Enhanced light harvesting in DSSCs using carbon dots derived from Alstonia venenata

This study presents a novel co-sensitization strategy utilizing carbon dots derived from Alstonia venenata in combination with the N719 dye to enhance the light-harvesting efficiency of dye-sensitized solar cells (DSSCs). The carbon dots were synthesized via a hydrothermal process using an aqueous extract of Alstonia venenata leaves, resulting in a material with broad absorption characteristics. These synthesized carbon dots were then drop-cast onto an N719-sensitized photoanode, leading to improved carrier generation and enhanced device performance. The selection of Alstonia venenata as a precursor is based on its rich phytochemical composition, which contains alkaloids, flavonoids, terpenoids and phenolic compounds that act as efficient carbon precursors and surface passivation agents. Upon carbonisation, these biomolecules yield functionally active carbon dots that can improve electron transport, minimise charge recombination and enhance dye anchoring at the TiO₂ surface. Carbon dots have demonstrated significant potential as co-sensitizers, offering a highly effective approach to increasing DSSC efficiency. Their strong binding affinity further facilitates efficient photoinduced electron transfer to the photoanode, contributing to improved device functionality. In this research, TiO₂ was employed as the photoanode, while N719 dye and carbon-dot-modified N719 served as sensitizers. Iodolyte HI-30 acted as the electrolyte, and Platisol T/sp functioned as the counter electrode. The unmodified DSSC exhibited a power conversion efficiency of 5.2%, which was enhanced to 6.0% with the incorporation of carbon dots as co-sensitizers. The significant efficiency improvement achieved through this co-sensitization strategy underscores the unique capabilities of carbon dots derived from Alstonia venenata, making this approach a promising advancement toward the development of cost-effective and high-performance DSSCs.