Nitrogen-doped TiO₂ nanoparticle-carbon nanofiber composites as a counter electrode for Pt-free dye-sensitized solar cells

Nitrogen-doped TiO₂ nanoparticle-carbon nanofiber (CNF) composites were synthesized using one-pot electrospinning. As the amount of nitrogen-doped TiO₂ nanoparticles in the composites was increased from 3.4 to 13.8 wt%, the electrochemical and photovoltaic properties in dye-sensitized solar cells (DSSCs) were evaluated. DSSCs fabricated with composites containing 13.8 wt% nitrogen-doped TiO₂ nanoparticles showed the highest current density (15.65 mA/cm²), highest fill factor (60.50%), and superb power-conversion efficiency (6.31%). These improved properties are the result of the rough surfaces of the CNFs that serve as sites for reduction of I₃^- ions and the existence of TiN phases in the composites that reduced charge transfer resistance.