Cadmium Free Cu<sub>2</sub>ZnSnS<sub>4</sub> Solar Cells with 9.7% Efficiency

Larsen, Jes K.; Larsson, Frederik; Törndahl, Tobias; Saini, Nishant; Riekehr, Lars; Ren, Yi; Biswal, Adyasha; Hauschild, Dirk; Weinhardt, L.; Heske, Clemens; Platzer‐Björkman, Charlotte

doi:10.1002/aenm.201900439

Cited by 81 publications

(61 citation statements)

References 44 publications

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“…In our case, the graded composition after 2 and 6 min is accompanied by a large‐grained top layer and a small‐grained bottom layer. It remains to be investigated if such back‐layer morphology is detrimental to the device performance, but we note that short annealing for 1 min of CZTS has led to higher voltage and efficiency as compared with 13 min annealing using our process, despite the smaller grains . This implies that the short annealing times needed here to maintain a Ge/Sn gradient can be compatible with, and even advantageous for, obtaining good device performance.…”

Section: Discussionmentioning

confidence: 86%

Germanium Incorporation in Cu₂ZnSnS₄ and Formation of a Sn–Ge Gradient

Saini

Larsen

Sopiha

et al. 2019

Physica Status Solidi (a)

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Alloying of Cu2ZnSnS4 (CZTS) with Ge can potentially promote grain growth and suppress the formation of Sn‐related defects. Herein, a two‐step fabrication route based on compound co‐sputtering and sulfurization at a high temperature is used to prepare Ge‐incorporated CZTS (Cu2ZnGexSn1 − xS4 [CZGTS]). For Cu2ZnGeS4 (CZGS), films deposited using elemental Ge and binary GeS targets are compared. The recrystallization is shown to be promoted for the absorbers deposited using Ge target, possibly due to lower sulfur content in the precursor suppressing the formation of wurtzite‐like phases during sputtering. The grain growth and crystallinity in CZGTS are slightly improved for x = 0.2 but not for higher concentration of the incorporated Ge. Owing to the composition‐dependent electronic properties, compositionally graded CZGTS films may be beneficial for reducing recombination towards the back contact. Hence, herein, the successful formation of a steep concentration gradient with Ge and Sn is demonstrated by the deposition of a CZGS/CZTS precursor stack followed by sulfurization with varying time periods.

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Section: Discussionmentioning

confidence: 86%

Germanium Incorporation in Cu₂ZnSnS₄ and Formation of a Sn–Ge Gradient

Saini

Larsen

Sopiha

et al. 2019

Physica Status Solidi (a)

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“…The annealing period was 13 minutes; this corresponds to our baseline annealing process used to achieve CZTS solar cells with 9.7% efficiency. 28 The next sample (B) was annealed in the same way but for only two minutes. For samples A and B, the chemical potential of S (dened by its partial pressure 29 ) will evolve along the same curve, with partial pressure dropping with time due to leakage from the box.…”

Section: Experimental Methodsmentioning

confidence: 99%

Prospects for defect engineering in Cu₂ZnSnS₄ solar absorber films

et al. 2020

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“…Similar improvement was also obtained by Li et al [108] for CZTSSe-based TFSCs with a PCE of 8.6% as compared to 8.14% PCE for the CdS-buffer device. The highest efficiency using ALD Zn 1−x Sn x O y buffers for CZTS of 9.7% was reported by Larsen et al [118]. In that study, solar cells based on ordered CZTS were compared to devices made from non-ordered CZTS.…”

Section: Zn 1−x Sn X O Y Buffer Layersmentioning

confidence: 97%

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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Cadmium Free Cu₂ZnSnS₄ Solar Cells with 9.7% Efficiency

Abstract: Access to the published version may require subscription. N.B. When citing this work, cite the original published paper.

Cited by 81 publications

References 44 publications

Germanium Incorporation in Cu₂ZnSnS₄ and Formation of a Sn–Ge Gradient

Germanium Incorporation in Cu₂ZnSnS₄ and Formation of a Sn–Ge Gradient

Prospects for defect engineering in Cu₂ZnSnS₄ solar absorber films

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

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Cadmium Free Cu2ZnSnS4 Solar Cells with 9.7% Efficiency

Abstract: Access to the published version may require subscription. N.B. When citing this work, cite the original published paper.

Cited by 81 publications

References 44 publications

Germanium Incorporation in Cu2ZnSnS4 and Formation of a Sn–Ge Gradient

Germanium Incorporation in Cu2ZnSnS4 and Formation of a Sn–Ge Gradient

Prospects for defect engineering in Cu2ZnSnS4 solar absorber films

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

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Cadmium Free Cu₂ZnSnS₄ Solar Cells with 9.7% Efficiency

Germanium Incorporation in Cu₂ZnSnS₄ and Formation of a Sn–Ge Gradient

Germanium Incorporation in Cu₂ZnSnS₄ and Formation of a Sn–Ge Gradient

Prospects for defect engineering in Cu₂ZnSnS₄ solar absorber films