Characterization of properties of polymeric light-emitting diodes over extended periods

Abstract Light-emitting diodes fabricated with a layer of poly( p -phenylenevinylene) (PPV) sandwiched between electrodes of indium-tin oxide (ITO) and calcium have been studied over extended periods of operation. Different biasing conditions, with drive at constant voltage, constant current and with a.c. voltage have been used. The best results indicate that continuous operation with square-wave biasing (50% duty cycle, 1070 Hz) and current density in the range 300–800 mA/cm 2 can be achieved beyond 1200 h. This amounts to about 825 A h/cm 2 total charge flux through the device. No significant spectral aging has been detected on this time scale. Emission spectra do not change even when varying the frequency of sinusoidal excitation or the level of a d.c. bias.

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