Cation Disorder In Cu<sub>2</sub>ZnSnS<sub>4</sub>Thin Films: Effect On Solar Cell Performances

Malerba, Claudia; Valentini, Matteo; Mittiga, A.

doi:10.1002/solr.201700101

Cited by 41 publications

(48 citation statements)

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“…The Mo(S, Se) 2 conductivity is also under debate. 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.…”

Section: Electrical Properties Of the Back Contactmentioning

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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Section: Electrical Properties Of the Back Contactmentioning

confidence: 97%

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

et al. 2019

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“…Compared to previous annealing experiments performed in a tubular furnace using a semi-closed chamber (not published), the optimized annealing system allows to produce devices with an improved CZTS/CdS junction quality (without any hazardous chemical etching, like those based on KCN), as demonstrated by reverse saturation current densities as low as a few nA cm −2 [24]. Even in this case, the efficiency progress cannot be simply ascribed to the optimization of the growth process, but also to a strong beneficial effect of PDA treatment performed on complete devices [24]. Physical mechanisms underlying the PDA effects are discussed in another paper of this journal issue.…”

Section: Sequential Sputtering/co-sputteringmentioning

confidence: 99%

“…The main difference between these two approaches is the chalcogen amount in the starting precursor, which is close to the stoichiometric amount in case of CuS, SnS and ZnS targets and it is lower when one or more binary compounds are replaced by the pure elemental targets. Both approaches were proven to give successful results, with a recent efficiency record of 11.04% [5] and many groups reporting devices with efficiency close or higher than 8% [22][23][24].…”

Section: Sequential Sputtering/co-sputteringmentioning

confidence: 99%

“…This latter point is particularly important for CZTS devices because of the well-known notoptimum band alignment between CZTS and CdS [79,80]. Moreover, PDA treatments, performed either on the bare absorber [81] or on the CZTS/CdS samples [5] or even on complete devices [24] have been also proven to boost efficiencies. All these points must be taken into account when device performances are compared since, often in this framework, the efficiency is not a measure of the quality of the growth process alone.…”

Section: Sequential Sputtering/co-sputteringmentioning

confidence: 99%

“…In the same year, a device with an efficiency 7.94% was produced by the ENEA group [24] using a Cu-SnS-ZnS co-sputtered precursor, annealed for 1 h in a mixed N 2 -S atmosphere, under gas flow conditions, using a custom system with two independent chambers for the precursors (at about 570 • C; heating rate 20 • C min −1 ) and for the sulfur source (at about 260 • C). The sputtering process was carried out without any intentional heating of the substrate and at a working pressure of 5×10 −3 mbar, optimized to improve the adhesion of the final CZTS film on the substrate.…”

Section: Sequential Sputtering/co-sputteringmentioning

confidence: 99%

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Physical routes for the synthesis of kesterite

et al. 2019

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This paper provides an overview of the physical vapor technologies used to synthesize Cu 2 ZnSn(S,Se) 4 thin films as absorber layers for photovoltaic applications. Through the years, CZT(S,Se) thin films have been fabricated using sequential stacking or co-sputtering of precursors as well as using sequential or co-evaporation of elemental sources, leading to high-efficient solar cells. In addition, pulsed laser deposition of composite targets and monograin growth by the molten salt method were developed as alternative methods for kesterite layers deposition. This review presents the growing increase of the kesterite-based solar cell efficiencies achieved over the recent years. A historical description of the main issues limiting this efficiency and of the experimental pathways designed to prevent or limit these issues is provided and discussed as well. A final section is dedicated to the description of promising process steps aiming at further improvements of solar cell efficiency, such as alkali doping and bandgap grading. intensive research on Cu 2 ZnSn(S,Se) 4 (CZT(S,Se)) kesterite compounds as CRM-free absorber layers for PV applications is essential. This article aims at establishing a complete overview of the physical routes used for the synthesis of kesterite thin films as absorber layers in solar cells. The following sections are devoted to that objective and will take on the main issues which have been raised so far as well as how the processes have evolved through the years to meet the requirements of the market. Some major advancements in terms of deposition or post-deposition treatments are introduced. Advantages and drawbacks of each of the physical methods presented in this review are described in detail and compared to other physical or chemical synthesis routes. Physical routes: status overviewWe performed an extensive identification of the common processes and methods used for the synthesis of kesterite thin films or for the design of solar cell devices. In order to avoid unnecessary repetitions along this paper, this section first explains these well-known and commonly used experimental processes and methods. Historically, based on the similarities between kesterite and chalcopyrite compounds, the standard device structure adopted for Cu(In,Ga)(S,Se) 2 (CIGSSe) was directly extended to CZTSSe, by simply replacing the CIGSSe absorber layer with a p-type CZTSSe thin film. CZTSSe solar cells are then typically produced using a soda-lime glass (SLG) substrate coated with a sputtered Mo layer acting as rear metallic contact. Typical sputter-deposited Mo layer thickness is around 500 nm up to 1 μm [12]. The kesterite absorber is then deposited onto the Mo layer.The fabrication of this absorber consists in the deposition of a precursor layer via a physical or a chemical route, which is then annealed in a reactive atmosphere containing either S (sulfurization) or Se (selenization). As a common result of the reactive annealing, a thin Mo(S,Se) 2 layer is naturally formed at the CZTSSe/Mo interface, betw...

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Defect Engineering for Efficient Cu₂ZnSnS₄ Solar Cells via Moisture‐Assisted Post‐Deposition Annealing

Sun

Huang

Young

et al. 2022

Advanced Optical Materials

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Sulfide kesterite Cu2ZnSnS4 (CZTS) solar cells, containing earth‐abundant and environmentally benign constituents, are regarded as promising candidates for thin‐film photovoltaic technologies. CZTS device performance, however, is currently limited by severe nonradiative recombination caused by abundant deep‐level defects. Herein, an effective defect engineering approach for high bandgap CZTS solar cells using a newly introduced moisture‐assisted post‐deposition annealing treatment is reported. This treatment modifies the local chemical composition within the heterojunction and CZTS grain boundaries and enhances the incorporation of Cd within the CZTS layer during CdS deposition. Cd not only accumulates at the grain boundaries, but it also presents in grain interiors where it occupies Cu lattice sites. The overall modification of the local chemical environment suppresses deep level defects and activates relatively shallow acceptor CuZn antisites and Cu vacancies, giving rise to remarkably improved device performance. This work opens a new direction for defect engineering of kesterite materials, which may also be applicable to other thin film semiconductors.

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Cation Disorder In Cu₂ZnSnS₄Thin Films: Effect On Solar Cell Performances

Cited by 41 publications

References 56 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

Physical routes for the synthesis of kesterite

Defect Engineering for Efficient Cu₂ZnSnS₄ Solar Cells via Moisture‐Assisted Post‐Deposition Annealing

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Cation Disorder In Cu2ZnSnS4Thin Films: Effect On Solar Cell Performances

Cited by 41 publications

References 56 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

Physical routes for the synthesis of kesterite

Defect Engineering for Efficient Cu2ZnSnS4 Solar Cells via Moisture‐Assisted Post‐Deposition Annealing

Contact Info

Product

Resources

About

Cation Disorder In Cu₂ZnSnS₄Thin Films: Effect On Solar Cell Performances

Defect Engineering for Efficient Cu₂ZnSnS₄ Solar Cells via Moisture‐Assisted Post‐Deposition Annealing