The need for ferroelectric materials with both narrow bandgaps (E_g) and large remanent polarization (P_r) remains a key challenge to the development of high-efficiency ferroelectric photovoltaic (FPV) devices. In this work, [(K_0.43Na_0.57)_0.94Li_0.06][(Nb_0.94Sb_0.06)_0.95Ta_0.05]O₃ (KNLNST)-based lead-free ceramics with narrow E_g and large P_r are obtained via Fe₂O₃ doping. By optimizing the level of Fe₂O₃ doping, a KNLNST+1.3% Fe₂O₃ ceramic is fabricated that simultaneously possesses a narrow E_g of 1.74 eV and a large P_r of 27.05 μC/cm². These values are much superior to those of undoped KNLNST ceramics (E_g = 3.1 eV and P_r = 17.73 μC/cm²). While the large P_r stems from the increment of the volume ratio between the orthorhombic and tetragonal phases (V_O/V_T) in KNLNST ceramics by proper amount of Fe³⁺ doping, the narrow E_g is attributed to the coupling interaction between the Fe³⁺ dopants and the B-site Sb³⁺ host ions. Moreover, a switchable photovoltaic effect caused by the ferroelectric depolarization electric field (E_dp) is observed in the KNLNST+1.3% Fe₂O₃ ceramic-based device. Thanks to the narrower E_g and larger P_r of the doped ceramic, the photovoltaic performance of the corresponding device (open-circuit voltage (V_oc) = −5.28 V and short-circuit current density (J_sc) = 0.051 μA/cm²) under a downward poling state is significantly superior to that of an undoped KNLNST-based device (V_oc = −0.46 V and J_sc = 0.039 μA/cm²). This work offers a feasible approach to developing ferroelectric materials with narrow bandgaps and large P_r for photovoltaic applications.

AgNbO₃ based antiferroelectric (AFE) ceramics have large maximum polarization and low remanent polarization, and thus are important candidates for fabricating dielectric capacitors. However, their energy storage performances have been still large difference with those of lead-based AFEs because of their room-temperature ferrielectric (FIE) behavior. In this study, novel La³⁺ and Ta⁵⁺ co-substituted AgNbO₃ ceramics are designed and developed. The introduction of La³⁺ and Ta⁵⁺ decreases the tolerance factor, reduces the polarizability of B-site cations and increases local structure heterogeneity of AgNbO₃, which enhance AFE phase stability and refine polarization-electric field (P–E) loops. Besides, adding La³⁺ and Ta⁵⁺ into AgNbO₃ ceramics causes the decrease of the grain sizes and the increase of the band gap, which contribute to increased E_b. As a consequence, a high recoverable energy density of 6.79 J/cm³ and large efficiency of 82.1%, which exceed those of many recently reported AgNbO₃ based ceramics in terms of overall energy storage properties, are obtained in (Ag_0.88La_0.04)(Nb_0.96Ta_0.04)O₃ ceramics. Furthermore, the discharge properties of the ceramic with discharge time of 16 ns and power density of 145.03 MW/cm³ outperform those of many lead-free dielectric ceramics.