
Drift mobilities and diffusion coefficients of molecularly doped polymers, with dipole moment as a parameter, have been measured by fitting a theoretical equation to time-of-flight photocurrent transients. The slope of the logarithm of mobility vs the square root of electric field is proportional to the dipole moment squared. A similar relationship is observed for diffusion coefficients. We analyze the results using disorder formalism and estimate the dipolar contribution ${\ensuremath{\sigma}}_{d}$ to the width of the density of states. The constant of proportionality in the relation between ${\ensuremath{\sigma}}_{d}$ and the dipole moment squared coincides with the theoretical value given by the dipole trap model. This result provides an important demonstration of the validity of both the disorder formalism and the dipole trap model.
Abstract Irradiation of fluorescent light onto a solid solution containing a hydrazone compound and a polymer generated stable polymer radicals at room temperature. Spin concentration was 1013 spins/g and saturated within 6 h under 10 Klx fluorescent light. The factors affecting the stable radical formation are discussed.
The charge carrier trapping property of a guest-host system was investigated. The molecularly doped polymer (MDP) consisted of poly(N-vinyl carbazole), plasticizers, a nonlinear optical material, and a trapping molecule. The trapping molecules used were a carbazole dimer and a well-known charge transporting material, 4-(diethylamino)benzaldehyde diphenylhydrazone (DEH). The response time of a MDP doped with the carbazole dimer was faster than that of the MDP doped with DEH, whereas their lifetimes were almost the same. Semi-empirical molecular orbital calculations were carried out for these two trapping molecules and show that the carbazole dimer suffered a larger change in the molecular geometry when it was ionized. A longer lifetime and faster response time are expected by optimizing changes in molecular geometry.
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