Solution processed bismuth ferrite thin films for all-oxide solar photovoltaics

The present work delivers the first assessment of BiFeO₃ (BFO) thin films as an absorber for sustainable all-oxide photovoltaic devices. Films are deposited from a metal-organic precursor complex solution followed by annealing in air at 673 K for 2 h. X-ray diffraction, complemented by quantitative analysis, indicated formation of pure BFO with rhombohedral structure (R₃C). Atomic force microscopy suggests deposition of compact and smooth films with spherical particles of sizes ∼150 nm. A direct band gap of 2.2 eV is ascertained from UV-vis-NIR spectroscopy. Mechanistic aspects of the BFO formation are discussed based on thermograveminetric analysis, differential scanning calorimetry, and infrared spectroscopy of the precursor complex. A proof-of-concept BFO/ZnO heterojunction based solar cell fabricated by solution processing delivered a photoconversion efficiency of 3.98% with open-circuit voltage (V_oc), short-circuit current density, and fill factor of 642 mV, 12.47 mA/cm², and 50.4%, respectively. The device exhibits a maximum external quantum efficiency of nearly 70%. These parameters are among the highest values reported for all oxide PV. Analysis of the V_oc, series resistance, and conversion efficiency as a function of temperature revealed valuable information about recombination processes.