Abstract

We propose $B$-site ${\mathrm{Bi}}^{5+}$-doped ferroelectric perovskite materials as suitable candidates for the bulk photovoltaic effect and related solar applications. The low-lying $6s$ empty states of the electronegative Bi atom produce empty bands in the energy gap of the parent materials, effectively lowering the band gap by 1--2 eV, depending on the composition of the ferroelectric end member and the concentration of ${\mathrm{Bi}}^{5+}$ in the solid solution. The polarization decreases but survives upon doping, which enables the ``shift-current'' mechanism for photocurrent generation, while the decreased band gap allows absorption of much of the visible spectrum. The magnitude of shift-current response is calculated for $0.75{\mathrm{Pb}}_{2}{\mathrm{InNbO}}_{6}\text{\ensuremath{-}}0.25{\mathrm{Ba}}_{2}{\mathrm{InBiO}}_{6}$ (PIN-BIB) and $0.75{\mathrm{Pb}}_{2}{\mathrm{ScNbO}}_{6}\text{\ensuremath{-}}0.25{\mathrm{Ba}}_{2}{\mathrm{ScNbO}}_{6}$ (PSN-BSB) and is predicted to exceed the visible-light bulk photovoltaic response of all previously reported materials, including ${\mathrm{BiFeO}}_{3}$. Furthermore, the existence of their intermediate bands and multiple band gaps, combined with Fermi-level tuning by $A$-site co-doping, also allows for their potential application in traditional $p\ensuremath{-}n$ junction-based solar cells as broad-spectrum photoabsorbers.

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