Enhancement of photoresponse by enlarging the effective interface between conducting polymer and titanium oxide in photovoltaic device

The morphology of titanium oxide films, prepared via two different methods, oxidation following the evaporation of titanium and spin-coating a suspension of TiO2 nanoparticles, was investigated by scanning electron micrograph (SEM) and X-ray diffraction (XRD). SEM images indicated that the surface of the TiO2 film is rough and the pore size is large, compared with those of the TiO2 film, which results from the connected network of the TiO2 film. Pore filling is likely to be easier in the TiO2 film than in the TiO2 film due to its larger pore sizes. Poly(3-hexylthiophene) (PAT6) chains can be interrupted by the TiO network structure, as evidenced in UV-Vis spectrum. XRD revealed better crystallinity in the TiO2 film than in the TiO2 film. The investigation of the photoluminescence (PL) spectra revealed that PL of PAT6 is quenched when it was filled into the network pores. We prepared the photovoltaic devices using PAT6 as both sensitizer and hole conductor and titanium oxide and PV films as the electron conductor, to reveal the effect of the morphology of the titanium oxide films on the photovoltaic performance. An improvement of conversion efficiency by over twofold in the TiO2 cells compared with that of the TiO, cells was observed. These phenomena suggest that the photovoltaic performances of PAT-TiO2 (or TiOx)/PV cell were dependent on the interfacial morphology between both PAT6 and TiOx and PAT6 and PV.