Effect of the relationship between the energy levels of host and guest on EL performance of phosphorescence organic light-emitting diodes

Abstract

In this work, we used five different fluorescent hosts and six phosphorescent guests to study the effect of the relationship between the energy levels of host and guest on the EL performance of phosphorescence organic light-emitting diodes (PHOLEDs). The experimental results show clearly that the difference between triplet energy levels of the used host and guest plays an important role, and the electron and hole injection barriers, respectively, from electron-transporting layer (ETL) and hole-transporting layer (HTL) into emitting layer (EML) and the mobility of ETL also have a certain influence. It can be seen that the triplet energy level of hosts should be higher than that of guests and the distance between them is as close as possible, ensuring the effective energy transfer from hosts to guests. Furthermore, it is also necessary to have low injection barriers into EML for electrons and holes, and high electron mobility of ETL, which guarantee electrons and holes injected effectively and evenly. This further explains the fundamental reason why the fabrication of high efficiency PHOLEDs must optimize the host, guest and match transporting layers. Our studies will help to establish better design rules for host-guest systems to achieve high performance PHOLEDs. Study the effect of the relationship between the energy levels of hosts and guests and the mobility of ETLs on the EL performance of PHOLEDs. • Study the effect of the relationship between the energy levels of host and guest on the EL performance of PHOLEDs. • The higher T 1 of host than that of guest and the LUMO and HOMO levels of guest within those of host are important. • Low injection barriers and high electron mobility of ETL are effective for carriers to inject and recombine in EML.