Electrochemical impedance analysis of spray deposited CZTS thin film: Effect of Se introduction

doi:10.1016/j.optmat.2016.06.011

Optical Materials

Volume 58, August 2016, Pages 418-425

https://doi.org/10.1016/j.optmat.2016.06.011 Get rights and content

Highlights

•
The effect of Se introduction in the CZTS film was investigated.
•
Electrochemical studies of CZTSSe films were examined using impedance technique.
•
The electrochemical (photo) studies were performed.

Abstract

The present work deals with electrochemical impedance analysis of spray deposited Cu₂ZnSnS₄ (CZTS) thin films grown on fluorine doped tin oxide (FTO) substrates and effect of post Se introduction. The CZTS thin films are characterized using X-ray diffraction (XRD), X-Ray photo spectroscopy (XPS), field emission scanning electron microscopy (FE-SEM) and UV–Vis spectroscopy techniques. The electrochemical measurements are carried out using impedance analysis spectroscopy. The strong peak in XRD pattern along (112) plane confirms the Kestrite crystal structure of CZTS film. The FE-SEM analysis reveals that nanoflakes contain crack-free surface microstructure changes with post Se introucation. The optical study reveals that absorption increases with Se dipping time and observed lower band gap of 1.31 eV. Introduction of Se in CZTS film results an improvement in the grain size and surface morphology which leads to increased electrical conductivity of CZTS film.

Introduction

An increasing demands of electrical energy storage and conversion cost need to have an intensive research on clean, ecofriendly and sustainable substitute energy sources [1]. Thin film photovoltaic technology being used more popular than Si solar cell to share and expecting material of an increasing demands of energy. Contempt the better results of thin film technology, several materials have been employed in solar cell applications. However, expensive, toxicity, rarely availability these materials are has limited use in present form. The materials should fulfill the criteria of good absorber, low toxicity and inexpensive for use in thin film solar cell [2].

Many semiconductor materials such as metal oxides and metal chalcogenides have been used for solar cell applications. To obtain most effective renewable solar energy researchers have focused on Cu₂ZnSnS₄ (CZTS) solar cell. There have been many reports on enhancement of photovoltaic cell performance with selenium replacing or introducing. Introduction of selenium ions in CZTS material could accomplish by using excess Se ligand in a precursor solution or selenization using H₂Se or Se gaseous [3], [4]. It is supportive direction to the formation of Se-substituted partially or completely in the pure CZTS material [5]. CZTSSe material extends a high absorption coefficient (10⁴ cm⁻¹) with a tunable band gap (from 1.0 to 1.5 eV) that can favorably match the solar spectrum [6]. The CZTSSe thin films were prepared by Larramona et al. [7] from water–ethanol CZTS colloidal solution using spray pyrolysis method and estimated solar cell conversion efficiency of 8.6%. Erkan et al. [8] prepared CZTSSe films and studied the effects of KCN and NH₄OH etching on the performance of solar cell. Guo et al. [9] reported to enhance the performance of CZTSSe solar cell with Ge alloying. In order to improve the photoelectrochemical cell (PEC) performance of CZTS material, electrochemical properties such as solution and charge transfer resistance, phase angle, capacitance-frequency relation, and flat band potential are important.

In this work, electrochemical performance of CZTS thin films deposited by spray pyrolysis method and effect of Se introduction in CZTS are studied. The physico-chemical properties of CZTS films are investigated. Subsequently, the electrochemical analyse of CZTS film with Se introduction are carried out.

Section snippets

Experimental details

CZTS thin films were deposited onto fluorine doped tin oxide (FTO) glass substrates by computer based spray pyrolysis method using an aqueous acidic solution containing cupric acetate (0.025 M), zinc acetate (0.025 M), stannic chloride (0.025 M) and thiourea (0.2 M). The individual Cu, Zn, Sn and S precursor solutions were mixed in 2:1:1:4 ratios and sprayed through the nozzle on the pre-heated FTO glass substrate. The CZTS films were deposited at various substrate temperatures within the range

Reaction mechanism

For the formation of Cu₂ZnSnS₄ film by spray pyrolysis method, very fine droplets of precursor solution thermally decomposes after falling over the preheated FTO substrate surface. The films is formed by surface nucleation and the growth of the solid film takes place by coalescence of the large number of critical nuclei. The following reaction was proposed for the formation of CZTS [10], $2 Cu ({CH}_{3} COO) + Zn ({CH}_{3} {COO)}_{2} + {SnCl}_{4} + {8 H}_{2} O + 4 SC {({NH}_{2})}_{2} \overset{Δ 648 K}{\to} {Cu}_{2} {ZnSnS}_{4} + {4 CO}_{2} ↑ + {4 CH}_{3} COOH ↑ + {4 NH}_{4} Cl ↑ + {4 NH}_{3} ↑$

Finally, brownish

Photoelectrochemical (PEC) measurement

Fig. 5(A) shows current-voltage (J-V) characteristic of CZTSSe film electrode in dark (a′) and under illumination (a–d) with different Se dipping time periods (0, 10, 20 and 30 min). From the curves it is seen that, the cathodic photocurrent increases gradually with increase in negative potential indicating that CZTSSe thin films are p-type in nature [21]. The PEC parameters such as, open-circuit voltage (Voc), short-circuit current density (Isc), fill factor (FF) and power conversion

Conclusions

CZTSSe thin films have been successfully deposited on FTO glass substrate by spray pyrolysis method and post Se introduction by dipping in Se solution. The physico-chemical properties of CZTSSe thin films are investigated to verify the influence of selenium. X-ray diffraction patterns confirm the formation of CZTS phase. Field emission scanning electron microscopy analysis reveals that CZTSSe_20 min thin film has good crystallinity with spherical grain chains. The photoelectrochemical

Acknowledgement

Authors are grateful to the Department of Science and Technology, New Delhi, India for financial support through the project scheme no. SERB/F/3982/2015-16.

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Electrochemical impedance analysis of spray deposited CZTS thin film: Effect of Se introduction

Highlights

Abstract

Introduction

Section snippets

Experimental details

Reaction mechanism

Photoelectrochemical (PEC) measurement

Conclusions

Acknowledgement

Sol. Energy Mater. Sol. Cells

Vacuum

Curr. Appl. Phys.

Adv. Energy Mater

Sol. Energy Mater. Sol. Cells

Sol. Energy Mater. Sol. Cells

J. Anal. Appl. Pyrolysis

J. Anal. Appl. Pyrolysis

Appl. Surf. Sci.

Int. J. Electrochem. Sci.

Mater. Res. Bull.

Sol. Energy Mater. Sol. Cells

Electrochim. Acta

Mater. Sci. Semicond. Process

Int. J. Electrochem. Sci.

Int. J. Electrochem. Sci.

Materials interface engineering for solution-processed photovoltaics

Nature