Toward an Enhanced Room-Temperature Photovoltaic Effect in Ferroelectric Bismuth and Iron Codoped BaTiO₃

Abstract

Ferroelectric (FE) materials usually possess very high band gap (∼3–4 eV) and extremely poor electrical conductivity, which renders them unsuitable for photovoltaic applications. Here, we demonstrate that a carefully designed Bi–Fe codoped BaTiO3 (BTO) system (Ba1–x Bi x Ti0.9Fe0.1O3−δ, 0 ≤ x ≤ 0.10) provides a unique platform with the simultaneous optimization of low band gap, high FE polarization, and reasonable conductivity. We, thereby, find that the Jahn–Teller distortion associated with the doped transition metal ions, tetragonality (c/a), and oxygen vacancy content lead to such a controlled tuning of optical band gap, FE polarization, and electrical conductivity, respectively, over a wide range. While x = 0.00 (only Fe-doped) stabilizes in the undesirable paraelectric-hexagonal phase, x = 0.02 (Bi–Fe codoped) is engineered to possess a low band gap (∼1.55 eV), high FE polarization (∼5.2 μC/cm2) due to significant recovery of the FE tetragonal phase by more than 60%, and reasonably high electrical conductivity compared to BaTiO3, which cause it to exhibit the largest photovoltaic response within the series. Such an approach of optimizing the desired physical properties in a closely related mixed phase material where the ferroelectricity is engineered in the majority tetragonal BTO phase, while the minority hexagonal BTO phase aids in the reasonable conductivity (a combination that is not realizable in usual single phase FE materials), along with an optimum band gap, is promising in the realization of many more potential FE-based photovoltaic materials.

Microscopic Insight into Structure Determination of Ferroelectric Photovoltaics in Aurivillius-Phase Ferroelectrics

“…The observed curves may be correlated with those of the single-damped harmonic oscillator. This mode is suitable for the Sr 1– x Ba x Bi 4 Ti 4 O 15 ( x = 0, 0.2, 0.5, 0.8, and 1.0) displacement ferroelectricity . The spectrum of dielectrics in Figure a is similar to the capacitance frequency spectrum of the displacement along the polar axis.…”

“…The resonant-type dispersion at 10 6 to 10 7 Hz is also associated with the ferroelectric soft mode . There is also a shoulder near 1 MHz, which is caused by intrinsic defects of Sr 1– x Ba x Ti 4 Bi 4 O 15 ( x = 0, 0.2, 0.5, 0.8, and 1.0) Figure b shows the Nyquist plot of impedance spectroscopy in the frequency range from 10 Hz to 100 MHz.…”

“…This mode is suitable for the Sr 1−x Ba x Bi 4 Ti 4 O 15 (x = 0, 0.2, 0.5, 0.8, and 1.0) displacement ferroelectricity. 21 The spectrum of dielectrics in Figure 4a is similar to the capacitance frequency spectrum of the displacement along the polar axis. The resonant-type dispersion at 10 6 to 10 7 Hz is also associated with the ferroelectric soft mode.…”

“…22 There is also a shoulder near 1 MHz, which is caused by intrinsic defects of Sr 1−x Ba x Ti 4 Bi 4 O 15 (x = 0, 0.2, 0.5, 0.8, and 1.0). 21 Figure 4b shows the Nyquist plot of impedance spectroscopy in the frequency range from 10 Hz to 100 MHz. Each one emerges as a large and small semicircle curve on the Nyquist graphics.…”

Ti3+ self-doping in BaTiO3 ceramic for multi-sensor applications: reduced bandgap with maintained ferroelectric properties

“…For example, Ce as a dopant on both Ba and Ti sites, Ru, Ni-Nb, Fe-Nb doped on the Ti site, as well as Bi and Fe co-doped on the Ba and Ti sites have been found to cause a significant reduction of ferroelectricity. 14,[40][41][42][43][44] Thus, it is challenging to reduce the bandgap meanwhile maintaining the ferroelectricity for BTO material. Additionally, piezoelectric and pyroelectric properties are always too weak to be reported for low bandgap BTO-based materials.…”