Bandgap-Adjustment and Enhanced Surface Photovoltage in Y-Substituted LaTaIVO2N

Bibliographic Details
Title:	Bandgap-Adjustment and Enhanced Surface Photovoltage in Y-Substituted LaTaIVO2N
Authors:	Bubeck, Cora, Widenmeyer, Marc, Denko, Alexandra T. de, Richter, Gunther, Coduri, Mauro, Colera, Eduardo Salas, Goering, Eberhard, Zhang, Hongbin, Yoon, Songhak, Osterloh, Frank E., Weidenkaff, Anke
Publication Year:	2020
Collection:	Publikationsdatenbank der Fraunhofer-Gesellschaft
Subject Terms:	absorption structure, carrier generation, charge carrier recombination, charge carrier, crystal structure, crystal structure analysis, density functional theory, energy gap, films, lanthanum compounds, microcrystals, N-type semiconductors, perovskite, Photons, surface photovoltage spectroscopy, surface property, tantalum compounds, transparent conductor, weight fractions, X-ray photoelectron spectroscopy
Time:	541
Description:	S.11837-11848 ; 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 unsusal red/orange color of the Ta4+-containing perovskites. In combination with crystal structure analysis the DFT calculations identified the orthorhombic strain as main descriptor for the unexpected trend of the optical bandgap (EG,x=0.3 ≈ EG,x=0EG,x=0.1EG,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 material. 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. ; 8 ; Nr.23
Document Type:	article in journal/newspaper
Language:	English
Relation:	Journal of materials chemistry. A, Materials for energy and sustainability; https://publica.fraunhofer.de/handle/publica/262840
DOI:	10.1039/D0TA02136A
Availability:	https://doi.org/10.1039/D0TA02136A https://publica.fraunhofer.de/handle/publica/262840
Accession Number:	edsbas.644258E8
Database:	BASE

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