Photoresponse of KNbO3–AFeO3 (A = Bi3+ or La3+) ceramics and its relationship with bandgap narrowing

Abstract

The crystal structure of (1-x)KNbO3-xBiFeO3 (KNBF) and (1-x)KNbO3-LaFeO3 (KNLF) (where x=0.00; 0.01; 0.02; 0.04; 0.08; 0.16; 0.32) was evaluated by XRD and Raman spectroscopy. XRD data show the crystal symmetry to evolve from orthorhombic to tetragonal with increasing x. The optical bandgap was found to narrow systematically with increasing x. Raman spectroscopy analysis corroborated long-range polar order in all compositions. The photoresponse of x=0.32 shows a typical diode-like behaviour, with current and voltage of 0.115 µA and 0.075 V for KNBF and 0.19 µA and 0.035 V for KNLF, respectively. To our knowledge these represent the largest values among KNbO3-based ceramics, making them promising for photovoltaic applications.

Crystal Structure, Phase Transitions and Photoferroelectric Properties of KNbO3-Based Lead-Free Ferroelectric Ceramics: A Brief Review

“…Nevertheless, these Ni induced intermediate energy levels can enhance the overall optical absorption. Grinberg et al (2013) measured a modest short-circuit photocurrent, J sc , of 0.1 µA.cm −2 and open-circuit photovoltage, Subsequently, Elicker et al (2018) also found a similar degree of bandgap narrowing (i.e., a 0.9-1 eV) in the K 1−x La x Nb 1−x Fe x O 3 (KNLF) system, suggesting that the electronic lone-pair in Bi 3+ may play a negligible role in the physics of bandgap narrowing of KN, as shown on Table 5. These researchers fabricated FEPV devices from KNBF and KNLF (x = 0.32), which combined with a redox couple (I − /I 3− ) exhibited a typical diode-like behavior, showing J sc and V oc values of 0.115 µA and 0.075 V for KNBF and 0.19 µA (Grinberg et al, 2013) 3.1 (direct) (Zhou et al, 2014) BaCo 1/2 Nb 1/2 O 3−x (x = 0.4) 2.4 (direct) (Yu et al, 2016) BaCo 1/3 Nb 2/3 O 3 (x = 0.25) 2.44 (direct) (Si et al, 2018) BaNb 1/2 Fe 1/2 O 3−x (x = 0.1) 2.48 (direct) and 0.035 V for KNLF, respectively.…”

Achieving Ultrahigh Photocurrent Density of Mg/Mn-Modified KNbO3 Ferroelectric Semiconductors by Bandgap Engineering and Polarization Maintenance

“…Currently, most oxide ferroelectric ceramics manifest low J sc in the order of nA/cm 2 (1–200 nA/cm 2 ). A summary of the literature data for these systems is provided in Figure c. ,− Evidently, increasing the J sc of ferroelectric ceramics is critical for practical photovoltaic applications.…”

“…Schematic diagram of enhanced J sc of KN-based semiconducting ferroelectric ceramics through Mn/Mg modification, bandgap engineering, and high-field poling. Bandgaps of (a) pure KN and (b) (1 – x )­KN- x MM ( x = 0.02, 0.04, 0.06, and 0.08) ceramics; (c) comparison of J sc of unpoled/poled (1 – x )­KN- x MM samples with other perovskite oxide-based photovoltaic devices; − ,− , (d) ordered transformation of ferroelectric domains induced by high-field poling; and (e) steady-state photocurrent experiments of the poled/unpoled 0.94KN-0.06MM sample. Insets in (a) and (b) represent the P - E loops of pure KN and (1 – x )­KN- x MM ceramics, respectively.…”

Optical absorption by design in a ferroelectric: co-doping in BaTiO3

“…12 Similar reports of solid solutions of KNO with BaFe1/2Nb1/2O3, BaCo1/2Nb1/2O3-δ, BiYbO3, and LaFeO3 showed that the bandgap could be shifted down to 1.7 eV, 2.4 eV and 2.2 eV, 2.6 eV, respectively. [13][14][15][16] At last, several studies have focused on bandgap engineering by chemical substitution. Among those, reports on substitutions on the A-site of the perovskite showed a minor effect on the bandgap value.…”