Photovoltaic effect in transition metal modified polycrystalline BiFeO3 thin films

In expensive clean and renewable energy materials are in immediate need for green energy applications. Among the various available energy sectors, the solar energy industry is one the fastest growing in the market for future generation energy needs. Particularly photovoltaic (PV) systems those directly convert the solar energy into electrical energy is are useful for solar energy development. The photovoltaic technologies have advanced for more than a century after the discovery of the photoelectric effect by Einstein. However, after decades of development, the commercialized crystalline silicon solar panels are still too expensive to compete with fossil energy. Photovoltaic (PV) devices provide a promising platform for harvesting solar energy to generate electricity and thereby contribute to environmentally safer fuel. In order to lower the energy harvesting costs, various photovoltaic cells such as thin as thin film amorphous silicon solar cells, copper indium gallium selenide solar cells, dye-sensitized solar cells, cadmium telluride solar cells, quantum dot solar cells, organic solar cells, perovskite solar cells etc. are under intense study. About a half century ago, the ferroelectric photovoltaic effect was discovered in a variety of ferroelectric materials in which a steady photovoltaic response (photovoltage and photocurrent) can be generated along the polarization direction. Generally, the ferroelectric photovoltaic effect originates from the spontaneous electric polarization in ferroelectric materials. The photovoltaic effect in ferroelectric thin films has attracted considerable interest to fulfill this requirement. Unlike the photovoltaic effect observed in a semiconductor p-n junction, the photovoltaic effect in ferroelectrics does not require an asymmetric interface and photo-voltage is not limited by the band gap of the material. Non-centrosymmetry in the unit cell might be the reason for photovoltaic effect in ferroelectric materials, which gives rise to asymmetries in electron excitation, relaxation, and scattering processes. The photovoltaic effect in ferroelectric materials is relied on the polarization-induced internal electric field.  Polarization mediated photovoltaic properties in BiFeO₃ thin films have been reported by several research groups. By suitable site engineering at Bi and Fe-sites, one can observe improvement ferroelectric photovoltaic properties by suppressing the significant leakage current behavior.  Transition metal modified polycrystalline BiFeO₃ (BFO) thin films with significant PV response is observed under illumination both in sandwich and lateral electrode configurations. Photovoltaic behavior was demonstrated in Bi_0.9Sm_0.1Fe_0.95Co_0.05O₃ (BSFCO) thin films under illumination in sandwich electrode configuration for both polarizations up state and down state. Large open-circuit voltage (Voc)~0.9V and with a small short-circuit current (Jsc) ~ −0.051μAcm⁻² for the polarization up state by applying a positive voltage pulse is obtained for these  Bi_0.9Sm_0.1Fe_0.95Co_0.05O₃ (BSFCO) films.