Nanoscale Characterization of Back Surfaces and Interfaces in Thin-Film Kesterite Solar Cells

Sardashti, Kasra; Chagarov, Evgueni; Antunez, Priscilla D.; Gershon, Talia; Ueda, Scott T.; Gokmen, Tayfun; Bishop, Douglas M.; Haight, Richard; Kummel, Andrew C.

doi:10.1021/acsami.7b01838

Cited by 18 publications

(12 citation statements)

References 63 publications

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“…For example the formation of n‐type MoS 2 was revealed by a XPS/UPS study performed on the Mo/MoS 2 interface produced by the sulfurization of a Mo film . On the contrary, a strong p‐type doping of Mo(S,Se) 2 was found by Kelvin probe force microscopy measurements performed on a sloped cross‐section of a CZTSSe solar cell …”

Section: Resultsmentioning

confidence: 99%

“…[55] On the contrary, a strong p-type doping of Mo(S,Se) 2 was found by Kelvin probe force microscopy measurements performed on a sloped cross-section of a CZTSSe solar cell. [56] To explain the aging effect, a change in the MoS 2 or MoS 2 / CZTS interface properties should be assumed. In principle, this could be due to diffusion of atomic species (as Na or Cu) but further investigation are required to verify this hypothesis.…”

Section: Analysis Of Blocking Behavior In J-v Curvesmentioning

confidence: 99%

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Cation Disorder In Cu₂ZnSnS₄Thin Films: Effect On Solar Cell Performances

2017

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High (300 °C) and low (160 °C) temperature post deposition annealing treatments are performed on Cu2ZnSnS4 (CZTS) thin film solar cells to modify the order degree of the CZTS absorber and investigate its effect on the device performances. Large and reversible changes of solar cell parameters are observed, with photovoltaic conversion efficiencies varying from about 4% in the case of more ordered materials, up to nearly 8% after the disordering treatment. Both spectrophotometry and photoluminescence reveal that the ordered materials are characterized by a higher bandgap and a lower deep defect density, whereas the absorption tails and the red shift of the luminescence peak compared to the bandgap are found to be independent of the ordering level. Coherently with the bandgap variation, solar cells in the ordered state are characterized by a lower short circuit current density and a higher open circuit voltage. Ordered devices are found to be limited by low fill factor values, often associated with anomalous “S‐shaped” light J–V curves revealing a blocking behavior. A mechanism based on the increase of a blocking barrier at the CZTS/MoS2 back interface induced by a change in the valence band offset is proposed to explain the lower performances of the ordered devices.

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Section: Resultsmentioning

confidence: 99%

Section: Analysis Of Blocking Behavior In J-v Curvesmentioning

confidence: 99%

Cation Disorder In Cu₂ZnSnS₄Thin Films: Effect On Solar Cell Performances

2017

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“…The presence of an n-type or slightly p-doped semiconductor at the back contact may explain the reverse diode sometimes observed in the device characteristics [71,78]. Mo(S, Se) 2 can indeed exhibit both p-type [79,80] and n-type [72,73,81,82] conductivity. The latter case was generally attributed to chalcogen deficiencies [79] even if the n-type behavior of MoS 2 due to S vacancies has been recently revised [83].…”

Section: Electrical Properties Of the Back Contactmentioning

confidence: 98%

“…However, these efforts did not lead to device improvement as seen in table 1. Finally, recent works [13,80] show that for reduced absorber thicknesses, replacing the Mo/Mo(S, Se) 2 back contact with a high work function material (MoO 3 ) can significantly improve the device performance (table 1), but necessitates an exfoliation step of the absorber.…”

Section: Electrical Properties Of the Back Contactmentioning

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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“…CZTSSe solar cell has already achieved 12.6% record efficiency based on molybdenum substrate [7]. The device performance depends on several factors, including the quality of the absorber, band alignment, and back contact characteristics [8][9][10]. The quality of CZTSSe absorber is influenced by various parameters, including annealing condition, precursor film composition, and elemental gradient of precursor film (such as stacking order in the case of vacuum-based deposition) [11][12][13][14].…”

Section: Introductionmentioning

confidence: 99%

Highly efficient Cu2ZnSn(S,Se)4 bifacial solar cell via a composition gradient strategy through the molecular ink

Khan

Huang

et al. 2021

Sci. China Mater.

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The use of transparent conducting oxide (TCO) as a substrate in Cu 2 ZnSn(S,Se) 4 (CZTSSe) thin-film solar cells allows for advanced applications, such as bifacial, semitransparent, and tandem solar cells with the capability to increase power density generation. However, the efficiency of this kind of solar cell is still below 6% based on the low-cost solution process. In this work, we develop a composition gradient strategy and demonstrate a 6.82% efficient CZTSSe solar cell on F:SnO 2 (FTO) substrate under the ambient condition. The composition gradient is realized by simply depositing the precursor inks with different Zn/Sn ratios. To verify that the high performance of the solar cell is attributed to the composition gradient strategy rather than the sole change of the Zn/Sn ratio, devices based on absorbers with varied Zn/Sn ratios are fabricated. Furthermore, the structure and surface morphology of the CZTSSe films with/without composition gradients are examined. The presence of elemental gradient through the depth of the CZTSSe films before and after annealing is confirmed by secondary ion mass spectroscopy analysis. It is found that the composition gradient enhances the crystallinity of the absorber, reduces the surface roughness as well as device parasitic losses, contributing to a higher fill factor, open-circuit voltage , and conversion efficiency.

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Nanoscale Characterization of Back Surfaces and Interfaces in Thin-Film Kesterite Solar Cells

Cited by 18 publications

References 63 publications

Cation Disorder In Cu₂ZnSnS₄Thin Films: Effect On Solar Cell Performances

Cation Disorder In Cu₂ZnSnS₄Thin Films: Effect On Solar Cell Performances

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

Highly efficient Cu2ZnSn(S,Se)4 bifacial solar cell via a composition gradient strategy through the molecular ink

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Nanoscale Characterization of Back Surfaces and Interfaces in Thin-Film Kesterite Solar Cells

Cited by 18 publications

References 63 publications

Cation Disorder In Cu2ZnSnS4Thin Films: Effect On Solar Cell Performances

Cation Disorder In Cu2ZnSnS4Thin Films: Effect On Solar Cell Performances

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

Highly efficient Cu2ZnSn(S,Se)4 bifacial solar cell via a composition gradient strategy through the molecular ink

Contact Info

Product

Resources

About

Cation Disorder In Cu₂ZnSnS₄Thin Films: Effect On Solar Cell Performances

Cation Disorder In Cu₂ZnSnS₄Thin Films: Effect On Solar Cell Performances