The effect of various plant extracts on TiO₂ nanoparticles as efficient photoanode materials for natural dye-sensitized solar cell applications: Green sol-gel and a comparative study

Abstract

The excessive use of fossil fuels significantly contributes to global warming and environmental damage. A viable solution to these problems is the use of renewable energy sources, especially the clean-energy potential of solar cells. This study investigates the photovoltaic properties of TiO₂ nanoparticles (NPs) combined with three specific natural dyes for dye-sensitized solar cells (DSSCs). TiO₂ NPs were synthesized via a green sol-gel method using Aloe vera extract as a natural reducing and stabilizing agent. The materials were analyzed using XRD, FTIR, FESEM, EDX, Raman, and DRS to investigate its crystal phase, morphology, and optical properties. The results show that the material has a crystallite size of ~17 nm and a band gap of 3.1 eV, making it suitable for efficient light harvesting. Thin films of TiO₂ were deposited on FTO substrates through spin coating, resulting in uniform and compact photoanodes that are favorable for dye adsorption. Platinum-coated FTO served as the counter electrode, ensuring high electrocatalytic activity. The assembled DSSCs utilized an iodide/triiodide redox electrolyte in ethylene glycol and were tested under standard AM 1.5 G illumination (100 mW/cm²). Among the natural dyes tested, black mulberry demonstrated the highest power conversion efficiency (PCE) at approximately 1.3%, followed by wild raspberry at 0.7% and red mulberry at 0.3%. The good PCE of black mulberry can be partially attributed to the presence of anthocyanins, which serve as effective light-harvesting pigments, enhancing photon absorption and promoting the generation of charge carriers. The black mulberry device also showed higher FF (0.44) and Jsc (6 mA cm⁻²) compared with wild raspberry (0.41, 5.2 mA cm⁻²) and red mulberry (0.37, 4.6 mA cm⁻²), indicating more efficient electron injection and reduced recombination, which together lead to the improved PCE.