Study On Organic Near-infrared Light-emitting Devices And Thin-film Field-effect Transistors Based On Phthalocyanines

The 21st century is the era of knowledge economy. As the rapid developments of information technology, especially photoelectronics and microelectronics, the way of humans'working and living has changed unceasingly. As the main carriers of information technology, field-effect transistors and display devices play significant roles. After several decades'development, inorganic electronics have meet problems which are difficult to be solved. Compared with the inorganic semiconductors, the organic semiconductors have many advantages. The photo-electronic devices with organic semiconductor acting as active layer have wide application foreground, and become one of the research hotspots.Phthalocyanine (Pc) is a prominent class of organic molecular materials with high chemical and thermal stability. In particular, phthalocyanines (Pcs) and their derivatives can be used as remarkably functional materials and are finding the applications in a wide range of high technical fields such as organic light-emitting devices, organic field effect transistors, nonlinear optics, photovoltaic cells, chemical sensors, laser recording materials and even biomedical applications. Organic light-emitting devices and organic field effect transistors are both the most widely used organic electronic devices. The bigπconjugated system of Pcs is very important for the applications of near-infrared light-emitting devices and organic field effect transistors, so these devices based on Pcs have attracted attention of more and more researchers.Since the initial discovery of OLEDs in 1987, extensive research has been carried out on them in view of both academic interests and technological applications for full-color flat-panel displays with high brightness and rapid response. Most of the research has been focused on devices that emit light in the wavelength range from the blue-violet to visible light. Recently, NIR OLEDs have received attention due to their potential applications in optical communication. Emission efficiency of NIR OLEDs was generally low because of near-field deactivation by the host associated with coupling of the optically excited state to the vibrations of the organic molecule or polymer. However, materials used in NIR OLEDs have been limited in number, most of them were organic complexes containing trivalent rare earth ions such as Er3+, Nd3+, Tm3+ and Yb 3+. Only few organic materials containing no rare earth ions showed EL characteristic in NIR region. To search organic infrared emissive materials containing no rare earth ions has become a new challenge. In this paper, we have fabricated NIR-OLEDs employing the chloroindium phthalocyanine (ClInPc) and zinc phthalocyanine (ZnPc) for the first time. Room-temperature electroluminescence (EL) was observed near 0.9μm. As polymer based OLEDs have been attracting much attention as a promising inexpensive technology for large-area and flexible devices because the light-emitting layer of OLEDs can be prepared by wet process, such as spin coating or ink-jet printing. A soluble chloroindium 1, 8 (11), 15 (18), 22 (25)-tetra-(p-tert-butylphenoxy) phthalocyanine ((3-tert)ClInPc) was synthesized and characterized by MS, 1H NMR, elemental analysis, UV-vis and PL. For the purpose of testing its EL properties, single-layer OLEDs with the structure of ITO/(3-tert)ClInPc/Al were prepared first, but these devices did not show any measurable EL. The EL properties of the new compound were also studied in ITO/PVK:(3-tert)ClInPc/BCP/Alq3/Al devices. Room-temperature EL was observed near 0.88μm that effectively covered the first optical communication window near 0.85μm. At last, OLEDs were fabricated employing this ClInPc doped into Alq3. Near 0.88μm NIR EL was also demonstrated from these ITO/NPB/Alq3 :(3-tert)ClInPc/Alq3/Al devices. A soluble zinc phthalocyanine ((4-tert)ZnPc) was also synthesized and characterized by MS, 1H NMR, elemental analysis, UV-vis and PL. The NIR EL properties of the new compound were studied in ITO/PVK:(4-tert)ZnPc/ BCP/Alq3/Al devices and single-layer OLEDs with the structure of ITO/PVK:Alq3:(4-tert)ZnPc/Al. The emission processes of these phthalocyanines in the doped devices are discussed. These devices can be prepared by spin coating to simplify the fabrication process and so lower the manufacturing costs, which provide an effective method for the production of future NIR-OLEDs.Organic thin-film transistors (OTFTs) have received considerable attention recently because of their potential applications in flat panel displays, logic circuits and chemical sensors. The main factors motivating investigations of OTFTs are their lower cost and simpler packaging, relative to conventional inorganic TFTs, and their compatibility with flexible substrates. During the past ten years, the performance of OTFTs has dramatically improved to the level of a-Si:H TFTs by employing high-mobility materials and proper device structures. We have fabricated CuPc TFTs with PMMA or P(MMA-co-GMA) gate insulator. These devices behaved fairly well and presented satisfactory p-type electrical characteristics. We investigated the structural and morphological properties of the CuPc thin films deposited on polymeric insulators such as PMMA or P(MMA-co-GMA) and the electrical characteristics of CuPc TFTs with PMMA or P(MMA-co-GMA) gate insulator. We found that the crystallinity and order were better for CuPc film deposited on P(MMA-co-GMA) compared with that deposited on PMMA. The CuPc TFTs with P(MMA-co-GMA) gate insulator showed higher field-effect mobility, larger on/off current ratio and lower threshold voltage compared with the CuPc TFTs with PMMA gate insulator. The result indicates that the device electrical characteristics are highly correlated with the structural and morphological properties of the CuPc films and the CuPc/Polymer interface. The better crystallinity of the CuPc films on P(MMA-co-GMA) and the better CuPc/P(MMA-co-GMA) interface will lead to improved device performance. The spin-coated PMMA or P(MMA-co-GMA) gate insulator also offers compatibility with organic semiconductors, flexibility and simple processing steps, which make them very attractive for the production of future flexible all organic TFTs and displays. These results indicate that both PMMA and P(MMA-co-GMA) are promising candidates for replacing inorganic gate insulators hardly compatible with flexible substrates in OTFTs.For modeling and design of optoelectronic devices, the optical functions of each layer should be known. First of all, the optical properties of approximately transparent P(MMA-co-GMA) thin film were studied by spectroscopic ellipsometry using a variable angle spectrometric ellipsometer (VASE). Emphasis is placed on the study of the optical properties of Pcs using VASE. As an example, the optical functions of oxotitanium phthalocyanine (TiOPc) thin film were studied by spectroscopic ellipsometry for the first time with four different methods. The absorption coefficient of TiOPc film could be obtained from extinction coefficient. The spectrum was explained with its energy levels structure. The optical band gap (Eg) was derived from the edge of the absorption. At last, we studied the optical properties of zinc phthalocyanine (ZnPc) and a series of soluble substituted ZnPc and investigated the effect of substitutes on the optical properties. It has been found that the substituted groups on the conjugated phthalocyanine macrocycles strongly influence resonance wavelength and abnormal dispersion of the thin films. The influence of the kind of peripheral groups on the resonance wavelength is very weak because two kinds of peripheral groups are very similar in this experiment. However, the influence of the substitute positions on the resonance wavelength is strong. In the visible region, the resonance wavelength and abnormal dispersion region of all the phenoxy substituted ZnPc films are red-shifted compared with those of ZnPc film. However, the resonance wavelength and abnormal dispersion region ofα-substituted ZnPc red-shift longer than those ofβ-substituted ZnPc. In the UV region, the resonance wavelength and abnormal dispersion region of the films are red-shifted forβ-phenoxy substituted ZnPc, but blue-shifted forα-phenoxy substituted ZnPc. These results may be caused by the different conjugated effect and induced effect produced by substitute groups in different position. The optical band gap of each material was also derived from the edge of the absorption.