Research On Improving The Performance Of The Bulk Heterojunction Organic Solar Cells

Due to their potential of low-cost, light-weight, flexibility and reel-to-reel coating applied in large area, Organic Solar Cells (OSCs) have attracted substantial interests and investigation. However, the photoelectric conversion efficiency (PCE) is still low compared with silicon-based solar cells. Now, most researches concentrate on their attention to the treatment of devices and to develop new kind organic materials. So, in this thesis, we investigate to improve the performance of OSCs by treating ITO, inserting Pentacene and using a new kind of materials. Considering of the progress of current research and laboratory conditions, the bulk hetrerojunction OSCs are fabricated.First, 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 the OSCs are investigated. 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) can 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/cm² to 4.13 mA/cm².Second, the Pentacene layer is inserted in the OSCs to improve the sunlight absorption of the devices. When the thickness of Pentacene is 8 nm, the devices have best performance. The morphology of the Pentacene with different thickness is characterized by atomic force microscopy (AFM). We find that the surface morphology and film forming properties of the Pentacene have great impact on the devices. When the thickness of Pentacene layer continued to increase, the characteristic parameters of the devices would reduce, because the contacts between the organic layer and the PEDOT: PSS decreased.At the end, a new kind of polymer PDDTV which has a low energy gap is investigated. PDDTV showed a broad and strong absorption in the visible region. We fabricate OSCs by using this polymer as a donor to study its photovoltaic properties. But the performance of the devices is bad, due to the poor solubility of the material.