Surface modification through air annealing Cu2ZnSn(S,Se)4 absorbers

Larsen, Jes K.; Ren, Yi; Ross, Nils; Särhammar, Erik; Li, S.-Y.; Platzer‐Björkman, Charlotte

doi:10.1016/j.tsf.2016.08.030

Cited by 33 publications

(30 citation statements)

References 19 publications

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“…Several papers have been published about the effect of post annealing of CZTSSe . However, due to the complexity of the starting material, especially the S/Se‐ratio and the various kind of impurities caused by the many different deposition methods used, and additionally due to the many kinds of post‐annealing chosen, such as different atmosphere type and pressure, different temperatures and performed at different stages of the solar cell fabrication, there is no general conclusion regarding a reason for the changes seen, and possibly, this might also differ from case to case.…”

Section: Resultsmentioning

confidence: 99%

Zinc‐Tin‐Oxide Buffer Layer and Low Temperature Post Annealing Resulting in a 9.0% Efficient Cd‐Free Cu₂ZnSnS₄ Solar Cell

Ericson¹,

Larsson²,

Törndahl³

et al. 2017

Solar RRL

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Zn 1-x Sn x O y (ZTO) has yielded promising results as buffer material for the full sulfur Cu 2 ZnSnS 4 (CZTS), with efficiencies continuously surpassing its CdS-references. ZTO can be deposited by atomic layer deposition (ALD) enabling tuning of the conduction band position through choice of metal ratio or deposition temperature. Thus an optimization of the conduction band alignment between ZTO and CZTS can be achieved. The ZTO bandgap is generally larger than that of CdS and can therefore yield higher currents due to reduced losses in the short wavelength region. Another advantage is the possibility to omit the toxic Cd. In this study the ALD process temperature was varied from 105 to 165 °C. Current-blocked devices were obtained at 105 °C while the highest open-circuit voltage and device efficiency was achieved for 145 °C. The highest fill factor was seen at 165 °C. The best efficiency reached in this study was 9.0 %, which, to our knowledge, is the highest efficiency reported for Cd-free full-sulfur CZTS. We also show that the effect of heat needs to be taken into 2 account. The results indicate that part of the device improvement comes from heating the absorber, but that the benefit of using a ZTO-buffer is clear.

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Section: Resultsmentioning

confidence: 99%

Zinc‐Tin‐Oxide Buffer Layer and Low Temperature Post Annealing Resulting in a 9.0% Efficient Cd‐Free Cu₂ZnSnS₄ Solar Cell

Ericson¹,

Larsson²,

Törndahl³

et al. 2017

Solar RRL

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“…The benefit of the air anneal was ascribed to the passivation of GB by SnO x and a reduced Cu content. In a comparison of air annealing treatments of bare CZTS and CZTSe absorbers, Zn-enrichment was seen after NH 4 OH etching in both cases, while removal of elemental selenium was only observed for CZTSe [146]. Higher annealing temperatures were beneficial for the selenide absorber and the efficiency improvements were also larger for CZTSe cells.…”

Section: Annealing Of the Heterojunctionmentioning

confidence: 94%

“…However, since this is a bulk effect, covered in other contributions of this special issue, it will not be discussed in depth here. Annealing of the absorber layer in air prior to buffer layer deposition has been shown to improve device performance by several groups [137,[145][146][147][148]. Sardashti et al [137] performed annealing in air at 300°C-400°C, followed by etching in NH 4 OH to achieve high performance devices (note that the performance of reference cells without air anneal was not given).…”

Section: Annealing Of the Heterojunctionmentioning

confidence: 99%

Back and front contacts in kesterite solar cells: state-of-the-art and open questions

et al. 2019

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We review the present state-of-the-art within back and front contacts in kesterite thin film solar cells, as well as the current challenges. At the back contact, molybdenum (Mo) is generally used, and thick Mo(S, Se) 2 films of up to several hundred nanometers are seen in record devices, in particular for selenium-rich kesterite. The electrical properties of Mo(S, Se) 2 can vary strongly depending on orientation and indiffusion of elements from the device stack, and there are indications that the back contact properties are less ideal in the sulfide as compared to the selenide case. However, the electronic interface structure of this contact is generally not well-studied and thus poorly understood, and more measurements are needed for a conclusive statement. Transparent back contacts is a relatively new topic attracting attention as crucial component in bifacial and multijunction solar cells. Front illuminated efficiencies of up to 6% have so far been achieved by adding interlayers that are not always fully transparent. For the front contact, a favorable energy level alignment at the kesterite/CdS interface can be confirmed for kesterite absorbers with an intermediate [S]/([S]+[Se]) composition. This agrees with the fact that kesterite absorbers of this composition reach highest efficiencies when CdS buffer layers are employed, while alternative buffer materials with larger band gap, such as Cd 1−x Zn x S or Zn 1−x Sn x O y , result in higher efficiencies than devices with CdS buffers when sulfurrich kesterite absorbers are used. Etching of the kesterite absorber surface, and annealing in air or inert atmosphere before or after buffer layer deposition, has shown strong impact on device performance. Heterojunction annealing to promote interdiffusion was used for the highest performing sulfide kesterite device and air-annealing was reported important for selenium-rich record solar cells. Cu 2 ZnSnS 4 (CZTS) absorbers for solar cell applications was first reported by Ito and Nakazawa [1]. Early results on CZTS device performance were reported by Friedlmeier et al [2], Seol et al [3], and Katagiri et al [4]. Later a group at IBM reached record performances with power conversion efficiencies (PCEs) above 10% for CZTSSe devices in 2010 [5] and the current record PCE of 12.6% in 2013 [6]. In 2018, researchers from DGIST reached the same performance, 12.6%, but for a larger device area [7]. The device structure used for kesterite solar cells was originally copied from that of Cu(In, Ga)Se 2 , (CIGSe) TFSCs, and is formed by sequential deposition, upon a soda lime glass substrate, of a Mo back contact, the absorber, a CdS buffer layer, and a ZnO/ZnO:Al bi-layer window (i.e. transparent top contact). This structure, schematically shown for CZTSSe in figure 1, is not necessarily ideal for kesterite solar cells, and extensive work has been invested into studies of alternative backand front contacts and related deposition processes. In this paper, the state-of-the-art and current open questions related to the back and front c...

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“…12 The selenizations were done in the same fashion as by Larsen et al 13 In order to achieve different anion ratios in the samples, the selenization temperature and duration were set for S1(S1 0 ), S2(S2 0 ), and S3(S3 0 ) in Table I as 530 C 10 min, 560 C 4 min, and 500 C, 10 min, respectively. The pure sulfide sample referred to as S4 in Table I was taken from our pervious work.…”

mentioning

confidence: 99%

Optical properties of Cu2ZnSn(SxSe1-x)4 solar absorbers: Spectroscopic ellipsometry and ab initio calculations

Zamulko

Persson

et al. 2017

Applied Physics Letters

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Dielectric functions of Cu2ZnSn(SxSe1-x)4 thin film absorbers with varied x were determined by spectroscopic ellipsometry and ab initio calculations. From the combination of experimental and theoretical studies, the fundamental interband transition energy E0 (∼1–1.5 eV) and the next following transition energy E1 (∼2–3 eV) were identified and found to blue-shift with increasing sulfur anion content, while keeping the energy separation E1−E0 almost constant, ∼1.4 eV from experiments, and 1 eV from theory. In addition, the average dielectric responses were found to decrease with sulfur anion content from both theoretical and experimental results. The Tauc optical bandgap value Eg determined on samples prepared on Mo and soda lime glass substrate showed a positive linear relationship between x and bandgap Eg. The bandgap bowing factor determined from the theoretical data is 0.09 eV.

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Surface modification through air annealing Cu2ZnSn(S,Se)4 absorbers

Cited by 33 publications

References 19 publications

Zinc‐Tin‐Oxide Buffer Layer and Low Temperature Post Annealing Resulting in a 9.0% Efficient Cd‐Free Cu₂ZnSnS₄ Solar Cell

Zinc‐Tin‐Oxide Buffer Layer and Low Temperature Post Annealing Resulting in a 9.0% Efficient Cd‐Free Cu₂ZnSnS₄ Solar Cell

Back and front contacts in kesterite solar cells: state-of-the-art and open questions

Optical properties of Cu2ZnSn(SxSe1-x)4 solar absorbers: Spectroscopic ellipsometry and ab initio calculations

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Surface modification through air annealing Cu2ZnSn(S,Se)4 absorbers

Cited by 33 publications

References 19 publications

Zinc‐Tin‐Oxide Buffer Layer and Low Temperature Post Annealing Resulting in a 9.0% Efficient Cd‐Free Cu2ZnSnS4 Solar Cell

Zinc‐Tin‐Oxide Buffer Layer and Low Temperature Post Annealing Resulting in a 9.0% Efficient Cd‐Free Cu2ZnSnS4 Solar Cell

Back and front contacts in kesterite solar cells: state-of-the-art and open questions

Optical properties of Cu2ZnSn(SxSe1-x)4 solar absorbers: Spectroscopic ellipsometry and ab initio calculations

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Product

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Zinc‐Tin‐Oxide Buffer Layer and Low Temperature Post Annealing Resulting in a 9.0% Efficient Cd‐Free Cu₂ZnSnS₄ Solar Cell

Zinc‐Tin‐Oxide Buffer Layer and Low Temperature Post Annealing Resulting in a 9.0% Efficient Cd‐Free Cu₂ZnSnS₄ Solar Cell