Alcohol-Soluble Conjugated Copolymers as Electron Injection/Transporting Materials for PLEDs.

Abstract

In this study, Three kinds alcohol-soluble conjugated polymers, poly[9,9-bis(2-dihexylaminoethoxy)fluorene-co-tetrafluorobenzene] (PFOH-1), poly[9,9-bis(2-dihexylaminoethoxy)fluorene-co-thiophene] (PFOH-2) and poly[9,9-bis(2-dihexylaminoethoxy)fluorene-co-benzo-thiadiazole] (PFOH-3) with different conjugation length and electron affinity were synthesized. These polymers were used as an electron injection/transporting layer of the polymer light-emitting diodes, to modify the electron injection rate from cathode. The devices without using electron injection/transporting materials showed a very poor device performance with a luminescent efficiency (LE) of 0.93 cd/A and a luminance of 248 cd/m2. By using the low work-function metal Ca as cathode, the device showed an almost 2 times increased LE of 2.51 cd/A and brightness of 856 cd/m2, due to greatly enhanced electron injection from cathode. When PFOH-3 was used as the ETL, the device with PFOH-3/Al cathode showed an even similar performance than using Ca as cathode, which exhibited a LE of 2.35 cd/A and a luminance of 667 cd/m2 at the current density of 35mA/cm2.