Green and Red Electrophosphorescent Devices Consisting of Cabazole/Triarylamine-Based Polymers Doped with Iridium Complexes

Abstract

Two types of polymers were synthesized such as poly[N-(2-ethylhexyl)carbazole-alt-N-(4-aminophenyl)carbazole] (PECAC) and poly[N-(2-ethylhexyloxy-phenyl) carbazole-alt-N-(4-aminophenyl)carbazole] (PEPCAC). These polymers are designed to have carbazole groups with wide band gap and a triarylamine moiety with a hole transporting property. Green and red phosphorescent polymer light emitting diodes (PhPLEDs) were fabricated with an emitting layer consisting of either PECAC or PEPCAC as a host matrix with suitable iridium complexed, Ir(ppy)₃ as a green or IR-PIQCH as a red dopant, respectively. Red PhPLEDs doped with IR-PIQCH exhibited maximum EL emission peaks at 620 nm with higher luminescence and lower driving voltage, due to effective energy transfer from host polymers to IR-PIQCH red dopant. Based on HOMO and LUMO levels of the polymers and Ir(ppy)₃, however, the synthesized polymers could not be served as suitable host polymers for Ir(ppy)₃ green dopant. Ir(ppy)₃ doped PhPLEDs exhibited red shift and wide range of EL emission.

Keywords:

• carbazole
• dopant
• host
• phosphorescence
• PLED
• triarylamine

Acknowledgments

This work was supported by Daegu University Research Grant 2006.

Notes

^a Temperature resulting in 5% weight loss based on initial weight.

^a Calculated from the crosspoint of UV-Vis and PL spectrum.

^b Measured by a RIKENKeiki AC-2.

^c Estimated from the HOMO and band gap.