Device optimization and transient electroluminescence studies of organic light emitting devices
Organic light emitting devices (OLEDs) are among the most promising for flat panel display technologies. They are light, bright, flexible, and cost effective. And while they are emerging in commercial product, their low power efficiency and long-term degradation are still challenging. The aim of this work was to investigate their device physics and improve their performance. Violet and blue OLEDs were studied. The devices were prepared by thermal vapor deposition in high vacuum. The combinatorial method was employed in device preparation. Both continuous wave and transient electroluminescence (EL) were studied. A new efficient and intense UV-violet light emitting device was developed. At a current density of 10 mA/cm2, the optimal radiance R could reach 0.38 mW/cm2, and the quantum efficiency was 1.25%. Using the delayed EL technique, electron mobilities in DPVBi and CBP were determined to be ~10-5 cm2/Vs and ~10 -4cm2/Vs, respectively. Overshoot effects in the transient EL of blue light emitting devices were also observed and studied. This effect was attributed to the charge accumulation at the organic/organic and organic/cathode interfaces.