Enhanced Photovoltaic Performance of Inverted Organic Solar Cells Using Carbon Quantum Dots as a Hole Transport Layer

Inverted organic solar cells (OSCs) often have hole extraction inefficiencies and interfacial recombination at the anode interface, resulting in considerable resistive losses and reduced power conversion efficiency (PCE). To tackle these issues, biomass-derived carbon quantum dots (CQDs) were employed as a hole transport layer (HTL) in inverted OSCs based on poly(3-hexylthiophene):[6,6]-phenyl-C 61 -butyric acid methyl ester (P3HT:PCBM) using a simple and solution-based method. The introduction of CQDs as HTL increased light absorption, enhanced surface smoothness and improved interfacial energy alignment. The PCE increased from 1.86% to 2.75% under AM1.5G 1-sun illumination, representing a 47.8% enhancement. The PCE increased from 3.67% to 5.70% when illuminated by white LEDs, representing a rise of 55.3%. The results indicate that CQDs effectively enhanced hole extraction and reduced interfacial recombination at the anode interface, hence improving photovoltaic performance under both indoor and outdoor lighting conditions. The results confirm that CQDs are a viable, economical, and environmentally sustainable HTL material for next-generation OSCs.