Studies on the characteristics of $$\hbox {TiO}_2$$ photoanode and flavanol pigment as a sensitiser for DSSC applications

Abstract

In the present work, dye-sensitised solar cell (DSSC) is fabricated using natural dye (Tecoma Stans)-sensitised $$\hbox {TiO}_{\mathrm {2\, }}$$ as the photoanode, platinum as the counter electrode and lithium iodide and iodine as the electrolyte. Initially, $$\hbox {TiO}_{\mathrm {2\, }}$$ nanoparticles are synthesised by the sol–gel technique using glacial acetic acid as the hydrolysing agent. The photoanodes are prepared by the Doctor Blade technique using the synthesised nanoparticles coated onto the fluorine-doped tin oxide (FTO) substrate and annealed at 400, 500 and $$600^{\circ }\hbox {C}$$ for 30 min. Structural analysis shows the anatase phase of the $$\hbox {TiO}_{\mathrm {2}}$$ thin film with a tetragonal crystal structure. The optical transmittance is found to be around 95% with an optical band gap close to 3.1 eV and increases with an increase in annealing temperature. From the PL emission spectra, the excitation of the titania band is observed. The pigment flavan-4-ol which acts as a sensitiser is extracted from Tecoma Stans flower. From the absorption study of the pigment, the active region of radiation and the band gap are found to be around 550 nm and 2 eV respectively. FTIR analysis of the pigment shows a stable structure similar to that of the prepared photoanodes. CV analysis of the sensitiser shows maximum oxidation within the active region. Field emission scanning electron microscope (FE-SEM) analysis shows that the prepared photoanode ( $$600^{\circ }\hbox {C}$$ ) has spherical shape. The overall photoconversion efficiency of Tecoma Stans-sensitised $$\hbox {TiO}_{\mathrm {2}}$$ photoanode is 0.4491%.