TiCl4/MgCl2 passivated TiO2 photoanodes sensitized with Dendrobium Sonia Orchid, Woodfordia fruiticosa, and Couroupita guianensis bio-photosensitizers for DSSC application

Abstract

The quest for sustainable and cost-effective photovoltaic (PV) technologies has driven the exploration of natural bio-photosensitizers in dye-sensitized solar cells (DSSCs). In this study, three novel flower-based dyes, Dendrobium Sonia Orchid (DS), Woodfordia fruiticosa (WF), and Couroupita guianensis (CG), were extracted using a Soxhlet extractor and employed in DSSCs with tailored TiO₂ nanorod (TNR) photoanodes. Among the three configurations, TiCl₄-treated TNRs (TC-TNRs) exhibited superior charge transport properties, with an electron diffusion length (L_e) of 22.82 mm, an electron diffusion coefficient (D_e) of 27.53 × 10⁻⁶ cm² s⁻¹, an electron lifetime (τ_e) of 1.15 s, a transport lifetime (τ_t) of 1.10 s, and a conductivity (σ) of 1.73 × 10⁻⁶ Ω cm⁻¹, resulting in an charge collection efficiency (η_cc) of 51.06%. A champion DSSC (FTO/TC-TNR/DS/(I⁻/I₃⁻)/carbon) gives the power conversion efficiency (PCE) of 0.73%, attributed to improved charge transfer and suppressed recombination. WF dye with TC-TNRs recorded the highest photocurrent density (J_SC) of 4.23 mA cm⁻², while CG dye with MC-TNRs exhibited the highest open circuit voltage (V_OC) of 501.61 mV. Despite promising results, efficiency remains limited, requiring enhancements in dye stability, light absorption, and charge transfer via molecular engineering, co-sensitization, and metal complexation. Optimizing surface passivation and electrolytes could further improve performance, paving the way for natural dyes in next-generation DSSCs, including flexible and semi-transparent photovoltaics.