Sustainable management of PET waste via oxygen plasma-enriched PET/rGO/TiO₂ counter electrodes in DSSCs

The sustainable valorization of plastic waste into energy-conversion devices presents an urgent research frontier in circular materials engineering. This study introduces, for the first time, oxygen plasma-enriched PET/rGO/TiO₂ (PGT) counter electrodes (CEs) derived from recycled polyethylene terephthalate (PET) waste for dye-sensitized solar cells (DSSCs). Five PGT composites (PGT0-PGT12) were fabricated under systematically varied plasma exposure times (0-12 min) to tune surface chemistry, roughness, and wettability. Oxygen plasma treatment imparted dual effects of chemical functionalization and nanoscale texturing, markedly enhancing electrocatalytic activity and interfacial charge transport. Structural, morphological, and spectroscopic analyses (SEM, FTIR, XRD, contact angle, and EIS) confirmed progressive increases in porosity, surface adhesion, and conductivity, accompanied by band-gap narrowing from 3.3 eV (PGT0) to 2.8 eV (PGT9). Photovoltaic measurements revealed significant improvements in power conversion efficiency (η), short-circuit current density (J_sc), and fill factor (FF), with PGT12 achieving η = 7.91 %, closely approaching the Pt benchmark (8.59 %). IPCE analysis demonstrated broadband enhancement in quantum efficiency, peaking at 82 % for PGT12, consistent with reduced charge-transfer resistance (R_ct) and improved electrolyte wetting. These findings establish oxygen plasma activation as a scalable and green route to transform PET waste into high-performance DSSC CEs. Beyond advancing DSSC technology, the strategy offers a generalizable platform for integrating recycled polymers into next-generation optoelectronic devices, aligning renewable energy production with sustainable waste management.