Nano-structured TiO2 films by plasma electrolytic oxidation combined with chemical and thermal post-treatments of titanium, for dye-sensitised solar cell applications

This paper demonstrates a new method to grow nano-structured TiO2 over a plasma electrolytically oxidised titanium surface. Microstructural characterisation by employing a variety of transmission electron microscopy techniques was carried out to explore the nano-scale structural changes due to the alkaline and thermal treatments. Photovoltaic performance was measured and this revealed the effect of microstructural changes. Such coatings can be considered potential candidates for the electrode material in a dye-sensitised solar cell (DSSC). The experimental results show that a titania layer with a 3D network ‘nano-flaky’ surface can be successfully prepared. The obtained nano-flakes are around 100 to 200 nm across and have a thickness of less than 10 nm. These completely cover the outermost surface as well as the inner pores and voids. The formed nano-flaky structure is amorphous and provides a larger surface area for dye absorption to increase the efficiency of assembled DSSC. Thermal annealing treatment causes the transformation of the amorphous nano-flakes into anatase nano-crystallites and further enhances the photovoltaic efficiency of the assembled DSSC.