Study On The Application Of Microcavity Effects In Organic Light-emitting Diodes

The high-performance microcavity organic light-emitting diodes(OLEDs) using aluminum as both the semitransparent and reflective electrodes are fabricated, the main research contents include three parts as follows:(1) To obtain the optimal optical and electrical properties of the semitransparent anode simultaneously in bottom-emitting OLEDs, its thickness is necessary to be optimized. The maximum current efficiency is 4.03cd/A when the thickness of semitransparent electrode is 16 nm.The influence of the thickness and refraction index of out-coupling layers on device performances is studied since the luminescence properties can be improved when the out-coupling layer is added on the semitransparent electrode. Alq3 and BCP are chosen as the out-coupling layers. The transmittance of the electrode is increased from 45% to 56% at 530 nm when a 50-nm-thickness BCP is added on the electrode, The optimized microcavity BOLED shows a current efficiency(5.49cd/A) enhancement of 10% compared with a conventional BOLED based on ITO(5.0 cd/A).Slight color variation is observed with increasing angle from 0o to 60 o.(2) In top-emitting OLEDs, the devices are encapsulated using the traditional cover glass method since the top ultrathin Al electrode is rapidly oxidized when exposed to the air. Besides, the transmittance of the top cathode is improved when the out-coupling layer BCP is add on it. The current efficiency is increased by 12%, the maximum value is reached to 6.51cd/A. Due to the weakened microcavity effects intensity, the angle dependence problem has been improved significantly.(3) The modification effect of Mo O3 å'Œ V2O5 as hoe injection layers on the double-Al electrodes inverted OLEDs is studied, the device structure is as follows: glass/ Al/ Li F/ Alq3/ Mo O3 or V2O5/ Al. The results show that V2O5 can improve the anode hole injection more effectively resulting in the decreased turn-on voltage from 4.0V to 3.0V in bottom-emitting inverted OLEDs and from 3.8V to 3.2V in top-emitting inverted OLEDs, the current efficiency is increased from3.7cd/A to 3.85cd/A and from 6.05cd/A to 6.18cd/A respectively.