Using admittance spectroscopy to quantify transport properties of P3HT thin films

The charge transport properties of organic electronic materials are of critical importance for the understanding of the operation of organic photonic devices.We show in this study that admittance spectroscopy (AS), which is a measure of the frequency dependent capacitances of organic electronic materials, can be used to determine charge carrier mobilities and transport parameters in organic photovoltaic materials. A plot of the negative differential susceptance versus frequency yields a maximum at a frequency. The position of the maximum is related to the average carrier transit time. Using AS, we study the hole transport properties of thin films of poly(3-hexylthiophene) (P3HT) based materials for organic photovoltaic applications, including pristine P3HT, and P3HT doped with [6,6]-phenyl-C61-butyric acid methyl ester (PCBM). We demonstrate that AS can be used to extract hole mobilities of P3HT and P3HT: PCBM with a thickness of ∼350 nm. For P3HT: PCBM, copper phthalocyanine is used as an electron trapping layer to reduce the effect of negative capacitance.