Highly efficient blue organic light-emitting devices based on improved guest/host combination

We present here a cruciform oligo(phenylenevinlyene) 2,5,2',5'-tetrastyrylbiphenyl (TSB) exhibits excellent properties as host material for blue emitting guest molecule 1,4-di(4'-N,N-diphenylaminostyryl)benzene (DPA-DSB). TSB, which is constructed by linking two rigid distyrylbenzene (DSB) through the phenyl-phenyl bond, shows good optical and electronic properties e.g. high photoluminescent (PL) efficiency and wide band gap similar to DSB. Meanwhile, the central biphenyl core in TSB, which allows the relatively free rotation of two DSB segments along the biphenyl bond, makes it to be conformational multiformity and relatively flexible. As the result, TSB shows the good film forming property and larger loading ability to the guest molecules. The PL efficiencies of guest-host films of DPA-DSB and TSB arrive at the high level around 70% (68% for the 2 wt % DPA-DSB doped film and 72% for the 8 wt % DPA-DSB doped film), which is approaching the PL efficiency of the guest DPA-DSB in dilute solution (78%), indicating that the host TSB can sufficiently disperse the guest DPA-DSB with little aggregation. The organic light-emitting devices using DPA-DSB (2 wt %) doped TSB as blue emitting layer show the maximum efficiency of 12.2 cd/A (6.2%) and 6.39 Im/W, and the maximum brightness of 17350 cd/m(2). Upon further analysis, it has been revealed that the Forster energy transfer and charge trapping are demonstrated to cooperatively work in this doping system.