Highly efficient deep-blue fluorescence OLEDs with excellent charge balance based on phenanthro[9,10-d]oxazole-anthracene derivatives

Abstract

Two blue fluorescent materials, m-PO-ABN and p-PO-ABN, are newly synthesized by controlling the conjugation length based on different linkages of the meta or para position between the phenanthro[9,10-d]oxazole (PO) moiety and anthracene substituted with a cyano group. The two materials emit deep-blue light with a high photoluminescence quantum yield (PLQY) in solution state. Non-doped devices fabricated using m-PO-ABN and p-PO-ABN show the EL peaks at 448 and 460 nm corresponding to the Commission Internationale de L’Eclairage (CIE) coordinates of (0.148, 0.099) and (0.150, 0.164), respectively. The external quantum efficiency (EQE) values of the devices are 5.9% and 5.3% for m-PO-ABN and p-PO-ABN, respectively. Transient EL measurements and optical calculation results reveal that both materials exhibit good charge balance and triplet–triplet annihilation in the devices, which may originate from enhanced bipolar characteristics due to the insertion of PO and cyano moieties.