Eco-engineered Fe₃O₄@cellulose@APTES nanocomposites as efficient dye-sensitized solar cell counter electrodes:...

This study examines whether environmentally friendly and cost-effective Fe₃O₄@natural-cellulose@APTES magnetic nanocomposites (MNCs) could be used as a new type of counter electrode in dye-sensitized solar cells (DSSCs). Using natural-cellulose as a renewable biopolymer makes the system more sustainable and brings good biocompatibility and a naturally active surface. Furthermore, coating the material with APTES (3-aminopropyltriethoxysilane) stabilises the surface and facilitates more efficient electron transfer. These features together make the proposed material a promising alternative worth exploring in DSSC applications. The MNCs were characterized using FTIR, SEM-EDS, XRD, BET, UV-Vis, VSM, TGA, XPS, and EIS. XPS analysis provided direct insight into the surface chemical states and confirmed that APTES functionalization subtly altered the local electronic environment, which plays a key role in facilitating interfacial charge transfer. Electrochemical impedance spectroscopy (EIS) results revealed that the Fe₃O₄@natural-cellulose@APTES MNCs exhibited multilayer dielectric behavior. Three distinct relaxation modes corresponding to charge transfer, grain boundary conductivity, and ionic migration processes were identified in the Nyquist plots at high, medium, and low frequency regions, respectively. The APTES coating significantly reduced the charge transfer resistance (R₁ ≈ 22.70 MΩ → R₁ ≈ 0.17 MΩ, as determined from fitting) and decreased the total relaxation time from the millisecond to the microsecond level. Furthermore, dielectric constant (ε') and loss factor (tan δ) analyses confirmed the presence of Maxwell-Wagner-type interface polarization and dipole resonance. Mott-Schottky measurements revealed that the Fe₃O₄@natural-cellulose@APTES MNCs exhibit n-type semiconductor characteristics with a carrier density of 6.5 × 10¹⁷ cm^-3. In DSSC performance tests, the APTES-modified electrodes exhibited significantly improved photovoltaic performance, with average values of Voc = 0.75 ± 0.02 V, Jsc = 12.12 ± 0.39 mA/cm², FF = 0.67 ± 0.01, and PCE = 5.90 ± 0.34%, while the highest efficiency reached 6.28%. These findings demonstrate that Fe₃O₄@natural-cellulose@APTES MNCs, with both high electronic conductivity and superior catalytic properties, represent a sustainable alternativeto platinum-based electrodes.