Performance Improvement Effect of an Inserted Sulfur-Doped Carbon Quantum Dots Layer on Organic Solar Cells

Poly(3-hexylthiophene) (P3HT) and phenyl-C61-butyric acid methyl ester (PCBM) based organic solar cells (OSCs) were fabricated and modified with a sulfur-doped carbon quantum dot (S-CQDs) inserted layer on top of the photoactive layer to investigate its effect on devices performance. The surface-engineered S-CQDs synthesized showed strong blue photoluminescence and enhanced UV-vis absorbance in the short-wavelength region, attributed to surface state transitions and band-gap modulation. The results revealed that the light harvesting capabilities were increased by the introduction of the S-CQD layer. Particularly below 450 nm, the absorbance profile broadened without disrupting the characteristic vibronic features of P3HT. The device characterization results demonstrated that an improvement in PCE from 1.76% to 3.07% was achieved owing to improved current density (J SC) and fill factor (FF). With the improved charge extraction and better energy-level alignment at the interface, the increased shunt resistance (R sh) and reduced series resistance (R s) led to an improved FF. Overall, the inserted S-CQDs layer effectively enhanced the optical and electronic properties of the OSCs fabricated, highlighting their potential as an electron transport layer in next-generation organic electronics.