The composition and poling-dependent photovoltaic studies in ferroelectric (Bi_1−xSr_x)(Fe_1−xTi_x)O₃ thin films

The polycrystalline (Bi_1−xSr_x)(Fe_1−xTi_x)O₃ (x = 0.0, 0.05, 0.10, and 0.20) thin films were grown on Pt(111)/TiO₂/SiO₂/Si(100) substrates using chemical solution deposition technique. X-ray diffraction pattern revealed that pure BiFeO₃ film is crystallized in rhombohedrally distorted crystal structure. However, the patterns for doped samples displayed a mixed-phase (rhombohedral + tetragonal) structure. The Raman studies revealed the emergence of B mode related to the tetragonal phase along with the modes corresponding to the rhombohedral phase in doped systems. The photovoltaic studies displayed a large photovoltaic response for the parent compound with an open-circuit voltage of 0.47 V. However, it showed a decrease in the photovoltaic response with an increase in composition x. The composition-dependent photovoltaic response could be correlated to the evolution of tetragonal phase fractions and the polarization. Additionally, the poling-dependent photovoltaic studies revealed the dominant role played by the polarization in comparison with the interface Schottky effect. This work gives an improved understanding of the ferroelectric photovoltaic mechanism and, therefore, may offer guidelines to design and optimize photovoltaic materials.