The hole mobility of N,N′-bis(naphthalen-1-yl)-N,N′-bis(phenyl)-benzidine (NPB) at various thicknesses (50–1000nm) has been estimated by using space-charge-limited current measurements. A thin layer of buckminsterfullerene has been used for a quasi-Ohmic contact between NPB and indium tin oxide. The mobility at bulk property dominant thickness is in excellent agreement with the results from time-of-flight method. For the typical thickness of organic light-emitting devices, the hole mobility of NPB, 1.63×10−5cm2∕Vs, at 50nm is smaller than the value 7.64×10−4cm2∕Vs at 1000nm (electric field at 0.1MV∕cm). The authors suggest that the lower mobility is caused by the interfacial trap states.

The growth and decay processes of the optically induced birefringence in an azobenzene-functionalized polymer, DR19FPOZ (full name given in the text), and in another azobenzene guest/host polymer system have been studied. The temperature dependence of the birefringence signal is studied, and possible mechanisms associated with the growth and decay segments of the signal are analyzed. Rate constants deduced from the optically induced birefringence signal are also investigated as a function of the laser excitation power and film thickness. The rate constants associated with the growth and decay processes and activation energies are obtained for the polymer system below the glass transition temperature.

We demonstrate that dramatically improved hole injection can be achieved by inserting a very thin C60 film between the indium tin oxide (ITO) electrode and N,N′-diphenyl-N,N′-bis(1,1′-biphenyl)-4,4′-diamine (NPB) layer. This result is ascribed to the formation of an interfacial dipole layer of buckminsterfullerene (C60) on the ITO electrode. The dipole layer induces the surface potential shift that contributes to improve the charge injection efficiency. The chemical shift was downward to help lower the hole injection energy barrier from the ITO electrode to the NPB layer, consistent with the moderately strong electron accepting nature of C60. The enhanced-charge injection provides a simple way of reducing the power consumption of organic electronic devices for real applications.

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The technique of hyper-Rayleigh scattering (HRS) has been employed to investigate the first hyperpolarizability (β) of the azo dye Disperse Red 19 and a polymer in which Disperse Red 19 appears as a side-chain moiety. In addition to HRS, these two molecules were found to exhibit substantial two-photon-induced fluorescence (TPF). The TPF spectra for these molecules were measured, and corrected HRS intensities were obtained. Using an external reference method, β values of (1480 ± 100) × 10-30 and (1470 ± 90) × 10-30 esu were determined for the dye and polymer systems, respectively, in dimethyl sulfoxide at 1064 nm. The difference between these two values is very small and shows that the effect of polymerization on the HRS intensity, in the dilute concentration limit, is negligible.