Solution-processable red phosphorescent OLEDs based on Ir(dmpq)2(acac) doped in small molecules as emitting layer

Abstract

Stable red phosphorescent materials are of high importance in OLED applications and a promising scenario relies on the organometallic emitters, such as phosphorescent dopants, constituting an effective emissive layer of OLEDs, which is usually embedded in an appropriate host matrix. Iridium (III) complexes are the most widely used dopants in Phosphorescent OLEDs because of their high internal quantum efficiency. In this work, Bis(2-(3,5-dimethylphenyl)quinoline-C,N)(acetylacetonato)iridium(III), (Ir(dmpq)2(acac)), was doped in four different small molecule host materials, such as 4,4′-Bis(N-carbazolyl)-1,1′-biphenyl (CBP), 1,3-Bis(N-carbazolyl)benzene (mCP), 1,1-Bis[(di-4-tolylamino) phenyl]cyclohexane (TΑPC) and tris(4-carbazoyl-9-ylphenyl)amine (TCTA), with doping concentrations of 4%, 6%, and 8%. Τhe net host materials and the Ir(dmpq)2(acac) were first characterized in respect of their optical and photophysical properties. Following, the doped thin films were implemented as the active layers in OLED devices, formed via the solution deposition method. It was found that OLED devices fabricated for all studied cases emit red light, a characteristic of Ir(dmpq)2(acac), with a maximum wavelength of approximately 620 nm. By exploring the different combinations between the host and the dopant, as well as the different doping concentrations, we aim to provide insights into the selection of the best performing host materials for PhOLEDs.