Investigating the Influence of Red and Green Luminescent Carbon Quantum Dots Derived from Mangosteen Leaf Biomass on Enhanced Efficiency in Perovskite Solar Cells

The electron transport layer (ETL) is a crucial component of perovskite solar cells (PSCs). It facilitates electron transfer and minimizes recombination losses. Consequently, modifying the ETL can significantly enhance the overall power conversion efficiency of PSCs. In this work, carbon quantum dots (CQDs) were synthesized via a hydrothermal process using mangosteen leaf biomass. Ethanol and deionized water solutions were employed as solvents to fabricate red- and green-luminescent CQDs. The optimal fluorescent emission peaks of Red-CQDs and Green-CQDs are 679 and 507 nm, with average sizes of 6.99 ± 1.55 and 2.85 ± 0.29 nm, respectively. Green-CQDs have a high oxygen content, while Red-CQDs exhibit significant hydrogen bonding. A quantum confinement effect and different functional groups influence electronic energy band variations, resulting in distinct energy gaps of 1.80 eV for Red-CQDs and 3.17 eV for Green-CQDs. To enhance the performance of PSCs, CQDs were utilized as an interface modification layer between the ETL and perovskite layer. PSCs modified with Red-CQDs achieved 20.10% efficiency compared to 18.80% under control conditions. This improvement is attributed to enhanced charge extraction and reduced recombination losses, as confirmed by electrochemical impedance spectroscopy. These findings suggest that the surface modification with CQD layers significantly improves PSC efficiency.