(579g) In-Situ Polymerization of 3-Hexylthiophene Within Mesoporous Titania Films

The present study focusses on the in-situ polymerization of 3-hexylthiophene within the mesopores of titania thin films to develop a titania-poly(3-hexylthiophene) (P3HT) hybrid films which can be used for an efficient organic-inorganic hybrid bulk heterojunction solar cell.  The titania films are formed by surfactant templating using Pluronic surfactants and have orthogonally tilted hexagonal close-packed cylindrical pores.  Such an architecture has been hypothesized by McGehee and coworkers to be ideal for organic / titania hybrid solar cells due to enhanced hole conductivity of P3HT confined in cylindrical channels.  The in-situ growth of P3HT is hypothesized to provide better heterojunctions than spin coating of P3HT onto titania because the thiophene monomers can penetrate titania pores more easily compared to the long polymers.  Also, the P3HT polymerization begins with a layer of grafted monomer, thus providing intimate contact between the polymer and the titania.  Two different approaches have been used for in-situ P3HT growth. In the first approach, the in-situ polymerization of P3HT on the surface of titania is carried out by using FeCl₃ as catalyst. Grafting of the polymers to titania is accomplished by adding 2-thiophenecarboxylic acid as a functional monomer that forms complexes with titanium at the pore surface.  In the second approach, we use silanization of titania surface using 3-aminopropyltriethoxysilane to provide covalent linkages of 3-hexylthiophene polymers onto titania. The biggest challenge is to control the selective growth of titania within the pores rather than at the external surface of the films.  This challenge can be overcome by using oxidation at the top surface (e.g. with UV/ozone cleaning) to remove functional monomers from the external surface to favor grafting only to the pore interior. The P3HT infiltration into the pores will be characterized by UV-vis spectroscopy, infrared spectroscopy, energy dispersive x-ray spectroscopy and scanning electron microscopy. Once we confirm that we have selectively grown P3HT within the pores of titania, we will discuss the photovoltaic properties of these films and compare the performance with the films prepared by spin coated regioregular P3HT onto titania.