Bandgap tuning of samarium and cobalt co-doped bismuth ferrite nanoparticles

Abstract Silicon with its bandgap energy of 1.1 eV can convert one-third of solar energy for single layer junction semiconductor PV cells. However, maximum theoretical power conversion efficiency requires a bandage energy of 1.4 eV. Thus, scientific endeavor to find suitable functional PV materials has been progressing in full swing. In the realm of such efforts, perovskite BiFeO3 (BFO) is a prospective PV material, but it has an Eg of 2.67 eV. Thus, bandgap tuning of BFO by various dopants has given an impetus to researchers. In this context, samarium and cobalt co-doped BFO, Bi(1-y)SmyFe(1-x)CoxO3 (with y = 0 or 0.1 and x = 0, 0.05, 0.1 or 0.15) was synthesized by sol–gel method. The amorphous zero-gel powder thus obtained was annealed to get the crystalline phase. Rietveld refinement of X-ray diffraction (XRD) revealed the structural transformation from rhombohedral to orthorhombic symmetry in single-doped and co-doped BFO nanoparticles. Fe–O bond length and Fe–O–Fe bond angle were calculated from the reconstructed crystal structure using XRD CIF data. Field emission scanning electron microscopy and transmission electron microscopy were conducted to characterize microstructural features and exhibited the decreasing trend of particle size with increasing dopant concentration. Electric impedance was found to decrease from 28 to 9.6 MΩ at 200 Hz with an increasing doping level. The bandgap energy was estimated from diffuse reflectance data obtained from UV–Vis-NIR spectrophotometry and justified in light of photoluminescence measurement. A significant reduction in bandgap energy from 2.05 to 1.40 eV would shed some light on increasing solar cell efficiency using perovskite samarium and cobalt co-doped BFO based PV cells.