Effects of ZnO buffer layer and depth profiling analysis of bulk heterojunction organic solar cells

P.S. Mbule, T.-H. Kim, B.-S. Kim, H.C. Swart, O.M. Ntwaeaborwa
University of the Free State, ZA

Keywords: photovoltaic, P3HT:PCBM, ZnO, nanoparticles


Bulk heterojunction organic solar cells (BHJs) with ZnO nanoparticles buffer layer between the active layer and the aluminum (Al) top electrode were fabricated. The BHJs comprised of successive layers of poly(3,4ethylenedioxythiophene):poly(styrenesulfonate) (PEDOT:PSS), a blend of poly(3-hexylthiophene) (P3HT) and [6,6]-phenyl butyric acid methyl ester (PCBM) (active layer) and ZnO nanoparticles, spin-coated on a glass substrate precoated with indium tin oxide (ITO) . The devices were then annealed at 155 oC before (pre-annealing, device A) and after (post-annealing, device B) the deposition of the Al electrode. Device B showed improved photovoltaic properties compared to device A. This is attributed to improved charge carrier transport across the interface of the photoactive layer and the Al electrode. Depth profile analysis was carried out using time-of-flight secondary ion mass spectrometry (TOF-SIMS). The signals arising from 27Al, 16O, 12C, 32S, 64Zn, 28Si, 120Sn and 115In made it possible to identify the ITO, PEDOT:PSS, P3HT:PCBM, ZnO and Al cathode layers, respectively.