Nanostructured Electrodes and Photoactive Layers for Efficient, Stable and Flexible Organic Photovoltaic Devices

Abstract

This work presents our latest results for conventional and inverted organic photovoltaic (OPV) devices based on polymers such as poly(3-hexylthiophene) (P3HT) and poly[N-9”-hepta-decanyl-2,7-carbazole-alt-5,5-(4’,7’-di-2-thienyl-2’,1’,3’-benzothiadiazole) (PCDTBT) blended with fullerene derivatives such as [6,6]-phenyl C61-butyric acid methyl ester (PC61BM) and PC71BM. It is observed that by controlling the morphology of acceptor and donor domains in the BHJ photoactive films higher power conversion efficiency (PCE) and performance for OPV devices can be achieved, with the best efficiencies demonstrated for the P3HT:PC61BM and PCDTBT:PC71BM devices exceeding 4% and 7%, respectively. Here, the interplay between fabrication processes and the performance of the devices is investigated to achieve optimum PCE, short-circuit current and open-circuit voltage for the OPV devices. In addition to contact and BHJ films, a flexible solar cell requires a flexible transparent conductor (TC). We report our results for conductive electrospun nanofiber based TCs as replacements for the brittle indium tin oxide (ITO) used for solar cells on glass substrates. These novel nanofiber TC web and their associated flexible substrates act as new platforms for fabrication of low cost, flexible solar cells. Performance of the TC is compared to other novel TCs in terms of transparency, sheet resistance and flexibility. The performance of the nanofiber TC webs is manifested in OPV devices that employ these TCs as the transparent electrode and demonstrate comparable performance to the devices using ITO electrodes. This work demonstrates the significance of novel materials and deposition technologies for enabling efficient and stable OPV devices for roll-to-roll manufacturing on flexible substrates.