Enhanced photovoltaic performance via polarization in Bi/Co co‐doped KN‐based ferroelectric ceramics

Abstract

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.

Microstructures and photovoltaic effect of KNbO3–SrCo0.5Hf0.5O3−δ ferroelectric semiconductors

“…The average grain sizes of the samples were 5.53, 0.20, 0.16, 0.17, and 0.17 µm, respectively, as shown in Figure S5C. Grain refinement of the sample can be interpreted as the formation of solid solution disrupting the ordering of the growth of the original KN crystal structure 22,52 . In addition, the presence of numerous oxygen vacancies conferred difficulty in the grains to grow into large grains 53 .…”

“…Grain refinement of the sample can be interpreted as the formation of solid solution disrupting the ordering of the growth of the original KN crystal structure. 22,52 In addition, the presence of numerous oxygen vacancies conferred difficulty in the grains to grow into large grains. 53 The backscattered electron picture and atomic percentage of KNSCH2 and EDS elemental surface distribution mapping are displayed in Figure S5D,E.…”

“…The majority of ABO 3 -type ferroelectric oxides have a wide bandgap due to the large electronegativity difference between the B-site ions and O-ions, 21,22 which results in their absorption of light being concentrated in the UV region (merely ∼8% of the solar spectrum), thereby exhibiting a lower photovoltaic response. The classical ferroelectric BiFeO 3 has received a lot of attention from researchers because of its relatively small bandgap value of 2.7 eV, 23 but it merely absorbs about 20% of the solar spectrum.…”

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

“…The J − V curves for KNBNH6 tested under the light power of 100 mW/cm 2 after 30 kV/cm positive and negative polarization for 30 min are shown in Figure 1G, which correspond to J sc values of 702.9 and −369.4 nA/cm 2 respectively. KNBNH6 has unequal absolute values of J sc after positive and negative polarization due to the inversion asymmetry of its cell structure and the difference in Schottky barriers at the interface between the ceramic and Ag and ITO electrodes 32,33 . The J − V curves of KNBNH6 after 30 min of polarization with different polarization fields tested under 100 mW/cm 2 light are shown in Figure 1H and their corresponding J sc values are shown in Figure 1I.…”

“…The average grain sizes of the samples are shown in Figure 7F, with the average grain sizes of 5.73, .21, .20, .21, and .17 μm respectively. This phenomenon can be interpreted as the dissolution of Ba, Hf, and Ni into the lattice of KN disrupting the long‐range orderly arrangement of its crystal growth and thus leading to grain refinement 32 . Accordingly, the oxygen vacancies produced by the designed composition can hinder the growth of grains into large size grains 52 .…”