| Organic electroluminescent device, also known as organic light emitting diode, is a kind of solid state light emitting device by carrier injection which could directly converse electrical energy into luminous energy. Due to its low driving voltage and energy consumption, high brightness, flexibility in the choice of materials and easy realization of full color display, OLED shows its unique charm both in the display and illumination field. It still remains a large room for improvement such as light efficiency, service life, cost in mass production before OLEDs replace traditional technology in some application field.Organic light emitting diodes has a similar radiation theory of inorganic light emitting diodes. By a DC bias, electrons and holes will be respectively injected into the organic layer from the cathode and anode. Appropriate multilayer structures typically enhance the performance of the devices by lowering the barrier for hole injection from the anode and by enabling control over the electrons and holes recombination region, e.g., moving it from the organic/cathode interface, where the defect density is high, into the bulk. In the combination region, the electrons and holes combine and release energy to excite organic fluorescence molecular. Therefore, reducing the energy barrier between electrode and organic layer, improving and balancing the carriers’injection, enhancing the carriers’combination is an effective and feasible way to improve device performance.In consideration of the fact that there is an energy barrier between the work function of the widely used OLED anode materials--indium tin oxide (ITO) transparent conductive film and highest occupied molecular orbital of adjacent hole transport layer (HTL), leading to the difficulty in a further reduction in the driving voltage and increase of the anodic hole injection, we launched this work by ITO surface treatment or anode interface modification. We aimed to change the ITO surface morphology and oxygen content, improve the work function of the surface, thereby to reduce the gap between the HTL and anode to improve the hole transport. Literature research in this field shows that some reported treatment methods including chemical treatment, plasma treatment, and etc. work in the improvement of surface work function. But at the same time, we also discovered that these traditional treatment methods on the ITO surface have some shortages:oxygen content is enhanced limitedly and sometimes other contaminates may be introduced. Besides, the treatment effect has been proved to quickly decay with a time-dependence curve. So we put forward a new treatment method by plasma immersion ion implantation (PⅢ).First we determined to use oxygen as the plasma source by literature research. In our first set of experiment, we study the impact of bias voltage on modification effect. Ten pieces of sample was connected to a pulsed bias from1kV to10kV, and the results showed that PⅢ processed samples have a higher surface oxygen content and lower carbon content. But it is not coordinated with the increase of pulse bias as expected. However, through the first and second group of samples, PⅢ treatment can be confirmed efficacious in improvement of O and reduction of C. The third and forth group of samples were treated in another PⅢ equipment which was self-developed based on a vacuum chamber. These two groups aims at the implantation time dependence of ITO surface treatment effect. So we set the implantation time from10min to60min for different samples. The XPS results revealed that O/(In+Sn) is increased with the implantation time. However, the oxygen content was improved little with the time, but it had a sharp change from a merely plasma treated sample to a PⅢ treated sample. It is interesting to note that the estimated change of work function fits the O content, instead of the ratio of O/(In+Sn). |
PDF Full Text Request