Determination of carrier mobility in phenylamine by time-of-flight, dark-injection, and thin film transistor techniques

The hole transport property of a phenylamine-based compound, 4, 4′, 4″ -tris(n - (2-naphthyl)- n -phenyl-amino)-triphenylamine, was independently studied by time-of-flight (TOF), dark-injection space-charged-limited-current (DI-SCLC), and thin film transistor (TFT) techniques. With UV-ozone treated gold as the injecting anode, clear DI-SCLC transient peaks were observed over a wide range of electric fields. The hole mobilities evaluated by DI-SCLC experiment were in excellent agreement with the mobilities obtained from the TOF technique. The injection contact was demonstrated to be Ohmic by an independent current-voltage (J-V) experiment. However, with the same injecting electrode, the mobility deduced from the TFT method was found to be 9.8× 10-7 cm2 /V s, which was about one order of magnitude smaller than the TOF mobility (∼1.2:× 10-5 cm2 /V s). The origin of the discrepancy is discussed.