Efficiency improvement for blue triplet-triplet annihilation upconversion organic light-emitting diode

Recently, a new emission mode, triplet-triplet annihilation up conversion (TTAUC), of OLED was proposed with the mechanism as follows: when the carriers recombine at the sensitizer layer with a lower energy bandgap, the generated triplet excitons of sensitizer transfer to the triplet-triplet annihilation (TTA) emitter and emit a higher energy photon. In our experiment, we used tris(8-hydroxyquinolinato)aluminum (Alq3) as sensitizer, 9,10-Bis(2-naphthyl)anthraces (ADN) as TTA emitter and 1,1'-(2,5-Dimethyl-1,4-phenylene)dipyrene (DMPPP) as triplet diffusion singlet blocking (TDSB) layer. To improve the efficiency of TTAUC-OLED, 4,4’ -Bis[4-(di-p-tolylamino)styryl]biphenyl (DPAVBi), was doped in ADN host. With 6% of DPAVBi doping, no obvious change was observed in electrical characteristics, indicating electron traps from dopant is limited. Maximum EQE achieved EQE= 4.66% in the optimized device.