Charge-retraction time-of-flight measurement for organic charge transport materials

This letter describes an all-electrical technique, charge-retraction time-of-flight (CR-TOF), to measure charge carrier mobility through an organic layer. Carriers are injected and accumulated at a blocking interface, then retracted. The retraction current transient is nearly indistinguishable from a traditional time-of-flight photocurrent. The CR-TOF technique is validated by measurement of the hole mobility of two well-known compounds, $4,4′,4″$-tris[$N$-(3-methylphenyl)-$N$-phenylamino]triphenylamine and $4,4′$-bis[$N$-(1-naphthyl)-$N$-phenylamino]biphenyl, utilizing 1,3,5-tris(⁠$N$-phenylbenzimidazol-2-yl)-benzene as a hole-blocking layer. A sample layer thickness of less than $300nm$ can be used for the measurement.