Defect-Induced Control on Current Conduction of Cobalt-Doped BiFeO 3 Thin-Film Devices

We report investigations of the optical band gap and the current conduction in cobalt-doped BiFeO 3 (BFO)-based thin film devices. It is widely believed that oxygen vacancies play a significant role in determining the current conduction in these devices. As the doping concentration of cobalt increased from 0 mol% to 10 mol%, the optical band gap of doped BiFe 1− x Co x O 3 ( x = 0.00, 0.03, 0.05, 0.10) decreased from 2.59 eV to 2.24 eV. However, the leakage current density was found to increase with cobalt doping. The J – V curve measured under dark conditions appeared linear from 0 to 2 V, indicating nearly ohmic conduction in these devices. The short-circuit current density, open-circuit voltage, fill factor, and photovoltaic efficiency of these Co-doped BFO (for 10 mol%) devices were found to be 9.3 × 10 −4 A/cm 2 , 0.72 V, 32%, and 0.22%, respectively. The photovoltaic efficiency of undoped BFO was found to be better than Co-doped BFO, even though Co doping reduced the optical band gap.