Mechanistic correlation between electron injection, recombination, and photovoltage in c ota tinctoria , punica granatum , and linaria grandiflora -based natural dye-sensitized solar cells

Abstract Natural dye-sensitized solar cells ( n -DSSCs) offer a sustainable and low-cost alternative to conventional photovoltaics. Three natural dyes - Cota tinctoria ( CTT ), Punica granatum ( PG ), and Linaria grandiflora ( LG ) - are investigated as a new eco-friendly sensitizer, and their photovoltaic performance is systematically correlated with energetic parameters. Comprehensive FT-IR, UV–vis, cyclic voltammetry (CV), and electrochemical impedance spectroscopy (EIS) analyses were employed to evaluate the relationships between electron injection driving force ( ΔG inj ), recombination resistance ( R rec ), and open-circuit voltage ( V OC ). Among the investigated natural dyes, the CTT -based device obtained the highest short-circuit current density ( J SC = 2.11 mA cm −2 ), open-circuit voltage ( V OC = 610 mV), and efficiency ( η = 0.91%). The correlation identified between ΔG inj , R rec , and V OC indicates that injection and recombination energies determine the efficiency of devices. These insights establish a mechanistic framework linking molecular energy alignment with photovoltaic behavior and guide the design of next-generation bio-derived sensitizers. Importantly, the study shows that superior ΔG inj facilitates stronger electron injection into TiO 2 , while higher R rec values suppress interfacial recombination, collectively governing V OC and overall efficiency. Overall, the results demonstrate that interplay between ΔG inj and R rec governs the photovoltaic behavior of natural dye-based DSSCs, establishing Cota tinctoria as a particularly promising bio-derived sensitizer for next-generation solar energy applications.