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

ABSTRACT 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.