Charge-carrier mobility in an organic semiconductor thin film measured by photoinduced electroluminescence

With existing methods it is difficult to measure the mobility of semiconducting thin films that have submicron thickness and submicrosecond charge-carrier transit time. To simplify these measurements we demonstrate a technique that is a combination of the time-of-flight and transient electroluminescence methods. The technique is fundamentally optical in that it decouples the carrier transient signal from the device charging circuit and hence removes the RC time constant constraint that limits existing methods. The technique was applied to measure electron mobility in a tris(8-hydroxyquinoline) aluminum (AlQ3) thin film. Results agree well with mobility values obtained using other methods.