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)(1)-TPATHZ)were developed as the host matrixes for the deep red phosphorescent emitters tris(1-phenylisoqiuno-line)iridium (It(pie03)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 external quantum efficiency (EQE)of 16.2%was achieved by an optimized device with p-TPATHZ-Ir(piq)3emissive layer.Remarkably,the EQE still remained as high as 15.7%at the high luminance of 1000cd/m^2.