The effect of defects induced by polarization on bandgap evolution and photovoltaic performance in KN-based semiconducting ferroelectric ceramics

The high-field polarization enables bandgap-engineered ferroelectric perovskite oxides to further enhance their photovoltaic performance. However, research on the mechanism of the high-field polarization-enhanced ferroelectric photovoltaic effect lacks understanding in terms of bandgap evolution. In this work, the ceramics [KNbO3]1−x−[SrNi0.5Hf0.5O3−δ]x(KNSNH100x, x = 0.02 − 0.08), prepared by the solid phase method, exhibit good ferroelectricity and four absorption bandgaps, three of which have sub-bandgaps generated by Ni. The effect of increased defects induced by high-field polarization on bandgap evolution and photovoltaic properties was investigated. The increase in defect concentration in KNSNH2 induced by high-field polarization is the cause of the variation in bandgap structure in KNSNH2. Structural refinement suggests that the change in the bandgap after polarization can be induced by the lattice distortion. The evolution of bandgap structure after polarization in KNSNH2 lead to an enhancement of visible light absorption, which further improve the photovoltaic performance by produced more carriers. A two-fold enhancement of short-circuit photocurrent density (Jsc) under simulated solar irradiation is achieved in the KNSNH2 sample by polarization. This work provides new insights into the effect of defect induced by polarization on enhancing ferroelectric photovoltaic performance and the mechanism of bandgap evolution.