Time-Of-Flight Technique to Examine Carrier Blocking Nature in Organic Light Emitting Diode

Abstract

In organic light emitting diodes, carrier-blocking property at organic hetero interfaces is one of important factors to get better performance, but the factor have not been well investigated experimentally. In this study, we proposed a new usage of time-of-flight (TOF) technique to quantitatively examine the carrier behavior in operating device. The measurement was demonstrated for ITO| α-NPD(1100 nm) |Alq₃(60 nm)|Al(100 nm) device. TOF signal was successfully observed under the influence of actual current flow. For hole transport from ITO to Al electrode, delayed-transport and blocking nature at α-NPD/Alq₃ was clearly observed. In contrast, for electron transport in the same direction, no delayed transport was detected. This result was consistent with the possible energy barrier at the interface, indicating the feasibility of this technique to examine carrier blocking nature in electronic devices. The method to analyze the TOF in detail will be discussed. [DOI: 10.1380/ejssnt.2012.315]