电容耦合氧等离子体处理ITO基片对OLED的影响

在不同条件下采用电容耦合氧等离子体处理用于有机电致发光（OLED）的ITO基片，使用接触电势法测量了基片表面功函数的改变。研究发现，氧等离子体处理可以有效地提高ITO表面的功函数。X射线光电子能谱的测量揭示了其本质：氧等离子体处理可以提高表面氧原子的含量，同时降低ITO表面锡／铟原子的比例，由此导致了ITO表面功函数的提高。高功函数的ITO可降低空穴由ITO向OLED空穴传输层中注入空穴的势垒，从而提高OLED器件的性能。进一步的基于联苯二胺衍生物NPB／8-羟基喹啉铝（Alq3）的标准器件的研究证明了这一点。研究同时发现，在相同的真空和氧压条件下，保持处理时间不变，随着射频激发功率的升高，ITO表面功函数会逐渐降低。这个功函数的降低，使得OLED器件的驱动电压升高且电流效率减小。因此使用电容耦合氧等离子体处理的ITO来制备OLED器件，需要在优化的条件下进行，以达最佳效果。在本实验系统下处理条件为射频功率100W、时间25s。

Influence of the Capacitive-coupling Oxygen Plasma Treatment on the ITO Substrate for OLED

Indium tin oxide （ITO） substrates were treated by capacitive-coupling oxygen plasma under different conditions. The work functions of ITO substrates were measured via contact potential method. It was found that the ITO work function could be significantly increased by oxygen plasma treatment. The analysis of X-ray photoelectron spectroscopy （XPS） showed that the oxygen content in the surface of ITO increased and the ratio of Sn/In reduced when the ITO surface was treated by oxygen plasma, resulting in the increment of ITO work function. The standard organic light-emitting devices （OLEDs） were fabricated on the treated ITO substrates and the device performances were studied. Due to the reduction hole injection barrier from ITO to organic layer,the device performance based on plasmatreated ITO substrate showed a significant improvement. Meanwhile, experiments also revealed that the ITO work function decreased slightly with increasing plasma power. This reduction of work function will decrease the device efficiency and increase the driving voltage. Thus,when processing plasma treatment to ITO surface, there is an optimized condition for obtaining the best OLEDs performance,which is 25 s under plasma power of 100 W in our experimental system.