Photovoltaic devices with an active layer from a stamping transfer technique: single layer versus double layer.

In this study, organic photovoltaic devices with single or double-layered active film were prepared from a stamping transfer technique. A P3HT/PCBM single-layered active layer and a ratio-controlled P3HT/PCBM double-layered active can be successfully fabricated with the help of ultraviolet curable polycarbonate films via a stamping transfer technique. The maximum conversion efficiency values 2.85 for a single active layer transferred device and 3.24% for an optimized double active layer transferred device. Even though transferred double layers should have a sharp interface boundary, an intermixed zone with a concentration gradient was generated by the interpenetration of a donor-rich layer and an acceptor-rich layer in a thermal annealing process. The generation of the intermixed zone is confirmed by Auger electron spectroscopy. The enhanced conversion efficiency levels are attributed to the increased efficiency of the carrier transporting process, which is due to the fact that the concentration gradient is combined with the efficient charge generation from the bulk heterojunction layers.