Fabrication and characterization of dye sensitized solar cells using natural dyes

Abstract

This work concerns the fabrication and characterization of DSSCs for photovoltaic applications. The main objectives of this research are fabricate TiO2 photo anode with three different thicknesses (4.54µm, 7.12µm and 12.3µm), to extract three different organic dyes from natural sensitizers (sumac, humic acid and red onion), to fabricate CNT counter electrode and to assemble solar cells with three different configurations (ITO/TiO2-Sumac/CNT/ITO, ITO/TiO2-Humic Acid/CNT/ITO and ITO/TiO2-Red Onion/CNT/ITO) and to determine the cells photovoltaic properties. The photo anode was prepared from TiO2 paste and deposited on the ITO conductive glass by doctor blade method with different thicknesses. The energy gap of the TiO2 photo anode was determined by UV-VIS spectroscopy. SEM images of the TiO2 photo anode suggested that the optimum thickness of TiO2 photo anode was 7.12µm. The pH scale of the three different dyes were optimized by the light absorption spectra from UV-VIS spectroscopy. The optimized pH of sumac, humic acid and red onion were 2.5, 2.5 and 2 respectively. The TiO2 photo anodes were soaked overnight in the dye solutions for sensitization. The absorbtion spectra of the TiO2 photo anode were increased by 8.79%, 8.68% and 12.68% for sumac, humic acid and red onion dye solution after soaking in the dyes. The counter electrode was fabricated with carbon nanotube in powder form and deposited on ITO glass by doctor blade method. The SEM images of carbon nanotube counter electrode suggested that the average diameter of the CNT was between 13.20-18.22μm. Three types of cell with ITO/TiO2-Sumac/CNT/ITO, ITO/TiO2-Humic Acid/CNT/ITO and ITO/TiO2-Red Onion/CNT/ITO configurations were assembled by mounting the photo anode on the counter electrode and by injecting 2-3 drops of liquid lithium iodide electrolyte into the cell. The photovoltaic properties of the cells were determined by I-V characteristic curve. The best photovoltaic performance was determined by ITO/TiO2-Sumac/CNT/ITO cell with 0.663V open circuit voltage (Voc), 4.64mAcm-2 short circuit current density, 0.637 fill factor and 1.96% efficiency. ITO/TiO2-Humic Acid/CNT/ITO cell provided 0.568V open circuit voltage (Voc), 5.86mAcm-2 short circuit current density, 0.563 fill factor and 1.87% efficiency. ITO/TiO2-Red Onion/CNT/ITO cell provided 0.445V open circuit voltage (Voc), 5.3mAcm-2 short circuit current density, 0.67 fill factor and 1.58% efficiency.