Determination of Carrier Mobility for Thin-Film Organic and Hybrid Solar Cells through Transient Photoconductivity

Transient photoconductivity is widely used to study decay characteristics of organic solar cells. For thick devices (> 1μm), the Time of Flight (TOF) technique is one such transient technique that is used to extract carrier mobility. TOF determines the amount of time it takes for photon-generated charge carriers to travel from one electrode to another in order to calculate mobility. However, in thin film organic semiconductors, TOF has shown to be difficult to implement due RC time constant limitations and generation of charge throughout the device.

Recently, transient photoconductivity has been used to measure carrier mobilities in organic thin-film solar cells that reproduced numbers found in literature. To confirm the validity of transient photoconductivity as a means to find mobility, experiments were performed on poly (3-hexylthiophene) (P3HT) and [6,6]-phenyl C61-butyric acid methylester (PCBM) solar cells. The results were compared with Space Charge Limited Current mobility numbers for the same device. Transient photoconductivity was found to be a sound technique under certain conditions. The transient photoconductivity technique was further used to calculate carrier mobility for P3HT:Cadmium Selenide (CdSe) hybrid solar cells, with results agreeing with those found in literature.