Charge transport properties of bulk-heterojunction organic solar cells investigated by displacement current measurement technique

We have investigated charge transport properties of bulk-heterojunction (BH) solar cells in which P3HT (Poly(3-hexylthiophene)) and PCBM ([6,6]-phenyl-C₆₁-butyric acid methyl ester) are used as the active layer, by using the displacement current measurement (DCM) method. In order to investigate the charge transport properties of the BH solar cells, we fabricated a dedicated device that consists of P3HT and PCBM, and used the DCM method to measure the charge distribution of the devices with different composition ratios of P3HT and PCBM. DCM data suggested that a BH film with 50 wt% of PCBM exhibits a preferable charge transport property suited for BH solar cells. We confirmed that the DCM results are consistent with the measured performance of the BH solar cells, indicating that the DCM method is a simple and effective method for optimizing the structure of BH solar cells as well as other electronic devices composed of binary materials.