A design strategy of exciton blocking materials using simulations and the analysis of device properties

A hole transporting type exciton blocking layer (hEBL) is one of the important device architecture components in phosphorescence organic light emitting diodes (PhOLEDs). In general, hEBL materials with shallow highest occupied molecular orbital (HOMO) energy level result in poor hole transportation in emission layer (EML), leading to unbalanced carrier recombination and an unwanted quenching process. To overcome such issues associated with EMLs, hEBL materials with an appropriate HOMO energy level, good carrier mobility, and sufficient triplet energy are highly required. In this study, we have adopted quantum chemical (QC) and molecular dynamics (MD) simulations to design appropriate hEBL molecules using hole transporting type diphenylamine and carbazole derivatives. By incorporating such hole transporting derivatives into a silica based central core, we have synthesized two hEBL materials, namely 2PCDSi and 2MCDSi. As expected through simulation results, a green PhOLED using 2PCDSi as the hEBL exhibited excellent device performance (an EQE(max) of 31.1%) compared to that using the common reference TCTA material (an EQE(max) of 25.3%) in a similar device structure. Such enhanced properties of synthesized hEBL based devices are supported by their outstanding hole injection, mobility and appropriate triplet energy level. Our current work provides a detailed design strategy of hEBL materials for achieving efficient PhOLEDs.