2,7-Difluo-carbazole and 2,4,5,7-tetrafluoro-carbazole were synthesized as new building blocks of wide-energy-gap host material for phosphorescent organic light-emitting diodes (PHOLEDs). These fluorinated positions in the carbazole ring were determined on the basis of density functional theory calculation results. Spectroscopic analyses supported the hypothesis that poly(Nvinyl-2,7-difluoro-carbazole) (2,7-F-PVK) with the fluorinated pendant group possessed a wide energy gap, leading to the exciton energy confinement on the blue phosphorescent dopant as well as nonsubstituted poly(N-vinyl-carbazole) (PVK). 2,7-F-PVK was used in solution-processed blue PHOLED to achieve 27 cd/A at 760 cd/m 2 , which is 1.8 times higher than that of nonsubstituted PVK. We assumed that the replacement of nonsubstituted PVK with 2,7-F-PVK improved the charge balance in the emission layer, while keeping the exciton confinement effect. The fluorination of the carbazole ring is a useful molecular design strategy for wide-energy-gap host material.
A new concept of an effective mass in the slowing down of fast neutrons is introduced. This concept, by accounting for absorption in an increased effective mass, places scattering in the presence of absorption on a formally equivalent basis with pure scattering. Thus absorption in slowing-down theory need not be considered as a separate phenomenon, but only as a generalized form of pure scattering.For a mixture, the effective mass includes the effect of absorption in an effective single element. A model of the moderation process is considered which allows a description of the mixture by the simpler single-element equations.
A 70 mm x 80 mm OLED lighting panel with efficacy of 78.6 lm/W at 1000 cd/m has been demonstrated. We improved the efficacy of the panel by decreasing driving voltage. We adopted two approaches: optimize device structure by using high-mobility electron transport layers and improve luminous uniformity by embedding metal bus lines. 2
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