Preparation Of Organic Layers Using Langmuir-Blodgett Method For Organic Electroluminescent Devices

Organic electroluminescent device(OLED) has broad application in lighting and display fields because of its excellent characteristics such as lightness, surface-emitting, self-illumination, flexibility and high transparency. The organic layer of OLED device is made of organic chemical materials. The present techniques used to prepare organic layer include vacuum evaporation, spin coating and screen printing etc. The molecules in organic layer prepared by those techniques are random arranged. Because carrier transport of carriers in organic thin-film with molecules arranged random is comparatively low, the OLED photoluminescence efficiency will be affected negatively. With Langmuir-Blodgett(L-B) technology, amphipathic molecules with hydrophilic head and hydrophobic tail are dispersed on the water under some suitable conditions, and then uniform monomolecular film is formed after gradually compressing occupied area, and finally the ordered molecular arrangement film is obtained by transferring the monomolecules to substrate. L-B technology enhances OLED electro-optical conversion efficiency because of the ordered molecular arrangement and high transmission rate.L-B technology has been applied in chemical field to prepare catalyst and improve its efficiency as well as the field of biologic semi-permeable film. However, reports about L-B technology applied in the preparation of organic layer are few, not to mention that about the functional mechanism of L-B membrane in the organic layer.My essay focuses on the L-B film preparation principle and technology of PVK---the prevailing hole transporting material in OLED device. In order to affirm the effect on the optical and electrical property of the PVK molecule alignment, PVK organic film is prepared by using spin coating and LB technology and build the LB and spin coating models. Afterwards, the optical and electrical property prepared are tested and compared by these kinds of technologies. The main work in this paper are as follows:① The theoretical basis of preparing organic film is built by using L-B technology, including organic materials uniformity and stability in the phase surface after being dissolved in toluene solvent. Then, the hydrophilic mechanism of substrate and functional mechanism between film and substrate are analyzed. Finally, the effect of molecule alignment on carrier transmission is illustrated.②The influences of different hydrophilic techniques on ITO transmittance and sheet resistance in the process of preparing PVK film are researched on. The effects of dispersant proportion on PVK films resistivity and thickness are analyzed. Monolayer of PVK LB film and multilayer of PVK LB films are prepared using self-regulating LB apparatus. The film thickness, UV-VIS absorbance spectrum, fluorescence spectrum, and electrical resistivity were tested respectively.③The spin-coating model of PVK is built based on the spin-coating law and research data in the experiment by changing the concentration and speed, and preparing the organic films using spin-coating process which have the same thickness with the L-B technology. And then, the film thickness, absorbancy and fluorescence spectrum are tested.④The mechanism that ordered molecule alignment improves carrier transporting is analyzed by discussing the concerned results according to the comparison of these two kinds of films performance parameters.