Ultimate device performances of blue phosphorescent organic light-emitting diodes, an external quantum efficiency of 27.6%, a device lifetime over 10 000 h at 100 cd m−2, and CIE (0.12, 0.13), were achieved by employing an electroplex host.
phosphorescent emitters and stable high triplet energy hosts. [7][8][9][10][11][12] The only lifetime results of the deep blue PhOLEDs was described in the work by Li et al., which tested the lifetime of the deep blue Pt emitters. [10] However, the high efficiency and good lifetime could not be simultaneously achieved in the deep blue PhOLEDs because high triplet energy hosts could not be properly chosen. For example, the deep blue device in Li's work with a y coordinate of 0.18 showed only 800 h lifetime at 100 cd m -2 and low external quantum efficiency of 3.2%. Even the sky blue device with y coordinate of 0.21 exhibited only 9.8% EQE although the lifetime at 100 cd m -2 was about 17 000 h. [10] In order to realize high efficiency and long lifetime at the same time, a stable high triplet energy host as well as a stable deep blue emitter is essential. In general, high triplet energy hosts for deep blue PhOLEDs were either single bipolar hosts such as 3,6-bis(diphenylphosphoryl)-9-phenyl-9H-carbazole, 9-(3-(9H-carbazole-9-yl)phenyl)-3-(dibromophenylphosphoryl)-9H-carbazole or single unipolar hosts such as diphenyl[4-(triphenylsilyl)phenyl]phosphine oxide). [13][14][15][16][17] However, their chemical instability was an issue for application in the lifetime study of the deep blue PhOLEDs. In order to overcome the challenging stability issues of the singlet hosts, mixed hosts of p-type host and n-type host were developed, but lifetime results were not described. [18][19][20][21] Recently, we demonstrated an exciplex host and an electroplex host for extended lifetime in sky blue PhOLEDs. [22,23] Although those two hosts were effective to elongate the lifetime of the sky blue PhOLEDs, intrinsic low triplet energy of each host comprising the exciplex and electroplex hosts limited the application of them in the deep blue PhOLEDs. Therefore, it is necessary to design a high triplet energy host system for deep blue PhOLEDs.In order to develop the high triplet energy host, we focused on the weakly bound exciplex host because the emission energy of the strongly bound exciplex host is largely decreased by strong binding of the p-type and n-type host. The weak binding of the p-type and n-type hosts is advantageous to secure high emission energy for efficient energy transfer to the deep blueemitting phosphorescent emitter. In this work, we developed a high emission energy exciplex host for application in high efficiency and long lifetime deep blue PhOLEDs. Two n-type High triplet energy exciplex hosts are developed using new electron transport type hosts with triphenylsilyl blocking groups to obtain high solid state triplet energy and exciplex triplet energy. Two triphenyltriazine derived hosts, 2-phenyl-4,6-bis(4-(triphenylsilyl)phenyl)-1,3,5-triazine (pSiTrz) and 2-phenyl-4,6-bis(3-(triphenylsilyl)phenyl)-1,3,5-triazine (mSiTrz), are synthesized as the high triplet energy hosts with electron transport properties. The two hosts show high triplet energy over 2.90 eV both in solution and solid film, and afford high triplet e...
A cylindrical single-wall carbon nanotube ͑SWCNT͒ deforms in a nanotube bundle by van der Waals forces. The deformation is hard to measure, but is required in order to understand the properties of bundles. Here, we show that such deformations can be measured from changes in electron diffraction intensities. We demonstrate this for a bundle of two SWCNTs ͑d = 2.05 and 1.56 nm͒. Deformation model predicted by atomistic simulations is scaled to fit the experiment. We show that the best fit gives flattening values of 0.7 and 0.35 Å at the middle of the binding surface for the two SWCNTs.
A general method for quantitative structure analysis of individual, cylindrical, carbon nanotubes is described here. The method is based on electron diffraction of individual nanotubes and analysis using a combination of helical diffraction theory and diffraction geometry of the underlying lattice. Experimental recording of nanotube diffraction is achieved using a nanometer-sized electron beam. Procedures are developed for 1) the measurement of chiral angles in both single- and multi-wall nanotubes and 2) structure determination based on Bessel function fitting of layer line intensity oscillations. The accuracy of the method is demonstrated for the structure determination of a single- and double-wall carbon nanotubes and partial structural analysis of a multiwall carbon nanotube. The results show that the single-, double- and incommensurate multi-wall tubes are well described by the cylindrical tube model. However, a large Debye-Waller factor in the radial direction is obtained. The method developed here is general and can be applied to other cylindrical nanotubes.
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