Influence Of The Carrier Transport Layer On The Performance Of Organic Light-emitting Diodes

The carrier mobility of organic semiconductors is much lower than that of the inorganic semiconductors, which greatly restricts the development of organic semiconductor devices. Due to its prospect applications in the field of information display and solid-state lighting, the organic light-emitting diode (OLED) becomes a hot reaserch and product topics among all organic semiconductor devices. For OLEDs, the improvement of the carrier mobility in the devices can promote the balance of the carriers and results in a higher efficiency. Meanwhile, the carrier balance has a positive impact on the stability of the devices. Therefore, how to improve the carrier mobility is an interest sentific topic and also has a great application value. In this thesis, the role and effect of the carrier transport layers in OLED are studied, such as the effect of p-type doping on the electroluminescent performance, and the matching of carrier transport layers to the novel luminescent materials.Firstly, PCBM ([6,6]-Phenyl C61butyric acid methyl ester), a kind of C6o derivatives, is doped into the commonly used hole transport layer (HTL) PVK. The realized p-type doping enhances the hole mobility of PVK:PCBM HTL. The effects of this doping on the performance of various structural OLEDs are investigated. In addition, thermal annealing under the glass transition temperature of this HTL is found to play an important role to improve the device performance.Secondly, another C6o derivative ICBA is used to dope into PVK. The effects of this doping on the performance of various structural OLEDs with PVK:ICB A HTL are investigated.Then, the effect of ICBA and PCBM doping is compared. PCBM and ICBA are used respectively as weak electron acceptors in PVK. Their electron-trapping character can improve the hole transport in prepared devices. It relates to the LUMO of the doping. The LUMO of PCBM is lower than that of ICBA, and consequently the driving force for charge transfer of PVK:PCBM is higher than that of PVK:ICBA. As a result, the effect of PCBM doping is better than that of ICBA doping.Finally, the electroluminescent performances of two novel luminescent materials are inverstigated by designing different device structures. A good device structure can help the novel luminescent material to make full use of its advantages and realize a good device performance, which involves the improving the quality of thin films, reducing the quenching, suppressing the exciplexes, matching the energy levels and enhancing the transporting characteristics. In this study, good electroluminescent performances of two novel luminescent materials are obtained by matching carrier transport layers in devices to the novel luminescent materials. A red electroluminescence of Eu3+is obtained in the device containing a novel rare earth complex Eu(TTA)(2NH2-Phen)3. The thin film quality is improved and its electroluminescence quenching is reduced by using proper functional layers. In addition, the carrier balance in prepared deives is promoted. In the electroluminescen spectra of the bilayer device containing a novel blue-light emitting material TPhNI, except for the blue emission, a new peak around605nm is observed. This new peak is attributed to the exciplex between TPhNI and HTL. In order to obtain pure blue emission, various methods are adopted to suppress the exciplexes. The mechanisms of the electroluminescence of these new materials are discussed.