TiN Interlayers with Varied Thickness in Cu<sub>2</sub>ZnSnS(e)<sub>4</sub> Thin Film Solar Cells: Effect on Na Diffusion, Back Contact Stability, and Performance

Englund, Sven; Grini, Sigbjørn; Donzel‐Gargand, Olivier; Paneta, V.; Kosyak, V.; Primetzhofer, Daniel; Scragg, Jonathan J.; Platzer‐Björkman, Charlotte

doi:10.1002/pssa.201800491

Cited by 16 publications

(9 citation statements)

References 40 publications

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“…An alternative explanation is based on the aforementioned likelihood of defects such as pinholes in thin interlayers. Such features have indeed been observed for sputtered TiN [63] and Al 2 O 3 [26] interlayers used for CZTS(e) back contacts. Thus, it is also possible that while the interlayer prevents S(e) from diffusing to most of the back contact, Na is able to diffuse via pinholes/cracks in the interlayer and spread into the CZTS(e) layer from there.…”

Section: Protective Interlayers At the Back Contactsupporting

confidence: 59%

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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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Section: Protective Interlayers At the Back Contactsupporting

confidence: 59%

“…For CZTS(e), it seems relatively easy to suppress Mo(S, Se) 2 formation by use of standard Ti-nitride or -boride interlayers [55,63,64], presumably due to reduced S(e) diffusivity in these materials. In this respect, the interlayers appear to act as effective diffusion barriers.…”

Section: Protective Interlayers At 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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“…The substrate holder was rotated at 20 rpm (rotations per minute) to achieve a uniform composition of CZGTS. One substrate was placed in the center of the substrate holder for measurement of elemental composition using XRF . After the deposition of the precursors, the films were sulfurized in a pyrolitic carbon‐coated graphite box with 40 mg sulfur under a pressure of 350 torr Ar at 581 °C for 13 min.…”

Section: Methodsmentioning

confidence: 99%

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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“…In the present study, the samples were deposited on soda‐lime glass (SLG) substrates, which usually act as a source of Na supplied through the back contact to the absorber. Previous studies suggest that the nature of the back contact may affect the diffusion of Na . Therefore, Na profiles of the different samples were measured by glow discharge optical emission spectroscopy (GDOES).…”

Section: Resultsmentioning

confidence: 99%

Antimony‐Doped Tin Oxide as Transparent Back Contact in Cu₂ZnSnS₄ Thin‐Film Solar Cells

Englund

Kubart

Keller

et al. 2019

Physica Status Solidi (a)

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Antimony-doped tin oxide (Sn 2 O 3 :Sb, ATO) is investigated as a transparent back contact for Cu 2 ZnSnS 4 (CZTS) thin-film solar cells. The stability of the ATO under different anneal conditions and the effect from ATO on CZTS absorber growth are studied. It is found that ATO directly exposed to sulfurizing anneal atmosphere reacts with S, but when covered by CZTS, it does not deteriorate when annealed at T < 550 C. The electrical properties of ATO are even found to improve when CZTS is annealed at T ¼ 534 C. At T ¼ 580 C, it is found that ATO reacts with S and degrades. Analysis shows repeatedly that ATO affects the absorber growth as large amounts of SnÀS secondary compounds are found on the absorber surfaces. Time-resolved anneal series show that these compounds form early during anneal and evaporate with time to leave pinholes behind. Device performance can be improved by addition of Na prior to annealing. The best CZTS device on ATO back contact herein has an efficiency of 2.6%. As compared with a reference on a Mo back contact, a similar opencircuit voltage and short-circuit current density are achieved, but a lower fill factor is measured.

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TiN Interlayers with Varied Thickness in Cu₂ZnSnS(e)₄ Thin Film Solar Cells: Effect on Na Diffusion, Back Contact Stability, and Performance

Cited by 16 publications

References 40 publications

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

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

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

Antimony‐Doped Tin Oxide as Transparent Back Contact in Cu₂ZnSnS₄ Thin‐Film Solar Cells

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TiN Interlayers with Varied Thickness in Cu2ZnSnS(e)4 Thin Film Solar Cells: Effect on Na Diffusion, Back Contact Stability, and Performance

Cited by 16 publications

References 40 publications

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

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

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

Antimony‐Doped Tin Oxide as Transparent Back Contact in Cu2ZnSnS4 Thin‐Film Solar Cells

Contact Info

Product

Resources

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TiN Interlayers with Varied Thickness in Cu₂ZnSnS(e)₄ Thin Film Solar Cells: Effect on Na Diffusion, Back Contact Stability, and Performance

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

Antimony‐Doped Tin Oxide as Transparent Back Contact in Cu₂ZnSnS₄ Thin‐Film Solar Cells