Ferroelectric photovoltaic response engineered by lattice strain derived from local metal-ion dipoles

An unfavorable inverse relationship between polarization, bandgap, and leakage always limits the ferroelectric photovoltaic performances. This work proposes a strategy of lattice strain engineering different from traditional lattice distortion by introducing a (Mg_2/3Nb_1/3)³⁺ ion group into the B site of BiFeO₃ films to construct local metal-ion dipoles. A giant remanent polarization of 98 µC/cm², narrower bandgap of 2.56 eV, and the decreased leakage current by nearly two orders of magnitude are synchronously obtained in the BiFe_0.94(Mg_2/3Nb_1/3)_0.06O₃ film by engineering the lattice strain, breaking through the inverse relationship among these three. Thereby, the open-circuit voltage and the short-circuit current of the photovoltaic effect reach as high as 1.05 V and 2.17 µA /cm², respectively, showing an excellent photovoltaic response. This work provides an alternative strategy to enhance ferroelectric photovoltaic performances by lattice strain derived from local metal-ion dipoles.