Alternating-current polymer light-emitting devices

Abstract

Alternating current polymer light emitting devices (PLEDs) have attracted much attention because ac operation can partially reverse electrochemical reaction at interfaces and a longer lifetime is expected over dc operation. Most ac PLEDs to date are based on symmetrical structure. Here novel alternating current EL devices with asymmetric structure are successfully fabricated by using a hole type polymer PDDOPV [poly (2,5-bis (dodecyloxy)-phenylenevinylene)] and an electron type polymer PPQ [poly (phenyl quinoxaline)]. Two devices with following structure were made, Device 1: ITO/PDDOPV(70nm)/PPQ(40nm)/Al, Device 2: ITO/PDDOPV(100nm)/PPQ(70nm)/Al. Both devices can be operated at forward and reverse dc bias and ac modes but the performance of Device 1 is much better than that of Device 2. Emitting intensity of both devices at forward dc bias was several magnitude orders stronger than that at reverse dc bias. Both the highest luminescent intensity and efficiency of Device 1 at ac operation were the same magnitude order as those at dc operation, but those of Device 2 at ac operation were about 1 magnitude order higher than those at dc operation. Contribution from PPQ increases with the increase of applied voltage.