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Using organic light-emitting diodes (OLEDs) without encapsulation, dark spot growth and its acceleration factor at high temperature and high humidity were measured and compared with those of edge shrink at the cathode edge. The water permeation model explained the time evolution of dark spots and edge shrink, and the acceleration factor was the same between dark spots and edge shrink. The acceleration factor of edge shrink was proportional to the relative humidity at a constant temperature and showed Arrhenius temperature dependence.

Efficient light extraction is a critical issue for improving the overall efficiency of organic light-emitting diodes (OLEDs). Improvements in OLED efficiency are studied via the introduction of photonic crystal (PC) layers, which are expected to enable versatile control of photons. We fabricate two-dimensional PC structures in organic and electrode layers, in which most light is confined, to extract the light in the waveguide mode. Improvements in OLED efficiency of 20 and 130% are observed in spectrally integrated intensity and the peak intensity of forward-propagating light, respectively, in comparison with samples without PCs. As the thickness of the organic layer is partially reduced, lower operating voltages are found not to degrade light-extraction efficiency. We can expect further improvement in the overall OLED efficiency by optimizing PC structure.

Multilayer organic light-emitting devices with phosphorescent guest emitter, tris(2-phenylpyridine) iridium doped in a host 4,4′-N,N′-dicarbazol-biphenyl layer were prepared. The device with the 6.5 wt% guest emitter exhibited external quantum efficiency and power luminous efficiency of 13.7% and 38.3 lm/W, respectively at the luminance of 105 cd/m2 driven at the voltage of 4.0 V and current density of 0.215 mA/cm2. The half decay lifetime under continuous constant-current driving for the initial luminance of 500 cd/m2 was 170 h.

To understand the low lying excited states of trans-polyacetylene, optical properties were studied at room temperature on carefully prepared samples by measuring photocurrent (PC) and photovoltage excitation spectra as well as optical absorption and reflectance. The 1.4 eV PC peak, the appearance of which sensitively depends on the sample quality, is correlated with some additional absorption sticking to the intrinsic absorption edge. An enhancement of PC with Au-Al electrodes biased reversely was observed in excitation spectra between 1.5∼2.0 eV, indicating that the formation of excitons causes three reflection peaks in this spectral region.

Polyacetylene film with aligned fibrils across the film thickness was synthesized using a liquid crystalline catalyst under a magnetic field. The morphology observed by an electron microscope was characteristic in the fibril thickness (no less than 1 µm in diameter) in addition to the fibril orientation. The presence of well developed fibrils across the film thickness suggests the possibility of intrafibrillar electric measurements.