Organic thin-film transistors (TFTs) using the pentacene as an active electronic material have shown the mobility of 0.8 cm2Vs and the grains larger than 1 micrometers . Deep level transient spectroscopy (DLTS) measurements have been carried out on metal/insulator/organic-semiconductor (MIS) structure devices that have a depletion region at the insulator/organic-semiconductor interface. The very long capacitance transients were measured by the trapping of electronic charge carriers distributed in energy. Based on the DLTS characteristics, the energy levels of hole and electron traps in the obtained pentacene films were approximately Ev+0.24eV, Ev+0.31eV, and Ec- 0.69eV.
Multicolored electroluminescent (EL) devices has been realized utilizing poly((1-dodecyloxy-4-methyl-1,3- phenylene)(2,5"-terthienylene)) (mPTTh) as an emitting layer and tris(8-hydroxyquinoline) aluminum (Alq3) as an electron transport layer. A single layer EL device of mPTTh polymer emits orange-colored light. EL intensity increase as the thickness of Alq3 layer increases up to 30 nm, but the emission color becomes diversified when the Alq3 layer thickness is greater than 30 nm since the relative peak intensity of green EL from Alq3 layer grows. EL color is changed form orange to greenish orange depending on the thickness of Alq3 layer. EL efficiency of the double layer device was greatly enhanced by 3000 times in compared to that of single layer device. Alq3 layer in device acts as a hole blocking electron transporting layer and an emitting layer as a function of the thickness of Alq3 layer.
We report the polymer light emitting device with high quantum efficiency of electroluminescence made with the polymer blend. The quantum efficiency increases with the composition ratio of one component polymer up to about 500 times of the quantum efficiency of the other polymer.
We observe a new electroluminescent (EL) peak from a two-layer polymer device, which does not appear in EL spectra of each layer. The polymers of both layers are poly(p- phenylenevinylene) derivative with monoalkoxy substituents, poly(2-methoxy-1,4-phenylene- vinylene, abbreviated as PMPV), but dialyzed for different periods respectively. A new peak is located at 590 nm and has comparable intensity. The origin of this peak is discussed. Absorption and photoluminescence spectra are also measured and device properties show typical diode characteristics.
Surface potential technique was applied to determine the orientational order of NLO chromophores in poled polymers. The technique is sensitive enough to detect the electro-optic coefficient of the order of 10-3 pm/v and it is simple because it does not use any optics. It is purely electrical in contrast with other techniques. Relaxation behavior of poled DR1(1wt%)/PMMA was investigated using the surface potential technique. When the surface of the poled polymer was free from a metal electrode, the surface potentials decay monotonically with time. However, the surface potential measured on a metal electrode which was used as an electrode for poling showed an abnormal decay behavior. It was explained by the charge trap centers at the metal-polymer interface.
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