Impedance spectroscopy characterization of inverted type organic solar cells based on poly(3-hexylthiophene-2,5-diyl)

Abstract

Poly(3-hexylthiophene-2,5-diyl) (P3HT)-based inverted type organic solar cells with different configurations have been extensively studied by impedance spectroscopy under different applied bias voltage in dark. Using an equivalent circuit model, separate regions of frequency-dependent impedance spectra could determine bulk and interface properties of P3HT-only and ZnO/P3HT devices. Two semicircles in the high and low frequency regions were observed in the impedance spectra of all the devices. The semicircle in high frequency region could be attributed to geometrical contribution of P3HT bulk layer. In the case of P3HT-only devices, the low frequency semicircle could be related to the interface between the bottom electrode (ITO or FTO) and P3HT. Meanwhile, for ZnO/P3HT devices, the low frequency semicircle corresponded to the interfacial process between the ZnO and P3HT. The ZnO nanorod arrays device exhibited larger interfacial area for exciton dissociation than the ZnO film device, hence resulting in improved power conversion efficiency. © 2014 AIP Publishing LLC.