We report on inverted solar cells using amine-containing polymer (polyethylenimine ethoxylated, PEIE) modified fluorine-doped tin oxide (FTO) as the electron-collecting electrode. PEIE lowers the work function of FTO from 4.6 eV to 3.8 eV, measured by Kelvin probe, sufficiently low for collecting electrons in solar cells. With the FTO/PEIE electrode, inverted solar cells based on poly[(4,8-bis-(2-ethylhexyloxy)-benzo[1,2-b:4,5-b'] dithiophene)-2,6-diyl-alt-(4-(2-ethylhexanoyl)-thieno[3,4-b]thiophene)-2,6-diyl]:phenyl-C-61-butyric acid methyl ester exhibited an open-circuit voltage of 0.70 +/- 0.01 V, a short-circuit current density of 15.2 +/- 0.2 mA/cm(2), a fill factor of 0.60 +/- 0.01 and a power conversion efficiency of 6.3 +/- 0.2% averaged over 9 devices under 100 mW/cm(2) AM1.5 illumination, which is comparable to the solar cells fabricated on indium-tin oxide glass substrates. In addition, we found that ultraviolet light-containing illumination can reduce the work function of bare FTO from 4.66 eV to 4.34 eV presumably because of the desorption of oxygen trapped in FTO. (C) 2013 Elsevier B.V. All rights reserved.