Design of Ferroelectric Double Perovskite Oxides as Photovoltaic Materials

In ferroelectric-based photovoltaic materials, spontaneous polarization is expected to couple with the electronic and optical properties of the materials, and such materials have drawn attention as photovoltaic solar cells. Here, we utilize hybrid improper ferroelectricity to induce ferroelectric polarization in selected A-site layered and B-site rock-salt AA′BB′O 6 double perovskites and propose an alternate route to design ferroelectric photovoltaic semiconductors. First-principles density functional theory calculations and ab initio molecular dynamics simulations are performed to investigate the optical, electronic, and ferroelectric properties. We consider RbLaMnWO 6 and RbYMnWO 6 as model systems to pursue this study. We identify that these materials are semiconductors with a minimalist forbidden energy gap ( E g ) of 2.31 and 2.14 eV, respectively. This facilitates their absorption within the visible light region, thus enabling them to be exploited for optical device applications. The optical transition occurring in RbLaMnWO 6 reveals the relationship between the absorption spectrum and its electronic structure. We notice a low ferroelectric switching barrier in the case of RbLaMnWO 6, whereas a low band gap is espied in RbYMnWO 6 . To utilize the large visible spectra, we lower the band gap of RbYMnWO 6 from 2.14 to 1.67 eV by strain engineering. Similar structural, electronic, and optical properties are obtained for A-site substitution (A = K, Na). Further, molecular dynamics simulations show a polarization switching occurring at a temperature ( T ) of ∼400 K in RbLaMnWO 6 . This, in turn, enhances the dielectric response of RbLaMnWO 6 during switching and can be a potential candidate for designing optoelectronic materials where the structure–property relation can be controlled by electric field and/or temperature.