Photovoltaic devices based on PPHT: ZnO and dye-sensitized PPHT: ZnO thin films

We have investigated the optical and photovoltaic properties of hybrid organic solar cells based on the blend of poly-3-phenylhydrazone thiophene (PPHT):ZnO and PPHT:dye:ZnO. In this architecture, ZnO and PPHT were the electron acceptor and donor, respectively, and dye was used both as acceptor as well as sensitizer to enhance the photon absorption in visible region. These results showed that on incorporation of dye in PPHT: ZnO composite the light absorption, exciton separation and photocurrent under white light dramatically enhanced. The dependence of photovoltaic parameters on the weight fraction of ZnO in PPHT: ZnO was also investigated. It is found that the device with 45% of ZnO in both composites exhibits the best photovoltaic performance. The thermal annealing of PPHT: ZnO-based device gives rise to a significant increase in power conversion efficiency as evident from the measurements of incident photon to charge carrier efficiency (IPCE) spectra and current-voltage characteristics under illumination. The absorption band of PPHT: ZnO blend becomes stronger and the absorption peak ascribed to PPHT is shifted towards the longer wavelength region (red shift) upon thermal annealing. The effect of solvent used for thin-film fabrication was also studied. It is also observed that the fluorescence (FL) quenching and solar cell efficiency were found to be strongly dependent on the solvent used for spin coating. (c) 2008 Elsevier B.V. All rights reserved.