Performance Evaluation of Natural Dye-Sensitized Solar Cells: A Comparison of Density Functional Theory and Experimental Data on Chlorophyll, Anthocyanin, and Cocktail Dyes as Sensitizers

Dye-sensitized solar cells (DSSCs) have emerged as a promising third-generation photovoltaic technology due to their low-cost fabrication, flexibility, reduced energy payback time, and better performance under diffuse light conditions. Natural pigments offer an environmentally and economically superior alternative to traditional synthetic dyes, which often require a complex synthesis and can be toxic. In this study, we assessed the potential of natural dyes extracted from Syzygium cumini and Malva verticillata at two different pH levels as individual and cosensitizers in DSSCs. The characteristic properties such as absorption, size distribution, and emission of the pigments were studied by using various analytical techniques, including UV–vis spectroscopy, Fourier-transform infrared (FTIR), zeta potential measurement, and dynamic light scattering. This technique helped deposit a thin TiO2 layer uniformly on the substrate. Additionally, theoretical calculations using density functional theory (DFT) and time-dependent DFT were performed to investigate the electronic and optical properties of dyes. Following validation with experimental UV and FTIR data, the model was employed to predict other cell properties of chlorophyll b, anthocyanidin, and their cocktail and compared with experimental observations. The results indicated that mostly acidified dyes and their combinations exhibited improved light absorption capabilities, enhanced intramolecular charge transfer properties, a reduced energy gap, and increased JSC. Antho/Chl at pH 3 and Chl at pH 3 led to improved photovoltaic performance, as experimentally demonstrated. However, power conversion efficiencies of dyes were theoretically up to 60–63% greater than experimental results. Predictively, antho/Chl pH 3 displayed a higher power conversion efficiency of 4.22%, which is achieved with a VOC and a JSC of over 0.991 eV and 1.536 mA/cm2, respectively.