Impedance spectroscopy on organic bulk-heterojunction solar cells

We measured the electrical impedance spectra of organic bulk‐heterojunction solar cells based on an absorber blend of poly(3‐hexylthiophene) and [6,6]‐phenyl C61‐butyric acid methyl ester. Comparing the spectra of the non‐treated device and after two consecutive treatments with applied forward bias voltage at 110 °C, we observed a region in the semiconductor with a low conductivity, which was expanding after the treatments. We concluded that this region is a depletion region at the aluminium contact. This was confirmed by the bias dependence of the impedance spectra. (© 2005 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)