Comparative Sol–Gel Synthesis Approaches for BiFeO₃ Nanoparticles for Photovoltaic Solar Cell Applications

Abstract

Multiferroic Bismuth Ferrite (BFO), characterized by a direct optical bandgap in the range of 2.2 to 2.7 eV, has emerged as a favorable material for next-generation Photovoltaic (PV) and optoelectronic applications. However, obtaining phase-pure BFO nanoparticles remains a substantial challenge because of the volatility of bismuth and the narrow thermodynamic stability window of the perovskite phase. In the present study, high-purity multiferroic BiFeO₃ nanoparticles were successfully synthesized via an energy-efficient, low-temperature sol–gel route employing two distinct approaches: General Sol-gel and Tuned Sol-gel synthesis. The precursor sol was carefully adjusted to a pH of 1–2 using NH₄OH, while ethylene glycol was applied as a chelating and polymerizing agent to ensure homogeneous complexation of Fe³⁺ and Bi³⁺ ions. Following gel formation, the dried intermediates were annealed at 600°C to achieve phase crystallization. A comprehensive investigation was conducted to evaluate how these synthesis pathways influence crystal purity, structural characteristics, and multiferroic behavior. UV–VIS–NIR spectroscopic analysis confirmed the presence of a direct optical bandgap, consistent with intrinsic BFO. X-ray Diffraction (XRD) results verified that all the samples were structured in a single-phase rhombohedral perovskite (space group R3c), while refinement of diffraction patterns provided detailed insight into crystallite size, microstrain, and structural order. The morphology, elemental distribution, and particle-size evolution were further observed using field-emission scanning electron microscopy furnished with energy-dispersive spectroscopy, confirming uniform particle formation and compositional accuracy. Comparative analysis of the two sol–gel techniques revealed that the Tuned Sol-gel method yielded BFO nanoparticles of superior phase purity and structural integrity, with fewer secondary phases than those produced by the General Sol-gel method. Overall, this study demonstrates that Tuned Sol-gel processing offers a more reliable pathway for fabricating high-quality BFO nanoparticles suitable for photovoltaic and multifunctional device applications.