In order to understand the characteristics of ohmic hole-contacts for the inverted/conventional organic light emitting devices, a hole-only device with all ohmic contacts, which is composed of glass/ITO/MoOx/4,4,4-tris[2-naphthyl-phenyl-amino]triphenylamine (2-TNATA)/MoOx/Al, the elements of the electronic structures of MoOx-on-2-TNATA interface and 2-TNATA-on-MoOx interface were investigated by photoemission spectroscopy, with regards to interface energetics, formative mechanism, and a potential charge carrier injection. The electronic structures revealed that the behavior of the interface between MoOx and 2-TNATA was different whether MoOx was deposited on (2-TNATA) or vice versa. The bottom interfaces of 2-TNATA-on-MoOx in this hole-only devices showed no hole-injecting barrier height (Phi(h)B) when the thickness of 2-TNATA was deposited in the range of 0.1 to 5.0 nm on the 10.0 nm-thick MoOx thin films. This has been explained to be attributed to both metal-induced gap states and a chemical reaction at the interfaces. The top interfaces of MoOx-on-2-TNATA in this hole-only device structure also showed no Phi(h)B when a hole was injected from the MoOx-on-2-TNATA interfaces to cathode. The hole-ohmic property in the top interfaces depends on interface dipole by the formation of charge transfer complexes as well as interdiffusion of MoOx into the 2-TNATA film in these interfaces.
This study aimed to synthesize novel hole transporting materials (HTMs) with biphenyl derivatives that are di- or tetra-substituted with naphthylphenyl amine groups and/or methoxy groups, and to examine systematically the variations of the properties of the HTMs with the number and location of the substituents. The tetranaphthylphenyl amine-substituted biphenyl-based HTMs T1N and T2N were observed to have better thermal properties than the commercial HTM NPB, with decomposition temperatures above 500 degrees C, and a 10 degrees C higher T(g). In EL devices with ITO/2-TNATA-(60 nm)/HTM(15 nm)/Alq3(70 nm)/LiF(1 nm)/Al structures, the disubstituted biphenyl-based HTMs with an asymmetric molecular structure D1N and D2N were found to have inferior luminescence efficiencies when compared to NPB, which has a symmetric molecular structure. However, M1N, which is substituted with a further two methoxy groups, was found to exhibit excellent luminance and power efficiencies, 4.88 cd/A and 1.36 Im/W respectively at 100 mA/cm2, which are higher by about 147% and 127% respectively than those of NPB (3.30 cd/A and 1.07 Im/W at 100 mA/cm2), due to better charge balance.
pp.762-763 silica subsffates. 3. Results and Discussion Annealing technique is important to modiff or improve material properties and an inevitable process for device fabrications. To detect the change of localized states in FIfO, we have performed CL as a function of annealing temperature from 300"C to 800'C. CL spectra of an as-deposited sample and of samples with Tu = 400"C, 600"C, and 800"C are plotted in Fig. 1. CL spectra changed&astically depending on T.. This shows that the localized states in FlfOrfilms sensitively changes with Tu, because the luminescence spectra are generally sensitive to localized states in the gap. This is the first observation indicating a change of the localized states in high-k materials with annealing. Since the leakage cunent also depen& on the annealing temperature, it is likely that a change of leakage current is caused mainly by a change of localized states distribution. As seen in Fig. 1, CL spectra have two peaks at 4.3 eY (290 nm) and 3.4 eV (370 nm). The peak intensities af,e plotted as a function of T. in Fig. 2. The 4.3 eV peak monotonously increases with annealing temperatures, while the 3.4 eV peak has a maximum intensity around 400 "C. Excited electrons and holes recombine through radiative and non-radiative processes as schematically shown in Fig. 3. Radiative processes are generally dre to band edge recombination, band tail recombination, or recombination through defects. On the other han4 there are non-radiative recombination processes through defect states.
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