Abundance of CuZn+ SnZn and 2CuZn +Sn Zn defect clusters in kesterite solar cells

Shiyou Chen; Lin Wang Wang; Aron Walsh; X. G. Gong; Su Huai Wei

doi:10.1063/1.4768215

Abundance of Cu_Zn+ Sn_Zn and 2Cu_Zn +Sn _Zn defect clusters in kesterite solar cells

Shiyou Chen, Lin Wang Wang, Aron Walsh, X. G. Gong, Su Huai Wei

Department of Physics

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

145 Scopus citations

Abstract

Kesterite solar cells show the highest efficiency when the absorber layers (Cu₂ ZnSnS₄ [CZTS], Cu₂ ZnSnSe₄ [CZTSe] and their alloys) are non-stoichiometric with Cu / (Zn + Sn) ≈ 0.8 and Zn / Sn ≈ 1.2. The fundamental cause is so far not understood. Using a first-principles theory, we show that passivated defect clusters such as Cu _Zn+ Sn_Zn and 2 Cu_Zn+ Sn_Zn have high concentrations even in stoichiometric samples with Cu/(ZnSn) and Zn/Sn ratios near 1. The partially passivated Cu_Zn+ Sn_Zn cluster produces a deep donor level in the band gap of CZTS, and the fully passivated 2Cu_Zn+ Sn_Zn cluster causes a significant band gap decrease. Both effects are detrimental to photovoltaic performance, so Zn-rich and Cu, Sn-poor conditions are required to prevent their formation and increase the efficiency. The donor level is relatively shallower in CZTSe than in CZTS, which gives an explanation to the higher efficiency obtained in Cu₂ ZnSn (S, Se)₄ (CZTSSe) cells with high Se content.

Original language	English
Article number	223901
Journal	Applied Physics Letters
Volume	101
Issue number	22
DOIs	https://doi.org/10.1063/1.4768215
State	Published - 26 Nov 2012

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Cite this

@article{94916259dd6a43759cf044e1fd1b568f,

title = "Abundance of CuZn+ SnZn and 2CuZn +Sn Zn defect clusters in kesterite solar cells",

abstract = "Kesterite solar cells show the highest efficiency when the absorber layers (Cu2 ZnSnS4 [CZTS], Cu2 ZnSnSe4 [CZTSe] and their alloys) are non-stoichiometric with Cu / (Zn + Sn) ≈ 0.8 and Zn / Sn ≈ 1.2. The fundamental cause is so far not understood. Using a first-principles theory, we show that passivated defect clusters such as Cu Zn+ SnZn and 2 CuZn+ SnZn have high concentrations even in stoichiometric samples with Cu/(ZnSn) and Zn/Sn ratios near 1. The partially passivated CuZn+ SnZn cluster produces a deep donor level in the band gap of CZTS, and the fully passivated 2CuZn+ SnZn cluster causes a significant band gap decrease. Both effects are detrimental to photovoltaic performance, so Zn-rich and Cu, Sn-poor conditions are required to prevent their formation and increase the efficiency. The donor level is relatively shallower in CZTSe than in CZTS, which gives an explanation to the higher efficiency obtained in Cu2 ZnSn (S, Se)4 (CZTSSe) cells with high Se content.",

author = "Shiyou Chen and Wang, {Lin Wang} and Aron Walsh and Gong, {X. G.} and Wei, {Su Huai}",

note = "Funding Information: The work in China was supported by NSF of China (Nos. 61106087 and 10934002), the Special Funds for Major State Basic Research (No. 2012CB921401), the Research Program of Shanghai municipality and MOE, PCSIRT and CC of ECNU. The work (manuscript preparation) performed in JCAP, a DOE Energy Innovation Hub, was supported through the Office of Science of the U.S. DOE under Award No. DE-SC0004993. A.W. acknowledges support from the Royal Society for a University Research Fellowship and EPSRC Grant No. EP/I01330X/1. The work at NREL was funded by the U.S. DOE, under Contract No. DE-AC36-08GO28308.",

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T1 - Abundance of CuZn+ SnZn and 2CuZn +Sn Zn defect clusters in kesterite solar cells

AU - Chen, Shiyou

AU - Wang, Lin Wang

AU - Walsh, Aron

AU - Gong, X. G.

AU - Wei, Su Huai

N1 - Funding Information: The work in China was supported by NSF of China (Nos. 61106087 and 10934002), the Special Funds for Major State Basic Research (No. 2012CB921401), the Research Program of Shanghai municipality and MOE, PCSIRT and CC of ECNU. The work (manuscript preparation) performed in JCAP, a DOE Energy Innovation Hub, was supported through the Office of Science of the U.S. DOE under Award No. DE-SC0004993. A.W. acknowledges support from the Royal Society for a University Research Fellowship and EPSRC Grant No. EP/I01330X/1. The work at NREL was funded by the U.S. DOE, under Contract No. DE-AC36-08GO28308.

PY - 2012/11/26

Y1 - 2012/11/26

N2 - Kesterite solar cells show the highest efficiency when the absorber layers (Cu2 ZnSnS4 [CZTS], Cu2 ZnSnSe4 [CZTSe] and their alloys) are non-stoichiometric with Cu / (Zn + Sn) ≈ 0.8 and Zn / Sn ≈ 1.2. The fundamental cause is so far not understood. Using a first-principles theory, we show that passivated defect clusters such as Cu Zn+ SnZn and 2 CuZn+ SnZn have high concentrations even in stoichiometric samples with Cu/(ZnSn) and Zn/Sn ratios near 1. The partially passivated CuZn+ SnZn cluster produces a deep donor level in the band gap of CZTS, and the fully passivated 2CuZn+ SnZn cluster causes a significant band gap decrease. Both effects are detrimental to photovoltaic performance, so Zn-rich and Cu, Sn-poor conditions are required to prevent their formation and increase the efficiency. The donor level is relatively shallower in CZTSe than in CZTS, which gives an explanation to the higher efficiency obtained in Cu2 ZnSn (S, Se)4 (CZTSSe) cells with high Se content.

AB - Kesterite solar cells show the highest efficiency when the absorber layers (Cu2 ZnSnS4 [CZTS], Cu2 ZnSnSe4 [CZTSe] and their alloys) are non-stoichiometric with Cu / (Zn + Sn) ≈ 0.8 and Zn / Sn ≈ 1.2. The fundamental cause is so far not understood. Using a first-principles theory, we show that passivated defect clusters such as Cu Zn+ SnZn and 2 CuZn+ SnZn have high concentrations even in stoichiometric samples with Cu/(ZnSn) and Zn/Sn ratios near 1. The partially passivated CuZn+ SnZn cluster produces a deep donor level in the band gap of CZTS, and the fully passivated 2CuZn+ SnZn cluster causes a significant band gap decrease. Both effects are detrimental to photovoltaic performance, so Zn-rich and Cu, Sn-poor conditions are required to prevent their formation and increase the efficiency. The donor level is relatively shallower in CZTSe than in CZTS, which gives an explanation to the higher efficiency obtained in Cu2 ZnSn (S, Se)4 (CZTSSe) cells with high Se content.

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