Switchable Photovoltaic Effects in Hexagonal Manganite Thin Films Having Narrow Band Gaps

Ferroelectric photovoltaics (FPVs) are being extensively studied owing to their anomalously high photovoltages, coupled with reversibly switchable photocurrents. However, FPVs suffer from their extremely low photocurrents, which is primarily due to their wide band gaps. Herein, we present a new class of FPV by demonstrating (i) a nearly optimum band gap of similar to 1.55 eV and (ii) the ferroelectric polarization switching in the epitaxial hexagonal manganite thin films, h-RMnO3, where R = Lu and Y. According to the thickness-dependent photovoltaic measurements, the ITO/h-LuMnO3/Pt solar cell shows a power conversion efficiency of similar to 0.11% when the thickness of the h-LuMnO3 layer is similar to 150 nm. We have shown that the PCE is 1-3 orders higher than those of classical FPVs such as undoped Pb(Zr,Ti)O-3 and BiFeO3 under the standard AM 1.5G illumination. We have further elucidated that the switchable photovoltaic effect dominates over the nonferroelectric internal field effect.