Effect of UV-ozone treatment on ITO and post-annealing on the performance of organic solar cells

In this paper, the influence of the ultraviolet (UV)-ozone treatment of indium tin oxide (ITO) surface and the active layer post-annealing treatment on the performance of organic solar cells were investigated. Bulk heterojunction organic solar cells based on the blend of poly(3-hexylthiophene-2,5-diyl) (P3HT) and [6,6]-phenyl C-61 butyric acid methyl ester (PCBM) were fabricated. It is found that the devices with the UV-ozone treatment for 5 min on ITO substrates show the better performance, compared with the devices without this treatment. The results demonstrate that the short-circuit current density (J(sc)) and fill factor (FF) could be improved by the post-annealing treatment. The devices with both treatments together show the best performance, with the increase of J(sc) from 2.68 mA/cm(2) to 4.13 mA/cm(2) and the enhancement of FF from 32.2% to 38.8%. Therefore, the power conversion efficiency is improved from 0.62% to 1.08%. The morphology of the active layers with and without the post-annealing treatment was characterized by atomic force microscopy. (C) 2008 Elsevier B.V. All rights reserved.