Injection-charge extraction by linearly increasing voltage in metal-insulatorsemiconductor structures (MIS-CELIV) is applied for the hole mobility measurement of N,N'-Bis(naphthalen-1-yl)-N,N'-bis(phenyl)-benzidine (NPB), which is a standard hole-transporting material for organic light-emitting diodes. Ideal transient currents in agreement with the theory are observed in the NPB film due to its amorphous and homogenous structure, which is regarded as a continuous dielectric. This ideal response

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... enables us to discuss the validity of the MIS-CELIV mobility by comparing its absolute value with that of the conventional space-charge-limited current method. In addition, to establish an experimental guideline for precise measurements, the effect of the voltage drop on the insulator is investigated.