Comparison of photostability, optical and structural properties of TiO2/conjugated polymer hybrid composites prepared via different methods

In this work, we have synthesized high quality TiO2 nanocrystallites by sol-gel method (TiO2 white (w)) and compared its properties with the ones synthesized by the simple hydrolysis method in aqueous solution (TiO2 transparent (t)). The TiO2/MEH-PPV nanocomposites are formed mainly by two ways: (i) Prepared in the form of the colloidal solution by adding the known concentration of the TiO2 in MEH-PPV and then sonicate it well; (ii) In the thin film form by depositing the above solution over a glass substrate by spin coating. The properties of the resulting dispersions could be tailored by varying the composition and concentration of TiO2 nanoparticles in CP's. The TiO2 nanoparticles prepared by both methods show anatase character of TiO2 as elucidated by X-ray diffraction (XRD) studies. Transmission electron microscopic (TEM) studies reveal that the transparent colloidal suspension of TiO2 exhibits agglomeration of TiO2 nanoparticles (size ∼ 150-300 nm) and this trend is maintained in the MEH-PPV matrix for TiO2/MEH-PPV composites as well. However, the composite obtained by mixing MEH-PPV with sol-gel prepared TiO2(w) shows uniform nanoscale dispersion of TiO2 (size ∼ 20 nm) in MEH-PPV matrix. The UV-VIS absorption, photoluminescence (PL) and lifetime studies confirm the presence of dynamic quenching effect indicating efficient photoinduced charge transfer in TiO2/MEH-PPV hybrid composites particularly with white TiO2. It is conjectured that the devices containing TiO2/MEH-PPV composites for TiO2 prepared by the sol-gel method should lead to significant improvement in the photovoltaic performance of TiO2/MEH-PPV hybrid solar cells.