Deposition and characterization of spray pyrolysed p-type Cu2SnS3 thin film for potential absorber layer of solar cell

doi:10.1016/j.physb.2018.03.007

Physica B: Condensed Matter

Volume 538, 1 June 2018, Pages 8-12

https://doi.org/10.1016/j.physb.2018.03.007 Get rights and content

Highlights

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Cu₂SnS₃ (CTS) thin film deposited at 573 K by chemical spray pyrolysis.
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Tetragonal CTS structure confirmed by GIXRD pattern and Micro-Raman analysis.
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AFM was used to study the grain size and surface roughness of deposited thin film.
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Optical band gap of CTS thin film is found to be 1.70 eV.
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Hall effect revealed CTS thin film having p-type conduction.

Abstract

Thin film of ternary Cu₂SnS₃ (CTS), a potential absorber layer for solar cells was successfully deposited by chemical spray pyrolysis technique. The GIXRD pattern revealed that the film having tetragonal Cu₂SnS₃ phase with the preferential orientation along (112), (200), (220) and (312) plane and it is further confirmed using Raman spectroscopy by the existence of Raman peak at 320 cm⁻¹. Atomic Force Microscopy (AFM) was used to estimate the surface roughness of 28.8 nm. The absorption coefficient was found to be greater than the order of 10⁵ cm⁻¹ and bandgap of 1.70 eV. Hall effect measurement indicates the p type nature of the film with a hole concentration of 1.03 × 10¹⁶cm⁻³ and a hall mobility of 404 cm²/V. The properties of CTS thin film confirmed suitable to be a potential absorber layer material for photovoltaic applications.

Introduction

In recent years, the ternary metal chalcogenide materials have shown great potential candidates for the application of thin film solar cells due to their band gap energy, large absorption coefficient and good photo-stability [1]. Recently, quaternary Cu₂ZnSnS₄ (CZTS) has attracted more attention because of its non-toxicity and abundant elements [2] but the composition of quaternary CZTS is difficult to control [3]. Hence, the ternary compound consisting of abundant elements [4], which is expected to be deposited easier than quaternary CZTS and their properties for the photovoltaic applications, should be investigated. At present, p-type Cu₂SnS₃ (CTS) has received significant attention as a suitable material for thin film solar cells because of its high optical absorption coefficient (∼10⁴cm⁻¹), band gap energy and consisting abundant materials [5]. CTS is also a compound which consists of extremely low toxicity materials and abundant in the earth's crust. CTS have been reported to have a band gap energy range from 0.93 to 1.77 eV and to crystallize in a tetragonal, cubic sphalerite-like phase or in the monoclinic structure, with a sphalerite superstructure [6]. In the year 1987, first time Kuku et al. reported the optical absorption and photovoltaic characteristics of thin films of Cu₂SnS₃ [7]. They reported that the films obtained by the direct evaporation of the synthesized compound were copper deficient, while those grown in an ambiance of copper vapor to be more stoichiometric. In recent past, CTS have been deposited by different deposition techniques such as co-evaporation [[8], [9], [10], [11], [12]], co-sputtering [13], Pulsed laser deposition [14], thermal evaporation with sulfurization [[15], [16], [17]], electron beam evaporation [[18], [19], [20]], sputtering [[21], [22], [23]], electrodeposition [24,25], and chemical methods like spray pyrolysis [7,[26], [27], [28], [29], [30], [31]], SILAR [32], spin coating [33], and dip coating [34]. The efficiency is quite low compared with its quaternary materials and hence it requires more systematic studies to improve the efficiency of CTS thin film for solar cell applications.

Chemical spray pyrolysis is a flexible and cost-effective deposition technique, which is extensively used to deposit ternary semiconductor thin films. In 2007, Bouaziz et al. [26] successfully deposited p-type copper tin sulphide films by a spray pyrolysis technique with the band gap of 1.22 eV. Again in 2009 [27], they fabricated CTS thin films with band gap of 1.15 eV by superposition of SnS₂ and Cu_xS on Pyrex substrates followed sulfur annealing process. In 2012, Adelifard et al. [28] deposited CTS thin films with different Sn/Cu molar ratios and found that the Sn/Cu ratio increased significant improvement in roughness and grain morphology, especially in the Sn-rich layers. In the same year, Chalapathi et al. [29] deposited Cu₂SnS₃ thin films onto soda lime glass substrates by spray pyrolysis technique at a substrate temperature of 360 °C and CuS as the minor phase which was eliminated by KCN etching. The films were slightly Cu-rich and S-poor with the direct optical band gap of 1.42 eV. Again in 2013 [30], Cu₂SnS₃ thin films are deposited at 360 °C and annealing in sulphur atmosphere at 400, 450 and 500 °C. Films annealed at 500 °C were found monoclinic CTS phase with the bandgap of 1.1 eV while as-deposited films and films annealed at lower temperatures were found tetragonal CTS phase with the bandgap of 0.97 eV. In 2015, Jia et al. [31] studied the influences of Cu precursor concentration and substrate temperature on the properties of sprayed CTS film. The substrate temperature of 350 °C, Cu concentration in precursor solution of 0.02 M has the best crystallinity and the band gap value was 1.16 eV. In the present paper, ternary Cu₂SnS₃ thin film was deposited by chemical spray pyrolysis technique and the structural, morphological, optical and electrical properties of spray deposited CTS thin film was examined by employing GIXRD, Micro-Raman, AFM, UV and Hall measurements.

Section snippets

Sample preparation

CTS thin film was deposited by the chemical spray pyrolysis technique on soda lime glass substrates using the aqueous solution containing the precursors such as cupric chloride (5 milli-mol/L), tin chloride (5 milli-mol/L) and thiourea (20 milli-mol/L). The substrate temperature was kept at 573 K with an accuracy of ±5 K using digital temperature controller. The chemical reaction is as follows $2 CuCl (aq) + {SnCl}_{4} (aq) + 3 SC {({NH}_{2})}_{2} (aq) + {6 H}_{2} O (l) \overset{573 K}{\to} {Cu}_{2} {SnS}_{3} (s) + 3 {CO}_{2} (g) + {6 NH}_{3} (g) + 6 HCl (g)$

The precursor solution

GIXRD characterization

The GIXRD pattern of spray deposited CTS thin film is shown in Fig. 1 and it is found to be well matched with the pattern of tetragonal CTS phase. The peaks located at 28.54, 33.07, 47.47 and 56.32 corresponding to the (112), (200), (220) and (312) planes could be attributed for the characteristics of tetragonal CTS system [35]. Furthermore, the pattern shows that the additional peaks along (203), (211) and (104) direction which confirms the secondary phase Sn₂S₃ and the planes (110), (108) and

Conclusion

CTS thin film was successfully deposited on to sodalime glass substrate by chemical spray pyrolysis technique and the properties were investigated by GIXRD, micro-Raman, AFM, UV–Vis spectrophotometer and Hall measurement. The GIXRD pattern exhibited tetragonal structure with preferential orientation along (112) direction for CTS thin film and it's confirmed by micro-Raman spectral peak at 320 cm⁻¹ for the existence of Cu₂SnS₃ with few binary phases. The absorption coefficient of CTS thin film

Acknowledgment

The authors would like to thank UGC-DAE CSR, Indore and Kalpakkam Node, for providing various characterization facilities and we are also thankful to Dr. M. C. Santhosh Kumar, Department of Physics, National Institute of Technology, Tiruchirappalli for providing Hall measurement.

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Deposition and characterization of spray pyrolysed p-type Cu2SnS3 thin film for potential absorber layer of solar cell

Highlights

Abstract

Introduction

Section snippets

Sample preparation

GIXRD characterization

Conclusion

Acknowledgment

Sol. Energy

Physica B

Sol. Energy Mater. Sol. Cells

Acta Mater.

Sol. Energy Mater.

Vacuum

J. Alloy Compd

Vacuum

Sol. Energy Mater. Sol. Cells

Thin Solid Films

J. Alloy Compd

Thin Solid Films

Thin Solid Films

Vacuum

Sol. Energy Mater. Sol. Cells

J. Colloid Interface Sci.

Angew. Chem.

Phys. Scr

Jap. J. Appl. Phys.

Sol. Energy Mater. Sol. Cells

Deposition and characterization of spray pyrolysed p-type Cu₂SnS₃ thin film for potential absorber layer of solar cell