Unveiling Ionic Conductive Filaments Enhanced Photovoltaic Response Exceeding Ferroelectrics Dimensionality Limit

Abstract The ferroelectric photovoltaic effect is intrinsically limited by the dimensionality of samples. Ion‐ferroelectrics provide tunable avenues to engineer photovoltaic properties through external electric fields, forming ionic conductive filaments crucial for resistive switching. However, the correlation between these filaments and the associated ion‐photovoltaic behaviors requires exploration to activate strong photovoltaic response in bulk ferroelectric materials. In this study, the critical correlation between out‐of‐plane nanosized conductive filaments and photovoltaic activity in CuInP ₂ S ₆ is clarified, highlighting the pivotal role of Cu ⁺ ion conductive filaments in ion‐photovoltaics. Through thermally‐induced anisotropic spinodal decomposition, a periodic ferroelectric superlattice with a mixed‐phase CuInP ₂ S ₆ /In _4/3 P ₂ S ₆ structure is fabricated, achieving a significantly enhanced second‐order nonlinear polarizability of χ ⁽²⁾ ≈ 6.05 × 10 ⁻¹⁰ mV ⁻¹ . The thick superlattice flake facilitates the in‐plane formation of micron‐scale ionic conductive filaments and yields a giant planar ion‐photovoltaic response, with a photocurrent density of ≈40.6 mA cm ⁻² under µW‐level illumination, overcoming the limitation of ferroelectric dimensionality in bulk photovoltaic devices. The observed anisotropic photocurrents arise from the synergistic interaction between ion‐photovoltaic and junction photovoltaic mechanisms within a planar device architecture. These artificially‐induced ionic conductive filaments can be reconfigurable through conventional electrical poling, offering valuable insights for the development of high‐performance ferroelectric photovoltaic devices with multiple photovoltaic mechanisms.