Carrier mobility in organic semiconductors with an exponential density of states under the framework of admittance spectroscopy

The carrier transport in amorphous organic semiconductors with an exponential density of states is systematically studied under the framework of admittance spectroscopy. Due to the exponential distribution, the slope of the double logarithmic curve of current density versus voltage is expressed as b+2, where b relates to the width of the density of states. And the mobility is proportional to nb, where n is the density of carrier. In this case, the peak frequencies of the negative differential susceptance and imaginary part of impedance turn out to be functions of parameter b. Therefore, the relation between transit time and mobility will be a linear function of parameter b. Applying our model to interpret experimental data of both small molecular and polymeric materials are illustrated. The contributions of electric field and of carrier density to mobility are discussed.