A bandgap-tunable KNbO 3 ferroelectric ceramic was prepared by introducing Bi/Co ion. The existence of mixed valence states of Co 2+ /Co 3+ in the system induced the bandgap reduction and its tunable behavior. KNbO 3 -BiCoO 3 solid solutions showed a typical orthogonal perovskite structure and maintained good ferroelectricity (P s = 15.13 µC/cm 2 ) and high-field polarization ability. The devices based on the .98KNbO 3 -.02BiCoO 3 sample exhibited an improved shortcircuit photocurrent density (J sc ) of 19.2 nA/cm 2 under simulated solar radiation, and this was further enhanced to 79.8 nA/cm 2 after a 60-kV/cm polarizing. The structural analysis of the samples after polarization reveals the effect of ferroelectric polarization on photovoltaic performance. This work provides new insights into the effects of ferroelectric polarization on photovoltaic performance.

Polarization is one of the unique properties of ferroelectric materials; yet the polarization mechanism for enhancing ferroelectric photovoltaic performance is rarely been investigated, particularly in terms of bandgap variation. In this work, the effect of high-field polarization on the enhanced photovoltaic performance of a ferroelectric ceramic, 0.98KNbO 3 -0.02SrCo 0.5 Hf 0.5 O 3−δ (KNSCH2), was explored in terms of bandgap variation. The bandgap of the KNSCH2 sample shrank after polarization because of the increase in potential energy band overlap and the upward shift of the valence band due to increased oxygen-vacancy defects. The polarization optimized the energy band structure of KNSCH2, promoting the separation and transport of photoinduced carriers and thus further enhancing its photovoltaic performance. The KNSCH2 sample shows a twofold enhancement in J sc after 60 kV/cm polarization. The degree of the lattice distortion of KNSNH2 increased following polarization, causing a minute increase in its cell asymmetry. The reasons for the bandgap narrowing and the creation of sub-bandgaps in the KNSCH samples were also investigated. This work opened new doors to understanding the mechanisms underlying the polarization-enhanced photovoltaic performance of ferroelectric materials.