Enhanced photovoltaic response in Mn-doped BiFeO3-based perovskite solar cells

Prospect of organic-inorganic lead-halide perovskites in solar cell application is limited by their notorious ambient instability vis-à-vis performance degradation and lead toxicity. Isoelectronic bismuth-based oxide perovskites with suitable optoelectronic properties could be plausible alternatives. Here we show that manganese-doping in bismuth ferrite (BiFeO3 or BFO) tailors the optoelectronic properties suitable for the absorber layer in a perovskite solar cell. We study the crystal structure, surface morphology, and optoelectronic properties of solution deposited thin films (thickness, 250‒350 nm) of pristine and Mn-doped BFO (BFMO) from the perspective of photovoltaic applications. Both the systems exhibit rhombohedral R3c symmetry, an optical absorption coefficient, ~105 cm-1 throughout the visible range, and a charge carrier concentration, ~1018-19 cm-3. Mn-doping demonstrates a small direct bandgap reduction in BFO from 2.6 eV to 2.5 eV. Ultraviolet photoelectron spectroscopy (UPS) measurement determines the positions of the band edges (valence band maximum and conduction band minimum), required for the selection of carrier transport layers. BFMO-based solar cell, FTO/SnO2/BFMO/Spiro-OMeTAD/Ag achieves a power conversion efficiency of 1.92 %, in contrast to negligible response in BFO-based device. We predict that BFMO with superior optoelectronic properties can manifest a significantly high conversion efficiency precise defect control.