\(\hbox {Bi}_{(1-y)}\hbox {Sm}_{{y}}\hbox {FeO}_{{3}}\) as prospective photovoltaic materials

The bandgap energy ( $${E}_{\mathrm {g}}$$ ) of silicon-based photovoltaic (PV) cells is 1.1 eV, which limits its efficiency to 33.33%. Thus, the quest for alternative materials with maximum theoretical power conversion efficiencies (PCE) is growing in full swing within scientific community. Bismuth ferrite (BFO) is one of the promising candidates due to its tunable $${{E}}_{\mathrm {g}}$$ . For visible light with wavelength from 380 to 750 nm, $${{E}}_{\mathrm {g}}$$ falls within the range of 1.65–3.1 eV. The photons with wavelengths of higher than 464 nm ( $${{E}}_{\mathrm {g }}= 2.67$$  eV) constitute 80% of the solar spectrum, which cannot be absorbed by un-doped BFO. Thus, lowering the $${{E}}_{\mathrm {g}}$$ of BFO is a promising way to obtain higher PCE of PV cells to harvest a wide range of visible light spectrum. In this context, we have synthesized samarium (Sm)-doped $$\hbox {Bi}_{{(1-y)}}{\mathrm {Sm}}_{y} {\mathrm {FeO}}_{{3}}$$ ( $${y} = 0.05$$ , 0.1 and 0.15) multiferroic nanoparticles using sol–gel method. The evolution of phase from xerogel was thoroughly investigated by differential scanning calorimetry and a noticeable peak shift of $$7^{\circ }\hbox {C}$$ was observed due to Sm doping compared to un-doped counterpart. For crystallinity, xerogel powder was annealed at $$600^{\circ }\hbox {C}$$ . Rietveld refinement of X-ray diffraction data have confirmed rhombohedral crystal structure (R3c) of annealed samples and a substantial reduction of crystal size from 57.4 to 16 nm. For the first time, a total suppression of secondary phase was obtained in $$\hbox {Bi}_{{99.05}}{\mathrm {Sm}}_{{0.05}} {\mathrm {FeO}}_{{3}}$$ with only 5 (at.)% Sm addition. Fe–O–Fe bond angle was found to change significantly from 154.77 to $$158.84^\circ $$ and Fe–O bond length was found to be decreased along long axis and increased along short axis in Sm-doped samples. Field emission scanning electron microscopy demonstrated a reduction in particle size from 164 to 88 nm with increasing Sm-dopant concentration. The bandgap energy of un-doped and Sm-doped $$\hbox {BiFeO}_{{3}}$$ was calculated from measured diffused reflectance data using UV–Vis–NIR spectroscopy, the result has shown a reduction of bandgap in Sm-doped $$\hbox {BiFeO}_{{3}}$$ to 1.9 eV.