Design of Ferroelectric Double Perovskite Oxides as Photovoltaic Materials

Inferroelectric-based photovoltaic materials, spontaneous polarizationis expected to couple with the electronic and optical properties ofthe materials, and such materials have drawn attention as photovoltaicsolar cells. Here, we utilize hybrid improper ferroelectricity toinduce ferroelectric polarization in selected A-site layered and B-siterock-salt AA & PRIME;BB & PRIME;O-6 double perovskites andpropose an alternate route to design ferroelectric photovoltaic semiconductors.First-principles density functional theory calculations and ab initio molecular dynamics simulations are performed toinvestigate the optical, electronic, and ferroelectric properties.We consider RbLaMnWO6 and RbYMnWO6 as modelsystems to pursue this study. We identify that these materials aresemiconductors with a minimalist forbidden energy gap (E (g)) of 2.31 and 2.14 eV, respectively. This facilitatestheir absorption within the visible light region, thus enabling themto be exploited for optical device applications. The optical transitionoccurring in RbLaMnWO6 reveals the relationship betweenthe absorption spectrum and its electronic structure. We notice alow ferroelectric switching barrier in the case of RbLaMnWO6, whereas a low band gap is espied in RbYMnWO6. To utilizethe large visible spectra, we lower the band gap of RbYMnWO6 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 polarizationswitching occurring at a temperature (T) of & SIM;400K in RbLaMnWO6. This, in turn, enhances the dielectricresponse of RbLaMnWO6 during switching and can be a potentialcandidate for designing optoelectronic materials where the structure-propertyrelation can be controlled by electric field and/or temperature.