Correlation between the Acidity of Butterfly Pea (Clitoria ternatea L.) Flower Extract and Carbon Nanotube Counter Electrode Concentration on the Efficiency of Dye-Sensitized Solar Cells (DSSC)

In this research, we reported the fabrication of dye-sensitized solar cells (DSSC) using butterfly pea (Clitoria ternatea L.) flower extract as a natural sensitizer, TiO2 as the working electrode, carbon nanotubes (CNT) as the counter electrode, and a self-synthesized copper(I) thiocyanate (CuSCN) electrolyte. The extract was obtained by ultrasound-assisted extraction with methanol and adjusted to pH 2, 7 and 10, while the CNT concentration of the counter electrode was varied at 1, 2 and 3%. The anthocyanin content decreased from 23.75 mg/L at pH 2 to 11.19 mg/L at pH 10, and the extract absorbed visible light with a maximum at 550 nm. FTIR characterization showed O–H, C–H, C=C and C–O groups in the extract, together with Ti–O and In–O bands in the assembled photoanode, which indicates the interaction between the dye, TiO2 and ITO glass. The Tauc plot showed that the band gap energy decreased from 3.03 to 2.98 eV when CNT was added. The performance of the DSSC was tested using a digital multimeter under indoor light, a 20 W halogen lamp, and outdoor sunlight. The highest photovoltaic efficiency of 0.29% was obtained from the DSSC with the pH 2 extract and the 3% CNT counter electrode under sunlight. The efficiency increased as the dye became more acidic and as the CNT concentration increased.