Property Engineering of Cobalt-Doped Bismuth Ferrite Nanoparticles for Photovoltaic Energy Harvesting

This work provides an integrated, single-study assessment of how 10% cobalt substitution at the Fe (B) site engineers the structural, morphological, optical, and electrical properties of BiFeO₃ nanoparticles — properties that are typically reported in isolation across separate studies. Prepared under identical sol–gel and annealing conditions to enable direct comparison, pristine BFO and BFCO-10 are shown to retain the rhombohedral R3c perovskite framework (with only a trace Bi₂₅FeO₄₀ phase) while Co doping simultaneously contracts the unit cell, raises microstrain, and refines the crystallite size from 65.7 to 49 nm and the particle size from 170 to 128 nm (SEM). Most significantly, Co substitution narrows the direct optical band gap from 2.06 to 1.80 eV — extending visible-light absorption toward the photovoltaic-optimal range — while concurrently lowering AC resistivity and enhancing conductivity through defect-mediated (Fe²⁺/Fe³⁺, Co²⁺/Co³⁺) charge transport. The study’s contribution lies in linking these effects within one coherent structure–morphology–property framework, demonstrating that modest B-site Co doping is an effective single-dopant route to tailor BiFeO₃ for visible-light photovoltaic energy harvesting without disrupting the parent perovskite structure.