Synthesis and characterization of Cu2ZnSnS4 thin films by SILAR method

doi:10.1016/j.jpcs.2012.01.008

Journal of Physics and Chemistry of Solids

Volume 73, Issue 6, June 2012, Pages 735-740

https://doi.org/10.1016/j.jpcs.2012.01.008 Get rights and content

Abstract

Semiconducting Cu₂ZnSnS₄ (CZTS) material has been receiving a great technological interest in the photovoltaic industry because of its low-cost non-toxic constituents, ideal direct band gap as a absorber layer and high absorption coefficient. CZTS thin films have been successfully deposited onto the fluorine-doped tin oxide/glass (glass/FTO) substrates coated glass substrates using successive ionic layer adsorption and reaction (SILAR) method and investigated for photoelectrochemical conversion (PEC) of light into electricity. The best solar cell sample showed an open-circuit voltage of 390 mV, a short-circuit current density of 636.9 μA/cm², a fill factor of 0.62 and an efficiency of 0.396% under irradiation of 30 mW/cm². Preliminary results obtained for solar cells fabricated with this material are promising.

Graphical Abstract

Highlights

► Cu₂ZnSnS₄ thin films by successive ionic layer adsorption and reaction (SILAR). ► Photoelectrochemical (PEC) conversion application. ► CZTS power conversion efficiency 0.396%.

Introduction

Commercial impact of second generation photovoltaic devices employing copper indium diselenide (CIS) based alloys as absorber materials is limited by the cost and toxicity of indium. At this juncture, a p-type Cu₂ZnSnS₄ (CZTS), a I₂–II–IV–VI₄ quaternary compound semiconductor can be used as a potential alternative absorber layer in thin film solar cells to expensive CIS, wherein ternary CIS compound selenium (Se) is substituted with sulfur (S), the rare metal indium (In) with zinc (Zn) and tin (Sn). All the constituents required for CZTS synthesis are low-cost, abundantly available in the earth crust and are notably non-toxic. CZTS exhibits a stannite-type structure. Because of high optical absorption coefficient (>10⁴ cm⁻¹) and an ideal direct band gap (1.4–1.5 eV), CZTS has been regarded as one of the most promising materials for light-harvesting materials in solar cells [1], [2], [3], [4].

Initial report on CZTS is by Katagiri and co-workers, who used inline vacuum sputtering of Cu, SnS and ZnS followed by annealing in a 5% H₂S in N₂ atmosphere for 1 h at 550 °C [5], [6]. Power conversion efficiencies as high as 6.77% have been obtained using solar cells based on CZTS under AM1.5G illumination [7]. However, theoretical limit for CZTS is reported to be 32.2% [8]. Various other methods have also been employed to prepare CZTS thin films including electron beam evaporation [9], [10], pulsed laser deposition (PLD) [11], [12], electrodeposition of metallic precursors followed by annealing in sulfur vapor [10b,[13], [14], [15], [16],18], RF magnetron sputtering [19], DC magnetron sputtering [20], spray pyrolysis technique [21], [22], [23], sol–gel method [24], [25] precipitation reaction in hot organic solutions [26] and aqueous bath process [27]. Wada et al. developed the method to deposit the CIGS thin films by mechanochemical and screen-printing technique under non-vacuum condition in an attempt to make it cost-effective, however, it required post annealing treatment [28]. A successive ionic layer adsorption and reaction (SILAR) method is one of the chemical methods for making uniform and large area thin films, which is based on immersion of the substrate into separately placed cations and anions. The SILAR method has been successfully employed for many metal sulfides, selenides, tellurides including oxides. Compared with other film deposition techniques, the distinguished merits of SILAR are the low deposition temperature, the application of aqueous solution, the layer-by-layer growing feature, and the separate anionic and cationic source. A simple solution based SILAR method has not yet been employed to synthesize a technologically important CZTS material. To the best of author's knowledge, there are hardly any reports on the preparation of solar cells with CZTS absorber layers deposited by SILAR method.

Here, we report the first time synthesis of CZTS thin film by a simple wet chemistry method known as SILAR, which facilitates growth of CZTS thin films by repeating a sequential immersion of the substrate in the solutions of cationic (Cu²⁺, Zn²⁺, Sn²⁺) and anionic (S²⁻) precursors. As-deposited films were dried in oven at 60 °C for 30 min. The structural, morphological, compositional and optical properties of the CZTS thin films have been investigated. The photoelectrochemical (PEC) properties of the resulting electrode as a function of the repeating cycles (film thickness) used in the CZTS synthesis are investigated.

Section snippets

Experimental

Analytical reagent grade (AR) chemicals were used for preparation of chemical baths. Before the deposition of CZTS thin films, glass slides were cleaned with detergent and distilled water, then boiled in chromic acid (0.5 M) for 15 min, then slides washed with double distilled water and further ultrasonicated for 15 min. Finally the substrates were degreased in AR grade acetone and used for deposition. The preparative parameters, including precursor concentration, dipping time and number of

Results and discussion

The optical absorption spectra for all the CZTS samples were recorded in the wavelength range of 350–800 nm at room temperature. In order to confirm the nature of optical transition in all samples, the optical data were analyzed using classical absorption equation: $α = \frac{α_{0} {(h ν - E_{g})}^{n}}{h ν}$ where α₀ is a constant, hν is the incident photon energy, E_g is the separation between bottom of conduction band and top of the valence band and n is the constant. For allowed direct transition, n=1/2, and for allowed

Conclusions

In conclusion, we have successfully synthesized the non-toxic Cu₂ZnSnS₄ (CZTS) thin films by successive ionic layer adsorption and reaction (SILAR) method. In order to optimize the synthesis conditions of these films, the dipping time was 30 s in each precursor of constituents and the dipping cycles were varied from 10 to 40.

The synthesized CZTS thin films were characterized by different techniques. CZTS films exhibited a quite smooth, dense and uniform topography on soda lime glass substrate.

Acknowledgment

The one of the author SSM wish to acknowledge the DAE-BRNS Mumbai for financial support through DEA-BRNS project no. 2008/37/8/BRNS/1489 during 2008–2012.

References (28)

T. Tanaka et al.
Preparation of Cu₂ZnSnS₄ thin films by hybrid sputtering
J. Phys. Chem. Solids
(2005)
J.S. Seol et al.
Electrical and optical properties of Cu₂ZnSnS₄ thin films prepared by rf magnetron sputtering process
Sol. Energy Mater. Sol. Cells
(2003)
H. Katagiri et al.
Development of CZTS-based thin film solar cells
Thin Solid Films
(2009)
H. Araki et al.
Preparation of Cu₂ZnSnS₄ thin films by sulfurization of stacked metallic layers
Thin Solid Films
(2008)
O. Volobujeva et al.
Cu₂ZnSnSe₄ films by selenization of Sn–Zn–Cu sequential films
J. Phys. Chem. Solids
(2009)
J.J. Scragg et al.
Synthesis and characterization of Cu₂ZnSnS₄ absorber layers by an electrodeposition-annealing route
Thin Solid Films
(2009)
A.V. Moholkar et al.
Development of CZTS thin films solar cells by pulsed laser deposition: Influence of pulse repetition rate
Sol. Energy
(2011)
A.V. Moholkar et al.
Synthesis and characterization of Cu₂ZnSnS₄ thin films grown by PLD: solar cells
J. Alloys Compd.
(2011)
J.J. Scragg et al.
Towards sustainable materials for solar energy conversion: preparation and photoelectrochemical characterization of Cu₂ZnSnS₄
Electrochem. Commun.
(2008)
S.M. Pawar et al.
Single step electrosynthesis of Cu₂ZnSnS₄ (CZTS) thin films for solar cell application
Electrochim. Acta
(2010)
J.J. Scragg et al.
A 3.2% efficient Kesterite device from electrodeposited stacked elemental layers
J. Electroanal. Chem.
(2010)

H. Araki et al.

Preparation of Cu₂ZnSnS₄ thin films by sulfurizing electroplated precursors

Sol. Energy Mater. Sol. Cells

(2009)

R. Schurr et al.

The crystallisation of Cu₂ZnSnS₄ thin film solar cell absorbers from co-electroplated Cu–Zn–Sn precursors

Thin Solid Films

(2009)

R.A. Wibowo et al.

Single step preparation of quaternary Cu₂ZnSnSe₄ thin films by RF magnetron sputtering from binary chalcogenide targets

J. Phys. Chem. Solids

(2007)

P.A. Fernandes et al.

Growth and Raman scattering characterization of Cu₂ZnSnS₄ thin films

Thin Solid Films

(2009)

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Citation Excerpt :
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Synthesis and characterization of Cu2ZnSnS4 thin films by SILAR method

Abstract

Graphical Abstract

Highlights

Introduction

Section snippets

Experimental

Results and discussion

Conclusions

Acknowledgment

J. Phys. Chem. Solids

Sol. Energy Mater. Sol. Cells

Thin Solid Films

Thin Solid Films

J. Phys. Chem. Solids

Thin Solid Films

Sol. Energy

J. Alloys Compd.

Electrochem. Commun.

Electrochim. Acta

J. Electroanal. Chem.

Sol. Energy Mater. Sol. Cells

Thin Solid Films

J. Phys. Chem. Solids

Thin Solid Films

Synthesis and characterization of Cu₂ZnSnS₄ thin films by SILAR method