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Charge Transport and Defects in Sulfur-Deficient Chalcogenide Perovskite $Ba Zr S$ $_{3}$

Garima Aggarwal ^1,*,†, Adeem Saeed Mirza^2,‡, Stefania Riva ^3,‡, Corrado Comparotto ¹, Robert J. W. Frost ⁴, Soham Mukherjee ³, Monica Morales-Masis ², Håkan Rensmo³, and Jonathan Staaf Scragg ¹

¹Division of Solar Cell Technology, Department of Materials Science and Engineering, Uppsala University, 75237 Uppsala, Sweden
²MESA+ Institute for Nanotechnology, University of Twente, 7500 AE Enschede, The Netherlands
³Division of X-Ray Photon Science, Department of Physics and Astronomy, Uppsala University, Box 516, SE-75120 Uppsala, Sweden
⁴Division of Applied Nuclear Physics, Department of Physics and Astronomy, Uppsala University, Box 516, 75120 Uppsala, Sweden

^*Contact author: garima.agrawalsk@gmail.com
^†Now at Waaree Energies Limited, Mumbai, India
^‡These authors contributed equally to this work.

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PRX Energy 4, 033001 – Published 10 July, 2025

DOI: https://doi.org/10.1103/t7ns-99dk

Abstract

Exploring the conduction mechanism in the chalcogenide perovskite $Ba Zr S$ $_{3}$ is of significant interest due to its potential suitability as a top absorber layer in silicon-based tandem solar cells and other optoelectronic applications. Theoretical and experimental studies anticipate native ambipolar doping in $Ba Zr S$ $_{3}$ , although experimental validation remains limited. This study reveals a transition from highly insulating behavior to $n$ -type conductivity (approximately $100$ S/cm) in $Ba Zr S$ $_{3}$ thin films through annealing in an $S$ -poor environment. $Ba Zr S$ $_{3}$ thin films are synthesized via a two-step process: co-sputtering of $Ba$ - $Zr$ followed by sulfurization at $600^{\circ} C$ , and subsequent annealing in high vacuum. Ultraviolet-visible spectroscopy measurements reveal a red shift of approximately $100$ meV in the band gap concurrent with sample-color darkening after vacuum annealing. The increase in defect density from the order of $10^{17}$ to $10^{21} {cm}^{- 3}$ with vacuum annealing, coupled with the low activation energy (approximately $8$ meV), and the $n$ -type character of the defects, strongly suggests that sulfur vacancies ( $V_{S}$ ) are responsible for the $n$ -type doping, in agreement with theoretical predictions. Temperature-dependent Hall measurement shows that phonon scattering governs charge transport at room temperature in $Ba Zr S$ $_{3}$ films and that $S$ vacancies are shallow donor defects acting as a weak impurity metal. The shift of the valence-band maximum (VBM) with respect to the Fermi level, quantified by hard x-ray photoelectron spectroscopy ( $Ga$ $K α$ , 9.25 keV), further corroborates the induced $n$ type of conductivity in annealed samples. Our findings indicate that vacuum annealing induces $V_{S}$ defects that dominate charge transport, resulting in $n$ -type conductivity in $Ba Zr S$ $_{3}$ under $S$ -poor conditions. These discoveries will inform important design choices, such as selecting appropriate contact materials, for integrating $Ba Zr S$ $_{3}$ into solar cell structures or other devices.

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Chalcogenide perovskites such as $Ba Zr S$ $_{3}$ are promising materials for solar cells and optoelectronic devices due to their earth-abundant composition and excellent optical properties. However, controlling their electrical conductivity remains a challenge. This study demonstrates that annealing $Ba Zr S$ $_{3}$ thin films in a sulfur-deficient environment introduces sulfur vacancies, transforming the material from highly insulating to n-type conductive. Using optical absorption, Hall measurements, and X-ray spectroscopy, the authors reveal that these vacancies act as shallow donors, boosting the conductivity up to 100 S/cm. These findings provide a pathway to tailor the electrical properties of $Ba Zr S$ $_{3}$ by adjusting the annealing conditions, offering insight for future device integration. These results will aid in optimizing $Ba Zr S$ $_{3}$ for applications in tandem solar cells, light-emitting diodes, and other optoelectronic technologies.

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References (52)

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PRX Energy 4, 033001– Published 10 July, 2025

Vol. 4, Iss. 3 — July - September 2025

Received 15 February 2025
Revised 19 May 2025
Accepted 17 June 2025

DOI: https://doi.org/10.1103/t7ns-99dk

Published by the American Physical Society under the terms of the Creative Commons Attribution 4.0 International license. Further distribution of this work must maintain attribution to the author(s) and the published article's title, journal citation, and DOI.

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Charge Transport and Defects in Sulfur-Deficient Chalcogenide Perovskite $Ba Zr S$ $_{3}$

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Charge Transport and Defects in Sulfur-Deficient Chalcogenide Perovskite BaZrS3

Abstract

Physics Subject Headings (PhySH)

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Article Text

Supplemental Material

References (52)

Charge Transport and Defects in Sulfur-Deficient Chalcogenide Perovskite $Ba Zr S$ $_{3}$