Successive redox-mediated visible-light ferrophotovoltaics
Yuji Noguchi, Yuki Taniguchi, Ryotaro Inoue, Masaru Miyayama
Abstract
Abstract Titanium oxide materials have multiple functions such as photocatalytic and photovoltaic effects. Ferroelectrics provide access to light energy conversion that delivers above-bandgap voltages arising from spatial inversion symmetry breaking, whereas their wide bandgap leads to poor absorption of visible light. Bandgap narrowing offers a potential solution, but this material modification suppresses spontaneous polarization and, hence, sacrifices photovoltages. Here, we report successive-redox mediated ferrophotovoltaics that exhibit a robust visible-light response. Our single-crystal experiments and ab initio calculations, along with photo-luminescence analysis, demonstrate that divalent Fe 2+ and trivalent Fe 3+ coexisted in a prototypical ferroelectric barium titanate BaTiO 3 introduce donor and acceptor levels, respectively, and that two sequential Fe 3+ /Fe 2+ redox reactions enhance the photogenerated power not only under visible light but also at photon energies greater than the bandgap. Our approach opens a promising route to the visible-light activation of photovoltaics and, potentially, of photocatalysts.