An Analytical Model to Justify the Frequency Dependence of the Photocapacitance Effect in Organic Heterojunction Devices

The photocapacitance effect in organic heterojunction devices was investigated, revealing that it depends on the measuring frequency. The frequency dispersion was measured for the structure of ITO/CuPc/PTCBI/Al and in order to justify the origin of the frequency dependence, an analytical model was introduced based on the emission and capture rates of traps. On the basis of the model, traps lifetime could be decreased by exposure to light so that the junction capacitance increases at low frequencies. Furthermore, the degree of density of traps being dominant in either n-type or p-type regions mostly controls the behavior of the dispersion curve.