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Hatton P, Watts M, Zhou Y, Smith R, Goddard P. Arsenic doping and diffusion in CdTe: a DFT study of bulk and grain boundaries. JOURNAL OF PHYSICS. CONDENSED MATTER : AN INSTITUTE OF PHYSICS JOURNAL 2022; 35:075702. [PMID: 36541549 DOI: 10.1088/1361-648x/aca8e5] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Received: 10/07/2022] [Accepted: 12/05/2022] [Indexed: 06/17/2023]
Abstract
The doping of CdTe with As is a method which is thought to increase cell efficiency by increasing electron hole concentrations. This doping relies on the diffusion of As through CdTe resulting in AsTesubstitution. The potential effectiveness of this is considered through kinetic and electronic properties calculations in both bulk and Σ3 and Σ9 grain boundaries using Density Functional Theory. In bulk zinc-blende CdTe, isolated As diffuses with barriers <0.5 eV and with similar barriers through wurtzite structured CdTe, generated by stacking faults, suggesting that As will not be trapped at the stacking faults and hence the transport of isolated As will be unhindered in bulk CdTe. Substitutional arsenic in bulk CdTe has little effect on the band gap except when it is positively charged in the AX-centre position or occurring as a di-interstitial. However in contrast to the case of chlorine, arsenic present in the grain boundaries introduces defect states into the band gap. This suggests that a doping strategy whereby the grain boundaries are first saturated with chlorine, before single arsenic atoms are introduced, might be more beneficial.
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Affiliation(s)
- Peter Hatton
- Department of Mathematical Sciences, Loughborough University, Loughborough, Leicestershire LE11 3TU, United Kingdom
| | - Michael Watts
- Department of Chemistry, Loughborough University, Loughborough, Leicestershire LE11 3TU, United Kingdom
| | - Ying Zhou
- Department of Mathematical Sciences, Loughborough University, Loughborough, Leicestershire LE11 3TU, United Kingdom
| | - Roger Smith
- Department of Mathematical Sciences, Loughborough University, Loughborough, Leicestershire LE11 3TU, United Kingdom
| | - Pooja Goddard
- Department of Chemistry, Loughborough University, Loughborough, Leicestershire LE11 3TU, United Kingdom
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Hatton P, Watts MJ, Abbas A, Walls JM, Smith R, Goddard P. Chlorine activated stacking fault removal mechanism in thin film CdTe solar cells: the missing piece. Nat Commun 2021; 12:4938. [PMID: 34426582 PMCID: PMC8382740 DOI: 10.1038/s41467-021-25063-y] [Citation(s) in RCA: 6] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/16/2021] [Accepted: 07/12/2021] [Indexed: 11/15/2022] Open
Abstract
The conversion efficiency of as-deposited, CdTe solar cells is poor and typically less than 5%. A CdCl2 activation treatment increases this to up to 22%. Studies have shown that stacking faults (SFs) are removed and the grain boundaries (GBs) are decorated with chlorine. Thus, SF removal and device efficiency are strongly correlated but whether this is direct or indirect has not been established. Here we explain the passivation responsible for the increase in efficiency but also crucially elucidate the associated SF removal mechanism. The effect of chlorine on a model system containing a SF and two GBs is investigated using density functional theory. The proposed SF removal mechanisms are feasible at the 400 ∘C treatment temperature. It is concluded that the efficiency increase is due to electronic effects in the GBs while SF removal is a by-product of the saturation of the GB with chlorine but is a key signal that sufficient chlorine is present for passivation to occur.
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Affiliation(s)
- Peter Hatton
- Department of Mathematical Sciences, Loughborough University, Loughborough, Leicestershire, UK
| | - Michael J Watts
- Department of Chemistry, Loughborough University, Loughborough, Leicestershire, UK
| | - Ali Abbas
- Centre for Renewable Energy Systems Technology (CREST), Loughborough University, Loughborough, Leicestershire, UK
| | - John M Walls
- Centre for Renewable Energy Systems Technology (CREST), Loughborough University, Loughborough, Leicestershire, UK
| | - Roger Smith
- Department of Mathematical Sciences, Loughborough University, Loughborough, Leicestershire, UK
| | - Pooja Goddard
- Department of Chemistry, Loughborough University, Loughborough, Leicestershire, UK.
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Shah A, Nicholson AP, Fiducia TAM, Abbas A, Pandey R, Liu J, Grovenor C, Walls JM, Sampath WS, Munshi AH. Understanding the Copassivation Effect of Cl and Se for CdTe Grain Boundaries. ACS APPLIED MATERIALS & INTERFACES 2021; 13:35086-35096. [PMID: 34264063 DOI: 10.1021/acsami.1c06587] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/13/2023]
Abstract
Chlorine passivation treatment of cadmium telluride (CdTe) solar cells improves device performance by assisting electron-hole carrier separation at CdTe grain boundaries. Further improvement in device efficiency is observed after alloying the CdTe absorber layer with selenium. High-resolution secondary ion mass spectroscopy (NanoSIMS) imaging has been used to determine the distribution of selenium and chlorine at the CdTe grain boundaries in a selenium-graded CdTe device. Atomistic modeling based on density functional theory (DFT-1/2) further reveals that the presence of selenium and chlorine at an exemplar (110)/(100) CdTe grain boundary passivates critical acceptor defects and leads to n-type inversion at the grain boundary. The defect state analysis provides an explanation for the band-bending effects observed in the energy band alignment results, thereby elucidating mechanisms for high efficiencies observed in Se-alloyed and Cl-passivated CdTe solar cells.
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Affiliation(s)
- Akash Shah
- Department of Mechanical Engineering, Colorado State University, Fort Collins, Colorado 80523, United States
| | - Anthony P Nicholson
- Department of Mechanical Engineering, Colorado State University, Fort Collins, Colorado 80523, United States
| | - Thomas A M Fiducia
- CREST (Centre for Renewable Energy Systems Technology), Loughborough University, Loughborough, Leicestershire LE11 3TU, U.K
| | - Ali Abbas
- CREST (Centre for Renewable Energy Systems Technology), Loughborough University, Loughborough, Leicestershire LE11 3TU, U.K
| | - Ramesh Pandey
- Department of Physics, Colorado State University, Fort Collins, Colorado 80523, United States
| | - Junliang Liu
- Department of Materials, University of Oxford, Oxford OX1 2JD, U.K
| | - Chris Grovenor
- Department of Materials, University of Oxford, Oxford OX1 2JD, U.K
| | - John M Walls
- CREST (Centre for Renewable Energy Systems Technology), Loughborough University, Loughborough, Leicestershire LE11 3TU, U.K
| | - Walajabad S Sampath
- Department of Mechanical Engineering, Colorado State University, Fort Collins, Colorado 80523, United States
| | - Amit H Munshi
- Department of Mechanical Engineering, Colorado State University, Fort Collins, Colorado 80523, United States
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Liu D, Wang X, Zhang Y, Sa R. First-principles study of the stability, mechanical, electronic and optical properties of Cd0.75Hg0.25Se. Chem Phys 2021. [DOI: 10.1016/j.chemphys.2021.111164] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/22/2022]
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