Observation of Carrier Behavior in Organic Photoconductor by Transient Space-Charge Measurement

Space-charge measurement by an acoustic technique such as the pulsed electroacoustic method has often been applied to insulating materials with low carrier mobility. However, some functional materials have high carrier mobility so that the evolution of space charge is difficult to observe. In this study, a new measurement method which can measure the rapid transient of space charge was proposed and applied to a photoconductive material. The space charge after the illumination by a light pulse was traced with an interval of several hundred microseconds. It was observed that a charge packet traveled through the material after being generated at the illuminated side. The behavior was interpreted into the average carrier mobility. The mobility was in good agreement with that obtained by the conventional time-of-flight method using a transient current.