Synergistic enhancement of quasi-solid-state dye-sensitized solar cells using carotenoids and santalin as co-sensitizers

Abstract Co-sensitization in quasi-solid-state dye-sensitized solar cells (DSSCs) is a promising strategy to broaden light absorption, enhance electron injection, and suppress recombination, thereby improving overall device efficiency. This study investigates natural dyes extracted from Sea buckthorn berries (SBT) and Red sandalwood (RSW) as mono- sensitizers and co-sensitizers in DSSCs employing a polymer-in-salt electrolyte. TiO 2 photoanodes sensitized with these dyes were characterized using XRD, FTIR, UV-Vis spectroscopy, and FESEM to analyze crystallinity, functional groups, morphology, and optical properties. Photovoltaic performance was evaluated using current density–voltage (J–V) measurements with statistical validation ( n = 5 devices per condition; mean ± SD; ANOVA–Tukey’s HSD post hoc analysis) confirming reproducibility, while the apparent series resistance (R s ) and shunt resistance (R sh ) were extracted from the J–V characteristics as lumped electrical parameters. These parameters are considered supporting electrical characteristics of the fabricated devices rather than direct measures of interfacial charge-transfer resistance or recombination kinetics. Under standardized sensitization conditions, the co-sensitized devices exhibited improved photovoltaic performance compared with the corresponding mono-sensitized cells. Among the investigated devices, the optimized co-sensitized photoanode containing 25% SBT and 75% RSW exhibited the highest power conversion efficiency (η) of 1.20%, with a short-circuit current density (J sc ) of 5.00 mA/cm 2 , open-circuit voltage (V oc ) of 447 mV, and fill factor (FF) of 0.51. This enhanced performance was accompanied by the lowest apparent series resistance (R s = 163.3 Ω) and highest apparent shunt resistance (R sh = 10591Ω) among all tested cells. In comparison, mono-sensitized SBT and RSW devices achieved efficiencies of 0.46% and 0.93%, respectively, with apparent R s values of 413.8 Ω and 199.7 Ω. The improved photovoltaic response of the 25:75 SBT/RSW device is consistent with the complementary optical characteristics of the two sensitizers and their possible combined contribution to light harvesting and photovoltaic response. The relatively small variations observed in J sc , V oc , FF, η, R s , and R sh indicate good device reproducibility among the tested devices, with variation within approximately 5–10% for most parameters. The results demonstrate the potential of SBT/RSW co-sensitization as an environmentally compatible approach for improving the photovoltaic performance of quasi-solid-state DSSCs and provide a basis for further mechanistic investigation using EIS, IPCE, and quantitative dye-loading measurements on freshly fabricated devices. These findings highlight the potential of crude plant-derived co-sensitizers for eco-friendly, efficient DSSC development.