Effect of defect-induced bandgap intermediate states on the photovoltaic performance of KN-based ferroelectric ceramics

The inversion asymmetry of polar crystals enables ferroelectric ceramics to possess unique physical properties, among which the anomalous photovoltaic effect drives their potential application in photovoltaic conversion. Semiconducting (1-x) KNbO3-xBaNi(.5)Hf(.5)O(3-)(& delta;) (KNBNH, x = 2, 4, 6, 8%) ferroelectric ceramics with enhanced photovoltaic performance were prepared by utilizing conventional solid-state sintering strategies. In these ceramics, the defect-induced bandgap intermediate state is derived from the 3d split state of Ni and plays a dominant role in lowering the bandgap of KN. The defective bandgap state induced by Ni in KNBNH promotes its absorption of light and the separation of photogenerated carriers, thus enhancing its photovoltaic response. The KNBNH6 shows a maximum value of 138.7 nA/cm(2) for short-circuit photocurrent density (J(sc)) among these ceramics, which is further enhanced to 702.9 nA/cm(2) after 30 kV/cm polarization. Structural investigations after polarization indicate that polarization induced lattice distortion in KNBNH6, leading to an increase in the polarity of its cells. This work provides an understanding of defect-induced bandgap states and high-field polarization to enhance ferroelectric photovoltaic properties.