TU Darmstadt / ULB / TUbiblio

Bandgap-adjustment and enhanced surface photovoltage in Y-substituted LaTaIVO2N

Bubeck, Cora and Widenmeyer, Marc and De Denko, Alexandra T. and Richter, Gunther and Coduri, Mauro and Colera, Eduardo Salas and Goering, Eberhard and Zhang, Hongbin and Yoon, Songhak and Osterloh, Frank E. and Weidenkaff, Anke (2020):
Bandgap-adjustment and enhanced surface photovoltage in Y-substituted LaTaIVO2N.
8, In: Journal of Materials Chemistry A, (23), pp. 11837-11848. ISSN 2050-7488,
DOI: 10.1039/D0TA02136A,
[Article]

Abstract

Perovskite-type oxynitrides AB(O,N)3 are photocatalysts for overall water splitting under visible light illumination. In the past, structurally labile perovskite-type oxynitrides (e.g. YTaON2) were predicted to be highly suitable. In this work, we tackle the challenging YTa(O,N)3 synthesis by Y-substitution in LaTaIVO2N resulting in phase-pure La0.9Y0.1TaIVO2N, La0.75Y0.25TaIVO2N, and La0.7Y0.3TaIVO2N. By using microcrystalline YTaO4 together with an unconventional ammonolysis protocol we synthesized the highest reported weight fraction (82(2) wt%) of perovskite-type YTa(O,N)3. Ta4+ in La1−xYxTaIVO2N was verified by X-ray photoelectron spectroscopy (XPS) and X-ray near edge absorption structure (XANES) analysis. Density functional theory (DFT) calculations revealed a transparent conductor-like behavior explaining the unusual red/orange color of the Ta4+-containing perovskites. In combination with crystal structure analysis the DFT calculations identified orthorhombic strain as the main descriptor for the unexpected trend of the optical bandgap (EG,x=0.3 ≈ EG,x=0 < EG,x=0.1 < EG,x=0.25). Surface photovoltage spectroscopy (SPS) of particulate La1−xYxTaIVO2N (x = 0, 0.1, 0.25, 0.3) films revealed negative photovoltages at photon energies exceeding 1.75 eV, confirming that these materials are n-type semiconductors with effective bandgaps of ∼1.75 eV irrespective of the Y content. The photovoltage values increased with the Y content, suggesting an improved carrier generation and separation in the materials. However, increasing the Y content also slowed down the timescales for photovoltage generation/decay indicating trap states in the materials. Based on our results, we suggest a significantly weaker as classically assumed impact of reduced B-site metal cations such as Ta4+ on the photovoltage and charge carrier recombination rate.

Item Type: Article
Erschienen: 2020
Creators: Bubeck, Cora and Widenmeyer, Marc and De Denko, Alexandra T. and Richter, Gunther and Coduri, Mauro and Colera, Eduardo Salas and Goering, Eberhard and Zhang, Hongbin and Yoon, Songhak and Osterloh, Frank E. and Weidenkaff, Anke
Title: Bandgap-adjustment and enhanced surface photovoltage in Y-substituted LaTaIVO2N
Language: English
Abstract:

Perovskite-type oxynitrides AB(O,N)3 are photocatalysts for overall water splitting under visible light illumination. In the past, structurally labile perovskite-type oxynitrides (e.g. YTaON2) were predicted to be highly suitable. In this work, we tackle the challenging YTa(O,N)3 synthesis by Y-substitution in LaTaIVO2N resulting in phase-pure La0.9Y0.1TaIVO2N, La0.75Y0.25TaIVO2N, and La0.7Y0.3TaIVO2N. By using microcrystalline YTaO4 together with an unconventional ammonolysis protocol we synthesized the highest reported weight fraction (82(2) wt%) of perovskite-type YTa(O,N)3. Ta4+ in La1−xYxTaIVO2N was verified by X-ray photoelectron spectroscopy (XPS) and X-ray near edge absorption structure (XANES) analysis. Density functional theory (DFT) calculations revealed a transparent conductor-like behavior explaining the unusual red/orange color of the Ta4+-containing perovskites. In combination with crystal structure analysis the DFT calculations identified orthorhombic strain as the main descriptor for the unexpected trend of the optical bandgap (EG,x=0.3 ≈ EG,x=0 < EG,x=0.1 < EG,x=0.25). Surface photovoltage spectroscopy (SPS) of particulate La1−xYxTaIVO2N (x = 0, 0.1, 0.25, 0.3) films revealed negative photovoltages at photon energies exceeding 1.75 eV, confirming that these materials are n-type semiconductors with effective bandgaps of ∼1.75 eV irrespective of the Y content. The photovoltage values increased with the Y content, suggesting an improved carrier generation and separation in the materials. However, increasing the Y content also slowed down the timescales for photovoltage generation/decay indicating trap states in the materials. Based on our results, we suggest a significantly weaker as classically assumed impact of reduced B-site metal cations such as Ta4+ on the photovoltage and charge carrier recombination rate.

Journal or Publication Title: Journal of Materials Chemistry A
Volume: 8
Number: 23
Divisions: 11 Department of Materials and Earth Sciences
11 Department of Materials and Earth Sciences > Material Science
11 Department of Materials and Earth Sciences > Material Science > Materials and Resources
Date Deposited: 17 Jun 2020 07:18
DOI: 10.1039/D0TA02136A
Official URL: https://doi.org/10.1039/D0TA02136A
Projects: The authors acknowledge the financial support and granted radiation beam time of the European Synchrotron Radiation Facility, Grenoble, France and Heinz Maier-Leibnitz Zentrum (MLZ), Garching, Germany., This work was supported by the Deutsche Forschungsgemeinschaft within the priority program SPP 1613 “Solar H2” (WE 2803/7-1)., Support for surface photovoltage spectroscopy measurements was provided by the U.S. Department of Energy, Office of Science, Office of Basic Energy Sciences, under Grant DOE-SC0015329.
Export:
Suche nach Titel in: TUfind oder in Google
Send an inquiry Send an inquiry

Options (only for editors)
Show editorial Details Show editorial Details