Hybrid polymer/TiO2 films by in situ hydrolysis condensation of titanium alkoxide precursors for photovoltaic transparent windows

International audiencePoly(vinylcarbazole)/TiO2 hybrid thin films have been produced by the hydrolysis condensation of titanium alkoxide precursors dispersed in a polymer layer deposited on ITO substrates. Common alkoxide precursors like titanium isopropoxide [Ti((OPr)-O-i)(4)] show a fast hydrolysis beginning during film deposition, which leads to early phase separation. A new TiO2 precursor precursor bearing carbazole groups: titanium tetrakis 9H-carbazole-9-yl-ethyl-oxy [Ti(OeCarb)(4)] has been used to slow down the reactivity of the precursor by a steric hindrance effect. Improved precursor dispersion in the polymer solution is obtained for this new precursor leading to an homogeneous dispersion of the TiO2 phase at the nanoscale in the hybrid film. Rutherford Backscattering Spectrometry has shown that the hydrolysis condensation was effective with the production of carbazol alcohol remaining trapped in the bulk of the film. This residual alcohol leads to an increase of the UV optical absorption of the PVK/TiO2 hybrid films. Improvement of the balance between the two types of photogenerated charges has been shown by surface potential decay experiments upon the formation of a TiO2 conduction network for the transport of electrons. The film is almost transparent above 350 nm opening a new route for the elaboration of semi-transparent photovoltaic glasses, which can find application on the growing market of energy efficient buildings