A deep blue fluorescent emitter functioning as host material in highly efficient phosphorescent and hybrid white organic light-emitting devices

A deep blue fluorescent emitter of 4', 4'''-(1H-phenanthro [9, 10-d]-imidazole-1, 2-diyl) bis (N, N-diphenyl-[1,1'-biphenyl]-4-amine) (PPI-2TPA) possessing special virtues of high triplet energy, excellent photoluminescence quantum yield and preferable bipolar transporting property was employed as host material by the first time to realize a highly efficient phosphorescent organic light-emitting device (OLED). In comparison with the reference device, the optimized device had better performance, which showed the maximum efficiencies of 40.4 cd/A and 45.3 l m/W and still kept high efficiencies of 39.7 cd/A and 37.1 l m/W at the luminance of 1000 cd/m(2). Moreover, the critical current density was as high as 179.6 mA/cm(2), which was about 1.8-fold that of the reference device, indicating a significant alleviation of efficiency drop at high current density in the optimized device. The emission of phosphorescent emitter originated from both energy transfer and hole-electron recombination, distinctly revealed by a systematical analysis on the device electroluminescence (EL) characteristics. Simultaneously, an efficient hybrid white OLED as well as a tandem white OLED which demonstrated quite slight color variation over a wide range of luminance were also constructed.