Study On Organic Light-emitting Devices With An Emitting-layer Based On Starburst Molecules

Organic light-emitting diode(OLED) is considered to be the most promising next-generation technology of display and lighting. OLEDs based on polymer, which can be fabricated by solution process, such as spiral belt, inkjet printing, screen printing and other low cost technology implementation, has the natural advantage and received wide attention. However, the white OLEDs still has a long way to go before being applied in commercial production, and some difficulties still exist in film-forming method by solution processing, such as film can be destroyed by the solution of upper film in OLEDs of multilayer structure and charge injection faces high level barriers in the interface between electrode and emitting layer. Star-burst molecules have the advantages such as good film-forming property, three-dimensional, monodispersity and so on and potential value in the field of organic optoelectronic materials. This paper mainly study the two aspects of the experiment based on the advantage of well film-forming of star-burst molecule materials. And the main results were as follows:1. Due to the defect that the exciton in star-burst molecules can quench because of aggregation in the OLEDs, we fabricate OLEDs by means of doping with small molecule material as emitting layer and optimize the luminescence performance of devices. Finally, the high-performance green OLEDs has a largest brightness of 19900 cd/m2, current efficiency of 10.1 cd/A, the turn-on voltage of 3.5 V. At the same time, we fabricated and optimized some red OLEDs with red emitting materials by the same mean. On low doping concentration, the host material can emit blue light because of energy transmission incompletely and white OLEDs have been fabricated. On the basis of preparation, we doped red material with blue-emissive material to fabricate white OLEDs devices. We constantly adjust the doping ratio of red and blue light material to make sure that the white OLEDs are according with white OLEDs color coordinates(0.33, 0.33). Finally we got the white OLEDs whose spectrum is pure, luminous performance is superior.2. Contrast with doping white OLEDs, single molecule OLEDs have the advantages of simple structure and stable spectrum. On the basis of a series of single molecule white emitting materials designed and synthesized by our team independently, we fabricate and optimize white OLEDs in the method of film-forming by solution spinning paint. After testing the spectrum and light-emitting performance of finished white OLEDs, we compare the peak strength of three colors: red, green and blue. We also contrast the device CIE coordinates with CIE coordinates(0.33, 0.33) of pure white light. So, we constantly design and optimize quality proportion of red, green and blue on the molecular structure of single molecule white materials and in the end we synthesized single molecule white light material. The finished OLED with single molecule white material shows the CIE coordinates of(0.326, 0.326) with the voltage of 10 V and it belongs to the pure white OLED. It has a turn-on voltage of 6 V, the maximum brightness of 3300 cd/m2, current efficiency of 1.3 cd/A.3. Due to the high energy level barrier in the face between the active layer and electrode, OLEDs still has a long way to go before being applied in commercial production. P-type dopant and n-type dopant are used as HTL and ETL of OLEDs respectively. As the concentrations of p-type doping increases to 5%, the performance of the device achieve the best condition, and the maximum brightness is as high as 12257 cd/m2, current efficiency is as high as 3.04 cd/A. Compared with reference device and we can found that p-type doped as hole transport layer in OLEDs enhance hole injection obviously and greatly improve the luminous performance. When n-type doping concentration was 10%, the turn-on voltage of the device is less than 4 V and 1.5 V less than OLEDs in conventional structure. The OLED has a largest brightness of about 7087 cd/m2. N-type doping as electron transport layer can greatly alleviate the barrier level and forcefully enhance the electronic injection of the interface between cathode material and emitting layer.