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New insights on the nature of impurity levels in V-doped In2S3: why is it impossible to obtain a metallic intermediate band?

Ghorbani, Elaheh and Erhart, Paul and Albe, Karsten (2019):
New insights on the nature of impurity levels in V-doped In2S3: why is it impossible to obtain a metallic intermediate band?
In: Journal of Materials Chemistry A, RSC Publishing, pp. 7745-7751, 7, (13), ISSN 2050-7488,
DOI: 10.1039/C9TA01629E,
[Online-Edition: http://dx.doi.org/10.1039/C9TA01629E],
[Article]

Abstract

Generation of metallic intermediate band (IB) in a semiconductor material is a key challenge for increasing the efficiency of solar cells. The formation of a partially filled IB inside the band gap of V-doped In2S3 (In2S3:V) was first predicted by first principles calculations, based on density functional theory (DFT) [Palacios et al., Phys. Rev. Lett.101, 046403 (2008)]. It is well established, however, that DFT severely underestimates the band gap and overestimates the exchange coupling constant of semiconductors and insulators. As a consequence, predictions of impurity-induced gap levels and their splitting can be flawed. In this work, we revisit In2S3:V, using a band gap corrected method (hybrid functional) and explain that the optimistic but erroneous DFT-predicted partially filled IB was caused by neglecting the strongly correlated nature of d-electrons and the present Jahn–Teller effect. Furthermore, recalling the fact that transition metals embedded in semiconductors tend to change their oxidation state, we analyze rehybridization of V d-orbitals with S p-orbitals for different oxidation states of the incorporated V. Our results demonstrate that in the presence of a reducing agent (for instance, H+), a totally filled IB can appear in In2S3:V. Successful operation of the IB solar cell is, however, strongly correlated to the metallic character of the formed IB, simply due to its ability in both receiving and promoting electrons through absorption of lower energy photons. Though, since this filled IB is non-metallic, these levels can act as active recombination centers and deteriorate the efficiency of device, which is opposite the primary goal of obtaining them.

Item Type: Article
Erschienen: 2019
Creators: Ghorbani, Elaheh and Erhart, Paul and Albe, Karsten
Title: New insights on the nature of impurity levels in V-doped In2S3: why is it impossible to obtain a metallic intermediate band?
Language: English
Abstract:

Generation of metallic intermediate band (IB) in a semiconductor material is a key challenge for increasing the efficiency of solar cells. The formation of a partially filled IB inside the band gap of V-doped In2S3 (In2S3:V) was first predicted by first principles calculations, based on density functional theory (DFT) [Palacios et al., Phys. Rev. Lett.101, 046403 (2008)]. It is well established, however, that DFT severely underestimates the band gap and overestimates the exchange coupling constant of semiconductors and insulators. As a consequence, predictions of impurity-induced gap levels and their splitting can be flawed. In this work, we revisit In2S3:V, using a band gap corrected method (hybrid functional) and explain that the optimistic but erroneous DFT-predicted partially filled IB was caused by neglecting the strongly correlated nature of d-electrons and the present Jahn–Teller effect. Furthermore, recalling the fact that transition metals embedded in semiconductors tend to change their oxidation state, we analyze rehybridization of V d-orbitals with S p-orbitals for different oxidation states of the incorporated V. Our results demonstrate that in the presence of a reducing agent (for instance, H+), a totally filled IB can appear in In2S3:V. Successful operation of the IB solar cell is, however, strongly correlated to the metallic character of the formed IB, simply due to its ability in both receiving and promoting electrons through absorption of lower energy photons. Though, since this filled IB is non-metallic, these levels can act as active recombination centers and deteriorate the efficiency of device, which is opposite the primary goal of obtaining them.

Journal or Publication Title: Journal of Materials Chemistry A
Volume: 7
Number: 13
Publisher: RSC Publishing
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 Modelling
Zentrale Einrichtungen
Zentrale Einrichtungen > University IT-Service and Computing Centre (HRZ)
Zentrale Einrichtungen > University IT-Service and Computing Centre (HRZ) > Hochleistungsrechner
Date Deposited: 11 Apr 2019 11:39
DOI: 10.1039/C9TA01629E
Official URL: http://dx.doi.org/10.1039/C9TA01629E
Funders: German FederalMinistry for Economic Affairs and Energy (BMWi)
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