Impedanc analysis of the organic light emitting displays containing carbon nanotubes

Carbon nanotubes (CNTs) have been widely utilized in the organic light emitting displays (OLEDs). Polymer-based OLEDs with CNT inclusion with the emitting layer, especially for alternating current (AC) driving onews, exhibited higher luminance than OLEDs without CNTs. But the current level of AC OLEDs with CNTs was not clearly reported in other publications suggesting poor current characteristics. This might be caused by the unwanted bypass current paths through CNT networking within the devices. Thus, controlling the properties of CNTs mechanically or chemically is required for high efficiency devices. Here, CNTs were mixed with an emitting layer to be a CNT-polymer composite by varying the concentration of the CNTs. The luminance of the CNT-OLEDs was higher than the reference OLEDs without CNTs. The current could be roughly 30-40% reduced. One of the primary reasons for this high efficiency is considered to be the micro-capacitor effect caused by CNT networking. This CNT effect was examined by the impedance analysis, which could also explain low current mechanisms. Due to AC driving, the capacitive reactance could contribute to the device. Consequently, The CNTs incorporation within OLEDs would improve the efficiency of OLED.