Lone-pair effect on carrier capture in Cu                         2                         ZnSnS                         4                          solar cells

Sunghyun Kim; Ji Sang Park; Samantha N. Hood; Aron Walsh

doi:10.1039/c8ta10130b

Lone-pair effect on carrier capture in Cu ₂ ZnSnS ₄ solar cells

Sunghyun Kim, Ji Sang Park, Samantha N. Hood, Aron Walsh

Department of Materials Science and Engineering

Research output: Contribution to journal › Article › peer-review

41 Citations (Scopus)

Abstract

The performance of kesterite thin-film solar cells is limited by a low open-circuit voltage due to defect-mediated electron-hole recombination. We calculate the non-radiative carrier-capture cross sections and Shockley-Read-Hall recombination coefficients of deep-level point defects in Cu ₂ ZnSnS ₄ (CZTS) from first-principles. While the oxidation state of Sn is +4 in stoichiometric CZTS, inert lone pair (5s ² ) formation lowers the oxidation state to +2. The stability of the lone pair suppresses the ionization of certain point defects, inducing charge transition levels deep in the band gap. We find large lattice distortions associated with the lone-pair defect centers due to the difference in ionic radii between Sn(ii) and Sn(iv). The combination of a deep trap level and large lattice distortion facilitates efficient non-radiative carrier capture, with capture cross-sections exceeding 10 ^-12 cm ² . The results highlight a connection between redox active cations and 'killer' defect centres that form giant carrier traps. This lone pair effect will be relevant to other emerging photovoltaic materials containing ns ² cations.

Original language	English
Pages (from-to)	2686-2693
Number of pages	8
Journal	Journal of Materials Chemistry A
Volume	7
Issue number	6
DOIs	https://doi.org/10.1039/c8ta10130b
Publication status	Published - 2019

Bibliographical note

Funding Information:
We acknowledge support from the Royal Society, the EPSRC (Grant No. EP/K016288/1), and the EU Horizon2020 Framework (STARCELL, Grant No. 720907). We are grateful to the UK Materials and Molecular Modeling Hub for computational resources, which is partially funded by EPSRC (EP/P020194/1). Via our membership of the UK's HEC Materials Chemistry Consortium, which is funded by EPSRC (EP/L000202), this work used the ARCHER UK National Supercomputing Service (http:// www.archer.ac.uk). This work was also supported by a National Research Foundation of Korea (NRF) grant funded by the Korean government (MSIT) (No. 2018R1C1B6008728).

Publisher Copyright:
© 2019 The Royal Society of Chemistry.

All Science Journal Classification (ASJC) codes

Chemistry(all)
Renewable Energy, Sustainability and the Environment
Materials Science(all)

UN SDGs

This output contributes to the following UN Sustainable Development Goals (SDGs)

Access to Document

10.1039/c8ta10130b

Cite this

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title = " Lone-pair effect on carrier capture in Cu 2 ZnSnS 4 solar cells ",

abstract = " The performance of kesterite thin-film solar cells is limited by a low open-circuit voltage due to defect-mediated electron-hole recombination. We calculate the non-radiative carrier-capture cross sections and Shockley-Read-Hall recombination coefficients of deep-level point defects in Cu 2 ZnSnS 4 (CZTS) from first-principles. While the oxidation state of Sn is +4 in stoichiometric CZTS, inert lone pair (5s 2 ) formation lowers the oxidation state to +2. The stability of the lone pair suppresses the ionization of certain point defects, inducing charge transition levels deep in the band gap. We find large lattice distortions associated with the lone-pair defect centers due to the difference in ionic radii between Sn(ii) and Sn(iv). The combination of a deep trap level and large lattice distortion facilitates efficient non-radiative carrier capture, with capture cross-sections exceeding 10 -12 cm 2 . The results highlight a connection between redox active cations and 'killer' defect centres that form giant carrier traps. This lone pair effect will be relevant to other emerging photovoltaic materials containing ns 2 cations.",

author = "Sunghyun Kim and Park, {Ji Sang} and Hood, {Samantha N.} and Aron Walsh",

note = "Funding Information: We acknowledge support from the Royal Society, the EPSRC (Grant No. EP/K016288/1), and the EU Horizon2020 Framework (STARCELL, Grant No. 720907). We are grateful to the UK Materials and Molecular Modeling Hub for computational resources, which is partially funded by EPSRC (EP/P020194/1). Via our membership of the UK's HEC Materials Chemistry Consortium, which is funded by EPSRC (EP/L000202), this work used the ARCHER UK National Supercomputing Service (http:// www.archer.ac.uk). This work was also supported by a National Research Foundation of Korea (NRF) grant funded by the Korean government (MSIT) (No. 2018R1C1B6008728). Publisher Copyright: {\textcopyright} 2019 The Royal Society of Chemistry.",

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Lone-pair effect on carrier capture in Cu ₂ ZnSnS ₄ solar cells . / Kim, Sunghyun; Park, Ji Sang; Hood, Samantha N. et al.

In: Journal of Materials Chemistry A, Vol. 7, No. 6, 2019, p. 2686-2693.

Research output: Contribution to journal › Article › peer-review

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AU - Walsh, Aron

N1 - Funding Information: We acknowledge support from the Royal Society, the EPSRC (Grant No. EP/K016288/1), and the EU Horizon2020 Framework (STARCELL, Grant No. 720907). We are grateful to the UK Materials and Molecular Modeling Hub for computational resources, which is partially funded by EPSRC (EP/P020194/1). Via our membership of the UK's HEC Materials Chemistry Consortium, which is funded by EPSRC (EP/L000202), this work used the ARCHER UK National Supercomputing Service (http:// www.archer.ac.uk). This work was also supported by a National Research Foundation of Korea (NRF) grant funded by the Korean government (MSIT) (No. 2018R1C1B6008728). Publisher Copyright: © 2019 The Royal Society of Chemistry.

PY - 2019

Y1 - 2019

N2 - The performance of kesterite thin-film solar cells is limited by a low open-circuit voltage due to defect-mediated electron-hole recombination. We calculate the non-radiative carrier-capture cross sections and Shockley-Read-Hall recombination coefficients of deep-level point defects in Cu 2 ZnSnS 4 (CZTS) from first-principles. While the oxidation state of Sn is +4 in stoichiometric CZTS, inert lone pair (5s 2 ) formation lowers the oxidation state to +2. The stability of the lone pair suppresses the ionization of certain point defects, inducing charge transition levels deep in the band gap. We find large lattice distortions associated with the lone-pair defect centers due to the difference in ionic radii between Sn(ii) and Sn(iv). The combination of a deep trap level and large lattice distortion facilitates efficient non-radiative carrier capture, with capture cross-sections exceeding 10 -12 cm 2 . The results highlight a connection between redox active cations and 'killer' defect centres that form giant carrier traps. This lone pair effect will be relevant to other emerging photovoltaic materials containing ns 2 cations.

AB - The performance of kesterite thin-film solar cells is limited by a low open-circuit voltage due to defect-mediated electron-hole recombination. We calculate the non-radiative carrier-capture cross sections and Shockley-Read-Hall recombination coefficients of deep-level point defects in Cu 2 ZnSnS 4 (CZTS) from first-principles. While the oxidation state of Sn is +4 in stoichiometric CZTS, inert lone pair (5s 2 ) formation lowers the oxidation state to +2. The stability of the lone pair suppresses the ionization of certain point defects, inducing charge transition levels deep in the band gap. We find large lattice distortions associated with the lone-pair defect centers due to the difference in ionic radii between Sn(ii) and Sn(iv). The combination of a deep trap level and large lattice distortion facilitates efficient non-radiative carrier capture, with capture cross-sections exceeding 10 -12 cm 2 . The results highlight a connection between redox active cations and 'killer' defect centres that form giant carrier traps. This lone pair effect will be relevant to other emerging photovoltaic materials containing ns 2 cations.

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