Exploring the Optoelectrical Parameters of Natural Dyes as Potential Cost-Effective Light Harvesting Materials for Dye-Sensitized Solar Cells

Cost reduction in Dye-Sensitized Solar Cells (DSSCs) can be realized by selecting sustainable components and exploring low-cost alternatives, such as natural dyes to synthetic counterparts. This study investigates the optoelectrical potential of five ethanol-extracted natural dyes namely, Bougainvillea, Euphorbia, Verbesina, and two Rosa variants (pink and red) as potential sensitizers for eco-friendly DSSC development. Ethanol was selected as the extraction solvent due to its availability, low toxicity, and balanced polarity, enabling effective isolation of both polar anthocyanins and nonpolar chlorophyll-like compounds from the plant material. Optical properties of the dyes, including absorbance, optical band gap, dielectric constant, and optical conductivity were evaluated via UV-Vis and FTIR spectroscopy. The synthesized dyes demonstrated prominent absorption peaks in the visible region, with Verbesina exhibiting the highest absorbance and light harvesting efficiency (LHE). The optical band gaps ranged from 2.4 eV to 3.0 eV, slightly larger than optimal for peak solar absorption indicating favourable π–π* transitions and good photostability. DSSCs fabricated with the dyes yielded power conversion efficiencies (PCE) between 0.01% and 0.13% which remain below the state-of-the-art benchmarks, however, performance indicators support their viability: Rosa (Pink) and Euphorbia demonstrated high open-circuit voltages (up to 0.31 V), and their FTIR spectra revealed strong vibrational bonding with TiO₂, suggesting enhanced interfacial adhesion and dye loading stability. Cyclic Voltammetry analysis provided key insights into the dye energetics and charge-transfer dynamics. All dyes exhibited HOMO/LUMO alignment compatible with TiO₂ conduction band and the I⁻/I₃⁻ redox mediator. Notably, Rose (Pink) and Euphorbia showed the most negative HOMO levels (–5.63 eV), correlating with enhanced electron-donating ability and favorable regeneration driving forces (~0.83 eV), while Bougainvillea exhibited superior anodic transfer kinetics in ln(I) vs √v analysis. Collectively, these findings highlight the potential of optimizing natural dye chemistry and device interfaces to bridge the performance gap with conventional DSSC technologies.