Characterization of large area flexible plastic solar cells based on conjugated polymer/fullerene composites

Abstract

The development of solar cells based on composites of organic conjugated semi-conducting polymers with fullerene derivatives can provide a new method in the exploitation of solar energy. Organic solar cells must fulfill the criteria of stability, efficiency and reduction of production costs to find new applications. Specially, the bulk donor-acceptor heterojunctions between conjugated polymers and fullerenes have been successfully utilized for photovoltaic devices with high carrier collection efficiency compared to the devices made from single components. In this work we present measurements of the photovoltaic response of bulk donor-acceptor heterojunction between the conjugated polymer (as a donor, D) poly(3-octylthiophene), P3OT and fullerenes, (as acceptor, A), deposited between indium tin oxide and aluminum electrodes. These devices are based on ultrafast, reversible, metastable photoinduced electron transfer and charge separation. The quality and homogeneity of composite films as well as the choice of the substrates strongly influence the efficiency of the solar cells. One of the most important limiting factors in the performance of this present types of molecular solar cells based on interpenetrating networks of conjugated polymers and fullerene derivatives is the charge carrier transport in the active layer. This transport is driven by the electrical field provided externally by the top and bottom electrodes with different work functions. We present here efficiency and stability studies on large area (6 cm x 6 cm) flexible plastic solar cells with monochromatic energy conversion efficiency ηe about 1.4% and carrier collection efficiency nearly 20%.