Highly efficient hot exciton deep-blue OLEDs based on triphenyl-phosphine oxide modified anthracene derivatives

Abstract

The utilization of triplet state excitons is important for the efficiency of organic light-emitting diodes (OLEDs). In this work, two isomers (p-PIAnPO and m-PIAnPO) of anthracene-based derivatives with triphenylphosphine oxide (PO) and phenanthroimidazole (PI) in different positions were designed and synthesized. In particular, PO provides large spatial hindrance and promotes hole transport, and PI has excellent bipolar transport ability, which helps to balance carrier transport. The para-linkage (p-PIAnPO) favors conjugation expansion and achieves high luminescence efficiencies, whereas the meta-linkage (m-PIAnPO) provides a highly twisted molecular conformation, thus effectively interrupting conjugation and leading to deep-blue emission. These molecules exhibit excellent thermal stability and efficient electroluminescence properties. Non-doped OLEDs using p-PIAnPO and m-PIAnPO as the light-emitting layers achieve maximum external quantum efficiencies of 6.0% and 4.2% with the λEL at 466 nm and 448 nm, corresponding to high exciton utilization efficiency (EUE) of 59%–88% and 54%–81%. In addition, p-PIAnPO-based OLEDs achieve an ultra-low efficiency roll-off of 1.7% at 1000 cd m−2. Theoretical calculations and experimental results show that the high EUE is mainly attributed to the high-lying reverse intersystem crossing from T3 to S1 namely hot exciton channel.