Electrode Modification In OLEDs

Organic electroluminescence (OEL) phenomenon was found out first time in Nineteen thirties, but luminescent efficiency and lightness were not noticeable, so as to the OEL phenomenon.Untill1987, when Dr.Tang and Vanslyke firstly used organic semiconductor material Alq3as organic luminescent material, they got great promoted luminescent characteristics of OLED,then OEL obtained more attention.The huge investment in research and development had been carried out by research staffs and lots of companies for a long time.Since then, OLED has became the prospective display and lighting technology after liquid crystal display technology. However, there are many difficulties have not been solved yet when OLED is commercial applied.Such as luminescence merchanism is not perfect, the same to the lifetime and stability of devices. It is hard efforts made by research staffs, around above problems, that became the main research fields.In these fields, electrode modification is one crucial task, and we carried out several research works as follows:(1) About anode modification, we made use of P type semiconductor material CuI to modify ITO anode and manufactured devices with the structure of ITO/CuI/NPB/Alq3/Al. I-V and lightness test indicated that luminescent efficiency and luminance were promoted when the devices’ITO anode was modified. Ultraviolet photoelectron spectroscopy (UPS) test found out that the work function of ITO was enhanced about0.7eV.In addition, we also used MoO3and PbI2etc semiconductor materials trying to modify ITO anode, at the same time we prepared correspongding devices to research, but the two kinds of materials gained different effect in anode modification.(2) Enlightened by ITO surface dispose technology, we probed into several plasma treatments. Firstly, we researched impact of Ammonia plasma treatment on ITO anode modification, and experiments results indicated that the work function of ITO was increased, and based on this anode the devices’luminescent characteristcs were promoted greatly. Secondly, we had checked out the conclution that Oxygen plasma treatment can enhanced ITO’s work function, also we analysed the cause in essence.(3) About cathode modification, we made our effords based on different structures of devices about cathode modification, the effords were reflected in the fourth chapter of this thesis.We firstly made elementary research in the symmetrical structure devices surrounding alternating current electric field.Then we researched the inverted structure of devices,and testing the cathode modification effect, also we pointed out electron transport material Alq3and A1Oxide film deposition can modify ITO cathode effectively,and analysed the cathode modification mechanism.At the end, we analysed LiF’s modify effect in positive structure devices toward Al cathode,and we also provided the modification mechanism.