Synthesis and characterization of bipolar host materials based on indolocarbazole derivatives for green phosphorescent organic light-emitting diodes

Abstract

In this study, new host materials were developed to enhance the limited bipolar characteristics of the thermally stable indolocarbazole (ICz) moiety by incorporating phenylcarbazole (PCz), an electron donor, and dibenzothiophene (DBT), an electron acceptor, which has distinct carrier transport properties. The newly synthesized hosts, ICz-PCz and ICz-DBT, exhibited excellent thermal stability, with T₅% values of 370 °C and 371 °C, respectively, and triplet energies of 2.86 eV and 2.87 eV. Therefore, these hosts are suitable for use in green phosphorescent OLEDs (PhOLEDs). Additionally, electrochemical and single-carrier device analyses revealed that the substitution of DBT improved electron transport properties compared with PCz. The enhanced electron mobility of DBT, attributed to its acceptor characteristics, was validated through single-carrier device measurements, demonstrating superior performance over PCz. Consequently, PhOLEDs using ICz-DBT achieved a notable external quantum efficiency (EQE) of 23.15 %, underscoring the effectiveness of our strategy to synthesize thermally stable bipolar host materials. The proposed solutions overcome thermal stability issues that could improve OLED performance, longer device lifespans, and expanded applications in harsh environments.