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New high T(c) multiferroics KBiFe₂O₅ with narrow band gap and promising photovoltaic effect.

Zhang G, Wu H, Li G, Huang Q, Yang C, Huang F, Liao F, Lin J - Sci Rep (2013)

Bottom Line: Computational "materials genome" searches have predicted several exotic MO₆ FE with E(g) < 2.0 eV, all thus far unconfirmed because of synthesis difficulties.Here we report a new FE compound with MO₄ tetrahedral network, KBiFe₂O₅, which features narrow E(g) (1.6 eV), high Curie temperature (T(c) ~ 780 K) and robust magnetic and photoelectric activities.The high photovoltage (8.8 V) and photocurrent density (15 μA/cm²) were obtained, which is comparable to the reported BiFeO₃.

View Article: PubMed Central - PubMed

Affiliation: State Key Laboratory of Rare Earth Materials Chemistry and Applications, College of Chemistry and Molecular Engineering, Peking University, Beijing 100871, P.R. China.

ABSTRACT
Intrinsic polarization of ferroelectrics (FE) helps separate photon-generated charge carriers thus enhances photovoltaic effects. However, traditional FE with transition-metal cations (M) of d⁰ electron in MO₆ network typically has a band gap (E(g)) exceeding 3.0 eV. Although a smaller E(g) (2.6 eV) can be obtained in multiferroic BiFeO₃, the value is still too high for optimal solar energy applications. Computational "materials genome" searches have predicted several exotic MO₆ FE with E(g) < 2.0 eV, all thus far unconfirmed because of synthesis difficulties. Here we report a new FE compound with MO₄ tetrahedral network, KBiFe₂O₅, which features narrow E(g) (1.6 eV), high Curie temperature (T(c) ~ 780 K) and robust magnetic and photoelectric activities. The high photovoltage (8.8 V) and photocurrent density (15 μA/cm²) were obtained, which is comparable to the reported BiFeO₃. This finding may open a new avenue to discovering and designing optimal FE compounds for solar energy applications.

No MeSH data available.


Related in: MedlinePlus

Selection rules for ferroelectric photovoltaic materials.(a) Schematic illustration of mechanism for photovoltaic effect in ferroelectric materials. (b) Spectra of solar radiance and UV-Vis-near IR absorption of BiFeO3 and KBiFe2O5. (c) Maximum theoretical efficiency vs. band gap; AM1.5 illumination. (d) Schematic electronic DOS of Fe3+ in octahedral Oh and tetrahedral Td coordination.
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f1: Selection rules for ferroelectric photovoltaic materials.(a) Schematic illustration of mechanism for photovoltaic effect in ferroelectric materials. (b) Spectra of solar radiance and UV-Vis-near IR absorption of BiFeO3 and KBiFe2O5. (c) Maximum theoretical efficiency vs. band gap; AM1.5 illumination. (d) Schematic electronic DOS of Fe3+ in octahedral Oh and tetrahedral Td coordination.

Mentions: Photovoltaic effects in ferroelectrics (FE) have been studied for many decades123. Recently, the discovery of large photovoltages up to 15 V in multiferroic BiFeO3 films4 has drawn enormous attention to FE photovoltaics567. Different from traditional semiconductor solar cells, the photovoltaic effect in FE is relied on the polarization-induced internal electric field8910 (illustrated in Fig. 1a) instead of a p-n or Schottky junctions, which can not only improve the separation and migration of light-generated electron-hole pairs but also reduce the cost of cell fabrication. Moreover, the photo-induced voltages in multidomain ferroelectrics will not be limited to the Eg of light absorbers10 (see in Supplementary Fig. S1), superior to traditional semiconductor solar cells (<1 V). However, traditional FE are typically insulators of large band gaps (Eg) (supplementary Table S1) with rather limited light absorption and photocurrent, thus unsuitable for photovoltaic applications. Ideally, a photovoltaic material should have11 (1) a band gap of 1.0–1.8 eV matching the solar spectrum (Fig. 1b and 1c), (2) a large light absorption coefficient of ~104–105 cm−1 and (3) an intermediate carrier concentration of ~1015–1017 cm−3, in addition to being a polar material with a strong build-in electric field of ~104–105 V cm−1. Most FE fail to meet these requirements. For example, BiFeO3, which has attracted much recent attention412, features a relatively low solar cell efficiency (~ 3 × 10−3%) due to the relatively large band gap (2.6 eV)13 and the relatively high electrical resistance (~1010 Ω cm)14. Since light absorption and carrier concentrations are both band-gap dependent, small band gap polar materials are thus of great interest.


New high T(c) multiferroics KBiFe₂O₅ with narrow band gap and promising photovoltaic effect.

Zhang G, Wu H, Li G, Huang Q, Yang C, Huang F, Liao F, Lin J - Sci Rep (2013)

Selection rules for ferroelectric photovoltaic materials.(a) Schematic illustration of mechanism for photovoltaic effect in ferroelectric materials. (b) Spectra of solar radiance and UV-Vis-near IR absorption of BiFeO3 and KBiFe2O5. (c) Maximum theoretical efficiency vs. band gap; AM1.5 illumination. (d) Schematic electronic DOS of Fe3+ in octahedral Oh and tetrahedral Td coordination.
© Copyright Policy - open-access
Related In: Results  -  Collection

License
Show All Figures
getmorefigures.php?uid=PMC3569630&req=5

f1: Selection rules for ferroelectric photovoltaic materials.(a) Schematic illustration of mechanism for photovoltaic effect in ferroelectric materials. (b) Spectra of solar radiance and UV-Vis-near IR absorption of BiFeO3 and KBiFe2O5. (c) Maximum theoretical efficiency vs. band gap; AM1.5 illumination. (d) Schematic electronic DOS of Fe3+ in octahedral Oh and tetrahedral Td coordination.
Mentions: Photovoltaic effects in ferroelectrics (FE) have been studied for many decades123. Recently, the discovery of large photovoltages up to 15 V in multiferroic BiFeO3 films4 has drawn enormous attention to FE photovoltaics567. Different from traditional semiconductor solar cells, the photovoltaic effect in FE is relied on the polarization-induced internal electric field8910 (illustrated in Fig. 1a) instead of a p-n or Schottky junctions, which can not only improve the separation and migration of light-generated electron-hole pairs but also reduce the cost of cell fabrication. Moreover, the photo-induced voltages in multidomain ferroelectrics will not be limited to the Eg of light absorbers10 (see in Supplementary Fig. S1), superior to traditional semiconductor solar cells (<1 V). However, traditional FE are typically insulators of large band gaps (Eg) (supplementary Table S1) with rather limited light absorption and photocurrent, thus unsuitable for photovoltaic applications. Ideally, a photovoltaic material should have11 (1) a band gap of 1.0–1.8 eV matching the solar spectrum (Fig. 1b and 1c), (2) a large light absorption coefficient of ~104–105 cm−1 and (3) an intermediate carrier concentration of ~1015–1017 cm−3, in addition to being a polar material with a strong build-in electric field of ~104–105 V cm−1. Most FE fail to meet these requirements. For example, BiFeO3, which has attracted much recent attention412, features a relatively low solar cell efficiency (~ 3 × 10−3%) due to the relatively large band gap (2.6 eV)13 and the relatively high electrical resistance (~1010 Ω cm)14. Since light absorption and carrier concentrations are both band-gap dependent, small band gap polar materials are thus of great interest.

Bottom Line: Computational "materials genome" searches have predicted several exotic MO₆ FE with E(g) < 2.0 eV, all thus far unconfirmed because of synthesis difficulties.Here we report a new FE compound with MO₄ tetrahedral network, KBiFe₂O₅, which features narrow E(g) (1.6 eV), high Curie temperature (T(c) ~ 780 K) and robust magnetic and photoelectric activities.The high photovoltage (8.8 V) and photocurrent density (15 μA/cm²) were obtained, which is comparable to the reported BiFeO₃.

View Article: PubMed Central - PubMed

Affiliation: State Key Laboratory of Rare Earth Materials Chemistry and Applications, College of Chemistry and Molecular Engineering, Peking University, Beijing 100871, P.R. China.

ABSTRACT
Intrinsic polarization of ferroelectrics (FE) helps separate photon-generated charge carriers thus enhances photovoltaic effects. However, traditional FE with transition-metal cations (M) of d⁰ electron in MO₆ network typically has a band gap (E(g)) exceeding 3.0 eV. Although a smaller E(g) (2.6 eV) can be obtained in multiferroic BiFeO₃, the value is still too high for optimal solar energy applications. Computational "materials genome" searches have predicted several exotic MO₆ FE with E(g) < 2.0 eV, all thus far unconfirmed because of synthesis difficulties. Here we report a new FE compound with MO₄ tetrahedral network, KBiFe₂O₅, which features narrow E(g) (1.6 eV), high Curie temperature (T(c) ~ 780 K) and robust magnetic and photoelectric activities. The high photovoltage (8.8 V) and photocurrent density (15 μA/cm²) were obtained, which is comparable to the reported BiFeO₃. This finding may open a new avenue to discovering and designing optimal FE compounds for solar energy applications.

No MeSH data available.


Related in: MedlinePlus