Bandgap engineering of cobalt-doped bismuth ferrite nanoparticles for photovoltaic applications

The bandgap energy range of multiferroic bismuth ferrite is 2.2–2.7 eV, making it a promising candidate for photovoltaic (PV) applications. But its efficiency is still very low ($${<}2\%$$). This report thus focusses on the application of bismuth ferrite ($$\hbox {BFO})$$ engineered with cobalt (Co) doping and on the tuning of its bandgap energy ($$E_{\mathrm{g}}$$). $$\hbox {BiFeO}₃$$ is a unique multiferroic material that simultaneously displays both ferromagnetic and ferroelectric properties at room temperature. Co doped with pure $$\hbox {BiFeO}₃$$ ($$\hbox {BiFe}_{({1-x})}\hbox {Co}_{{x}}\hbox {O}₃$$; $$x = 0, 0.05$$, 0.1 and 0.15) was synthesized by the sol–gel method and annealed at $$600^\circ \hbox {C}$$. X-ray diffraction shows the well-arranged crystalline structure and peaks of pure and doped-$$\hbox {BiFeO}₃$$ nanoparticles. A suitable reduction of $$E_{\mathrm{g}}$$ has been observed for Co-doped $$\hbox {BiFeO}₃$$, which may be appropriate for the effective use in PV solar cells. Thermogravimetric analysis and differential scanning calorimetry were used to investigate the thermal decomposition character of the xerogel powder and the pattern of pure and doped $$\hbox {BiFeO}₃$$ phases. Field emission scanning electron microscopy images show the surface crystallography of pure and Co-doped $$\hbox {BiFeO}₃$$. Co-doped $$\hbox {BiFeO}₃$$ has considerably reduced the crystallite and particle size of the samples. We have calculated the $$E_{\mathrm{g}}$$ of pure and doped $$\hbox {BiFeO}₃$$ using a UV–Vis–NIR spectrophotometer and the results show the important reduction of $$E_{\mathrm{g}}$$ (1.60 eV) of the Co-doped samples, which may have potential applications in PV solar cells.