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Charge carrier dynamics and self-trapping on Sb2S3(100)


Grad, Lisa; von Rohr, Fabian O; Hengsberger, Matthias; Osterwalder, Jürg (2021). Charge carrier dynamics and self-trapping on Sb2S3(100). Physical Review Materials, 5(7):075401.

Abstract

Antimony sulfide (Sb2S3) is a promising material for solar energy conversion. It consists of earth-abundant elements with a low toxicity and high stability. Furthermore, it shows suitable optical and electronic properties like a large absorption coefficient and a convenient band gap of 1.7 eV. Nevertheless, so far, the obtained power conversion efficiencies and the open circuit voltages are far below the theoretical limits and need to be increased for a viable application of Sb2S3-based cells at the large scale. To achieve this it is important to identify the dominating loss mechanism. Here time-resolved two-photon photoemission experiments are presented from the (100) surface of a cleaved Sb2S3 single-crystal to investigate the charge carrier dynamics after photoexcitation. Based on these measurements an ultrafast relaxation within below 150 fs towards the conduction band minimum is observed. This is followed by a decay within 1 ps into states, which are located in the band gap 0.06 eV and 0.44 eV below the conduction band minimum where the charge carriers have long lifetimes of 27 ps and 63 ps, respectively. Based on the energetic position, the energy width and the formation time of the lower-lying gap state a self-trapping mechanism of free charge carriers by optical phonons with a frequency of 1.44 THz is proposed, and the results are discussed in this context. These findings provide evidence that the poor performance of Sb2S3 in solar devices can be traced back to intrinsically formed traps that can hardly be avoided.

Abstract

Antimony sulfide (Sb2S3) is a promising material for solar energy conversion. It consists of earth-abundant elements with a low toxicity and high stability. Furthermore, it shows suitable optical and electronic properties like a large absorption coefficient and a convenient band gap of 1.7 eV. Nevertheless, so far, the obtained power conversion efficiencies and the open circuit voltages are far below the theoretical limits and need to be increased for a viable application of Sb2S3-based cells at the large scale. To achieve this it is important to identify the dominating loss mechanism. Here time-resolved two-photon photoemission experiments are presented from the (100) surface of a cleaved Sb2S3 single-crystal to investigate the charge carrier dynamics after photoexcitation. Based on these measurements an ultrafast relaxation within below 150 fs towards the conduction band minimum is observed. This is followed by a decay within 1 ps into states, which are located in the band gap 0.06 eV and 0.44 eV below the conduction band minimum where the charge carriers have long lifetimes of 27 ps and 63 ps, respectively. Based on the energetic position, the energy width and the formation time of the lower-lying gap state a self-trapping mechanism of free charge carriers by optical phonons with a frequency of 1.44 THz is proposed, and the results are discussed in this context. These findings provide evidence that the poor performance of Sb2S3 in solar devices can be traced back to intrinsically formed traps that can hardly be avoided.

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Additional indexing

Item Type:Journal Article, refereed, original work
Communities & Collections:07 Faculty of Science > Department of Chemistry
07 Faculty of Science > Physics Institute
08 Research Priority Programs > Solar Light to Chemical Energy Conversion
Dewey Decimal Classification:540 Chemistry
Scopus Subject Areas:Physical Sciences > General Materials Science
Physical Sciences > Physics and Astronomy (miscellaneous)
Uncontrolled Keywords:Physics and Astronomy (miscellaneous), General Materials Science
Language:English
Date:8 July 2021
Deposited On:09 Feb 2022 08:05
Last Modified:26 Feb 2024 02:47
Publisher:American Physical Society
ISSN:2475-9953
OA Status:Hybrid
Publisher DOI:https://doi.org/10.1103/physrevmaterials.5.075401
Project Information:
  • : FunderSNSF
  • : Grant ID200020_172641
  • : Project TitleSurface physics with single-layer materials and molecular layers
  • Content: Published Version