Two modes of Fourier-Transform Photocurrent Spectroscopy (FTPS) are presented for a fast and sensitive determination of photocurrent spectra of organic and dye sensitized solar cells. Furthermore, FTPS allows to spectrally resolve sub-bandgap absorption phenomena in P3HT, in organic P3HT:PCBM bulk heterojunctions and in hybrid P3HT/TiO2 solar cells. The sub-bandgap absorption in the P3HT:PCBM blend is dominated by a band due to the formation of a ground-state charge-transfer complex between the polymer and PCBM. In P3HT/TiO2 junctions such a charge-transfer complex band is not observed. Long-lived light induced sub-bandgap states appear in pure P3HT and in P3HT/TiO2 junctions after irradiation with E > 1.9 eV (c) 2007 Elsevier B.V. All rights reserved.