Capacitance methodology for investigating defect states in energy gap of organic semiconductor

Organic semiconductor materials have been applied diffusely in photoelectronic devices, such as solar cells, light emitting diodes, etc. Defect states in energy gap are one of most significant physical parameters affecting the charge transport in organic devices. Hence, investigating defect states plays a vital role for improving device performance. As one of the most widely applied method of investigating defect states in organic materials, capacitance measurements mainly include capacitance-voltage, capacitance-frequency, forward bias capacitance-voltage and so on, however these measurements have not been comprehensively interpreted and even have not been used properly in detection range. Therefore, in this review, the theory of each capacitance measurement and its application in organic semiconductor are compiled. The comparison of advantages and disadvantages among these different capacitance measurements and detailed description of their detecting range have been carried out. And a following outlook comprising the future developments of capacitance measurement is given. In the end, a table including characteristics for each capacitance measurement is created so as to be understood and used by researchers.