Interface Band Gap and Charge Trapping in Bulk Heterojunction Solar Cells

Bulk heterojunction devices were studied using Fourier Transform Photocurrent Spectroscopy and impedance spectroscopy. The photocurrent below the absorption edge reveals the charge transfer transition and we present experimental evidence confirming that it is due to the presence of the acceptor PCBM. The impedance spectra reveal additional polarization under illumination. We propose a model for photogenerated charges confined in isolated material regions which contribute to this additional polarization.