Efficient deep red phosphorescent OLEDs using 1,2,4-thiadiazole core-based novel bipolar host with low efficiency roll-off

摘要

A series of 1,2,4-thiadiazole core-based bipolar materials,2,2'-(1,2,4-thiadiazole-3,5-diyl)bis(N,N-diphenylaniline) (o-TPATHZ),3,3'-(1,2,4-thiadiazole-3,5-diyl)bis(N,N-diphenylaniline) (m-TPATHZ) and 4,4'-(1,2,4-thiadiazole-3,5-diyl)bis(N,N-diphenylaniline) (p-TPATHZ) were developed as the host matrixes for the deep red phosphorescent emitters tris(1-phenylisoqiunoline)iridium (Ir(piq)3) and [bis(2-methyldibenzo-[f,h]-quinoxaline)Ir(Ⅲ)(acetylacetonate)] (Ir(MDQ)2(acac)).By systematic studying,we demonstrated that there are two types of charge-trapping effect within the emissive layers through adjusting the host-guest compatibility.And,it is revealed that a symmetric charge-trapping effect can contribute to realizing a stable charge-balance,which led to a mitigating efficiency roll-off at high current density.Consequently,a maximum extemal quantum efficiency (EQE) of 16.2％ was achieved by an optimized device with p-TPATHZ-Ir(piq)3 emissive layer.Remarkably,the EQE still remained as high as 15.7％ at the high luminance of 1000 cd/m2.