Angular dependence of the sharply directed emission in organic light emitting diodes with a microcavity structure

An optical microcavity structure was used in organic light emitting diodes. We succeeded in fabricating a device with sharply directed emission vertical to an emission surface. The device shows green emission (bright green) at normal position which turns red (bright red) at the 30degrees position. The angular dependences of the electroluminescence and the emission patterns versus viewing angle in the microcavity OLED were studied. The resonance wavelength lambda decreases with viewing angle. The emission peak at 490 nm is directed vertically to the device surface more sharply than that at 632 nm. The microcavity structure shows non-Lambertian emission. The spectra appear more blue off-axis and the intensity of the green-like emission decreases rapidly with increasing viewing angle. A significantly narrow linewidth of 7.4 nm in the 0degrees direction for the 490 nm peak was observed. The full-widths at half maximum (FWHM) of the green-like spectra are much smaller than those of the red-like ones, indicating better cavity quality.