Optimizing the Ferroelectric Photovoltaic Performance of 0.9[KNbO ₃ ]–0.1[BaNi _1/2 Nb _1/2 O _3−δ ] Ceramics via Grain Size Engineering

This study elucidates the pivotal role of grain size engineering in enhancing the ferroelectric photovoltaic (FPV) performance of 0.9[KNbO3]–0.1[BaNi1/2Nb1/2O3−δ] [KBNNO] ceramics. A series of samples with grain sizes varying from 10 to 200 nm were synthesized via tailored sintering conditions. The grain growth significantly enhances ferroelectric polarization (from 12.45 to 26.50 μC/cm2) and increases the dielectric constant (from 1876 to ∼3974 at 1 Hz) while maintaining the band gap in the visible region of the solar spectrum. Concurrently, the reduction in the grain boundary density suppresses charge-carrier recombination and strengthens conductive pathways, as evidenced by the increase in the alternating-current conductivity (from 132 to 660 μS/cm). These improvements directly contribute to a superior photovoltaic performance, with the photocurrent density increasing from 26 to 60 μA/cm2, whereas the short-circuit current density increases from 5 to 9 μA/cm2. Further, the poling of KBNNO ceramics enhances the photoresponse of this material as the photocurrent density after the poling reached a maximum value of 101 μA/cm2 with a maximum short-circuit current density of 15.31 μA/cm2. Collectively, grain growth is a vital design parameter for optimizing the FPV performance and provides a comprehensive multiscale framework linking microstructural and functional properties in electroceramics.