P3HT:PCBM based solar cells: a short review focusing on ZnO nanoparticles buffer layer, post-fabrication annealing and an inverted geometry

Paper presented to the 3rd Southern African Solar Energy Conference, South Africa, 11-13 May, 2015.Today, bulk heterojunction (BHJ) organic solar cells (OSCs) dominate modern age research in renewable solar energy. In recent developments, the ultimate goal is to improve the general performance of the BHJ-OSCs to enable them to compete on an equal footing basis with conventional silicon photovoltaic cells. In this presentation, we review the fundamental parameters that have been reported to improve the general performance of the BHJ-OSC devices. These parameters include, among other things, the use ZnO nanoparticles electron transport layer (ETL) inserted between the top electrode and the photoactive layer, annealing procedure and device geometry. The BHJ-OSC devices constructed in this study comprised of successive (bottom up) layers of (3,4ethylenedioxythiophene):poly(styrenesulfonate) (PEDOT:PSS), a blend of poly(3-hexylthiophene) (P3HT) and [6,6]-phenyl butyric acid methyl ester (PCBM) layer, zinc oxide (ZnO) nanoparticles and aluminum (Al) metal top electrode. These layers were deposited on indium tin oxide (ITO) coated glass substrates. The device construction was also inverted (top down) in order to evaluate the effect of inversion on the power conversion efficiency and the general performance of the devices. The devices were annealed at 155 oC either before (pre-annealed) or after (post-annealed) the deposition of the Al top electrode. Post-annealed devices showed improved photovoltaic (PV) characteristics when compared to pre-annealed devices. Furthermore, we discuss the performance of inverted geometry in comparison to ZnO nanoparticles and nanoflakes as buffer layers.cf201