Investigations on the effect of na ca and alum on tio2 nanorods for natural dye sensitized solar cells

Abstract

Dye sensitized solar cell (DSSC) is a photoelectrochemical cell. Unlike conventional solar cells it does not have a p-n junction rather a photoelectrode, electrolyte and counter electrode assembled in a sandwich structure. The photoelectrode is a mesoporous wide band gap semiconductor sensitized with dye. The electrolyte is a redox species that undergoes rapid oxidation and reduction. An inert, high catalytic metallic film is used as counter electrode. In general, the DSSC are prepared using synthetic dyes as sensitizer and TiO2 nanoparticle film as photoelectrode, which exhibits certain drawbacks. Efficiency and stability in longer run decides its significance in the market. They can be enhanced by improvising the characteristics and properties of the components in DSSC. Hence, in the present work, we have focused more on to the optimization of the structure of photoelectrode and stability of natural dye which may lead to better efficiency at lower outlay. The iodide /triiodide liquid electrolyte and platinum films were used as electrolyte and counter electrode respectively. Anthocyanins from natural dyes such as Caesalpinnia Pulcherrima (C.Pulcherrima) and Rose (Rosa) flowers are extracted and used as dyes for DSSC. The carboxyl groups present in anthocyanins shows a good anchoring property that enhances sensitization with the OH groups of TiO2 molecules. Rutile TiO2 nanorods prepared over FTO substrates by hydrothermal method is used as photoelectrode in DSSC. From the absorbance studies it was inferred that the TiO2 film shows a maximum peak at UV region with a band gap extracted from Tauc plot to be 3.1eV. The XRD spectrum of TiO2 film confirms the presence of pure rutile phase with good crystallinity. The EDAX studies shows the composition of Ti:O to be 55.27:36.07. FESEM shows the morphology of TiO2 nanorods of length ~2.4 µm arranged uniformly with an inclined angle shift. Each rod is made of small rods that combine to form a thicker one which was observed from the HRTEM images and the SAED pattern shows the lattice fringes with interplanar spacing d = 0.246 nm. Moreover the rod morphology persists at higher temperature and the properties of nanorods can be tuned by adding buffer layer, doping and etching. newline