Goddard_PhysRevMaterials.5.035403.pdf (3.7 MB)

Chlorine passivation of grain boundaries in cadmium telluride solar cells

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journal contribution
posted on 15.04.2021, 12:55 by Michael Watts, Peter Hatton, Roger Smith, Tom Fiducia, Ali Abbas, Rachael Greenhalgh, Michael Walls, Pooja Goddard
Cadmium Telluride is the most commercially important second generation thin film photovoltaic, with a record solar cell conversion efficiency of 22.1%. However as-deposited cells are <5% efficient and require a cell activation treatment with CdCl2 at about 400 ◦C to reach commercially viable efficiencies. Such a treatment is a routine process during CdTe module manufacturing. However, the precise mechanisms at work for this remarkable efficiency enhancement are not well understood. In this paper, atomistic modelling techniques are used to improve the fundamental understanding of the structural and electronic properties of CdTe by modelling the effects of chlorine and other elements with their interaction with extended defects and grain boundaries. Studies at high spatial resolution with NanoSIMS, TEM and Energy Dispersive X-ray analysis shows that chlorine atoms are concentrated at grain boundaries in CdTe after the CdCl2 treatment. DFT calculations show that both ClTe and for the first time Cli are stabilised at the grain boundaries compared to bulk CdTe. Similar defect formation energies of these defects suggests both will be present at the grain boundaries. As expected, four single particle levels are present in the Σ3 (112) GB band gap which explains the low efficiencies prior to treatment. ClTe substitutions passivate one of these levels and partially passivate another two. Remarkably further addition of Cli fully passivates the remaining single particle levels. This passivation of single particle levels is most likely to be the primary cause of the efficiency enhancement on chlorine treatment. Further to this, alternative halogens were then trialled as activation treatments. All halogens show similar electronic effects and their defect formation energies follow ionic radii trends.

Funding

Proposal for a Tier 2 Centre - HPC Midlands Plus

Engineering and Physical Sciences Research Council

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MATERIALS CHEMISTRY HIGH END COMPUTING CONSORTIUM

Engineering and Physical Sciences Research Council

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HIGH END COMPUTING MATERIALS CHEMISTRY CONSORTIUM

Engineering and Physical Sciences Research Council

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Tier 2 Hub in Materials and Molecular Modelling

Engineering and Physical Sciences Research Council

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History

School

  • Science
  • Mechanical, Electrical and Manufacturing Engineering

Department

  • Chemistry
  • Mathematical Sciences

Research Unit

  • Centre for Renewable Energy Systems Technology (CREST)

Published in

Physical Review Materials

Volume

5

Issue

3

Publisher

American Physical Society

Version

VoR (Version of Record)

Rights holder

© American Physical Society

Publisher statement

This paper was accepted for publication in the journal Physical Review Materials and the definitive published version is available at https://doi.org/10.1103/PhysRevMaterials.5.035403

Acceptance date

04/02/2021

Publication date

2021-03-03

Copyright date

2021

ISSN

2475-9953

Language

en

Depositor

Dr Pooja Goddard. Deposit date: 12 April 2021

Article number

035403

Exports

Loughborough Publications

Categories

Exports