Preparation and characterization of Cu2FeSnS4 quaternary semiconductor thin films via the spray pyrolysis technique for photovoltaic applications

doi:10.1016/j.jaap.2016.09.022

Journal of Analytical and Applied Pyrolysis

Volume 122, November 2016, Pages 209-215

https://doi.org/10.1016/j.jaap.2016.09.022 Get rights and content

Highlights

•
P-type Cu₂FeSnS₄ absorber layers were synthesized by a simple chemical spray pyrolysis technique.
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Data analysis revealed pure stannite structure along with nearly stoichiometric in films.
•
High absorption coefficient values close to 10⁵ cm⁻¹ and optimum band gap about 1.50 eV was found.
•
Hall effect data including hole density and their mobilities are presented.

Abstract

The Cu₂FeSnS₄ (CFTS) nanostructured thin films have been spray deposited onto glass substrates without any post-sulfurization in toxic atmosphere such as H₂S or ‘S’ vapor. The influence of substrate temperatures on the structural, morphological, compositional, optical, electrical and photoconductivity properties of the CFTS thin films have been studied. These properties are found to be strongly dependent on the substrate temperature. XRD spectra analysis revealed that all CFTS thin films showing pure stannite structure. The improved crystallinity of the CFTS with a (112) orientation was observed with increasing the substrate temperature. The spray synthesized CFTS films exhibit a smooth, uniform and dense topography. EDS study reveals that the deposited thin films are nearly stoichiometric. The direct band gap energy for the CFTS thin films is found to be about 1.50 eV, which is close to the ideal band gap for the highest theoretical conversion efficiency of solar cell. Electrical conductivity and hole mobility of the CFTS films increases with increasing substrate temperatures. The films were p-type and shows photoconductivity. Electrical measurements (I–V curves) were registered in dark and under light exposure and were correlated with the films composition and structure, as obtained from the EDS analysis and XRD patterns.

Introduction

Currently, researches on low-cost thin film solar cells are increasing significantly. Various types of well-known solar cell materials such as CdTe and CuIn(Ga)Se₂ (CIGS) have been extensively investigated [1], [2], [3], [4], [5]. These materials have the toxicity of cadmium, expensive and scarce elements like indium and gallium, respectively, which affects large-scale production. To achieve the goal of cost-effective photovoltaic technology, it is necessary to explore new materials contains less toxic material S instead of Se and more abundant elements, Fe, Sn, than In, like Cu₂FeSnS₄ (CFTS) and other quaternaries of these chalcopyrite-like semiconductors. CFTS is reported to have a band gap between 1.2 and 1.5 eV (ideal for a single junction solar cell) [6], [7], [8], [9], [10], [11], [12] and a band edge absorption coefficient above 10⁴ cm⁻¹. A thorough understanding of material properties is very much essential for the successful utilization of this compound in solar cells.

Recently, several techniques including physical and chemical methods have been employed for preparing CFTS thin films namely: sputtering [11] and successive ionic layer absorption and reaction [12]. Generally these techniques are multi steps processes, they are based on sequential or co-deposition of precursor metallic stacked layers followed by a subsequent sulfurization. Also, other techniques such as hot injection and the ultrasound-assisted microwave irradiation for the deposition of CFTS layer were utilized [7], [8]. However, the above methods for synthesizing CFTS are usually complex and time-consuming. Considering these problems, for a large scale solar cell production a single step and facile deposition process is more economic and well suitable.

Chemical spray pyrolysis (CSP) technique is low-cost, non-vacuum and eco-friendly, and can be used for cost-effective large-area deposition, with no need of any sophisticated instrumentation. However, to the best of our knowledge, spray deposition of CFTS thin films has rarely been reported. Prabhakar et al. [10] reported deposition of CFTS thin films by spray pyrolysis followed by sulfurization at different temperatures of 400, 500 and 600 °C. The effect of sulfurization temperature on the properties of CFTS thin films was studied.

In this study, we report a simple method to prepare CFTS thin films by spray pyrolysis technique on the glass substrate without sulfurization in toxic atmosphere such as H₂S or ‘S’ vapor. Different substrate temperature conditions (250–370 °C) were used to study the effect of substrate temperature on the structural, compositional, morphological, optical, electrical and photoconductivity properties of CFTS thin films.

Section snippets

Synthesis of CFTS thin films

Cu₂FeSnS₄ (CFTS) thin films were deposited by spray pyrolysis method on glass substrate. The CFTS precursor solution was prepared by mixing CuCl₂. 2H₂O (0.1 M), FeCl₃. 6H₂O (0.05 M) and SnCl₄·5H₂O (0.05 M) in 50 ml double-distilled water. Tin (IV) chloride react with water to produce tin (IV) hydroxide and hydrogen chloride (hydrolysis of SnCl₄) as follows:SnCl₄ + 4H₂O ⇄ Sn(OH)₄ + 4HCl

Therefore, In order to enhance the solubility of tin chloride, a few drops of hydrochloric acid (typically of the same or

Structural characterization

Fig. 1 presents the X-ray diffraction patterns of CFTS films deposited at different substrate temperatures (250, 290, 330 and 370 °C). All thin films are polycrystalline irrespective of substrate temperature. The data analysis show the single stannite structure of Cu₂FeSnS₄ (JCPDS No. 44-1476) in the tetragonal space group I-42m, with the major diffraction peaks (112), (200), (220), and (116) in all the studied samples [10], [11], [12]. Also, with increasing the substrate temperature, the

Conclusions

Quaternary CFTS films were deposited on heated glass at different substrate temperatures

(250–370 °C) by spray pyrolysis technique without sulfurization under a non-vacuum condition. The effects of substrate temperature on the structure, morphology, composition, optical, electrical and photoconductivity properties of CFTS thin films were investigated. XRD results reveal that the CFTS formation starts at a low temperature as 250 °C and continues till 370 °C. At low deposition temperatures the CFTS

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Preparation and characterization of Cu2FeSnS4 quaternary semiconductor thin films via the spray pyrolysis technique for photovoltaic applications

Highlights

Abstract

Introduction

Section snippets

Synthesis of CFTS thin films

Structural characterization

Conclusions

Sol. Energy Mater. Sol. Cells

Mater

Mater. Lett.

Mater. Sci. Semicon. Process.

Thin Solid Films

Ceram. Int.

Thin Solid Films

Sol. Energy Mater. Sol. Cells

Prog. Photovolt.

Energy

Thin Film Processes

Thin Solid Films

Preparation and characterization of Cu₂FeSnS₄ quaternary semiconductor thin films via the spray pyrolysis technique for photovoltaic applications