Spray pyrolytic deposition of polycrystalline Cu2S thin films

doi:10.1016/j.matchemphys.2011.10.015

Materials Chemistry and Physics

Volume 131, Issues 1–2, 15 December 2011, Pages 525-528

https://doi.org/10.1016/j.matchemphys.2011.10.015 Get rights and content

Abstract

Polycrystalline copper sulfide (Cu₂S) thin films were deposited by spray pyrolysis using aqueous solutions of copper nitrate and thiourea without any complexing agent at substrate (deposition) temperature of ∼200 °C. The films were deposited onto glass and ITO-coated glass substrates. The deposited films were observed to be blackish brown in color, well adherent to the substrate, pin-hole free and uniform. The structural, surface morphological and optical properties of the films were carried out by means of X-ray diffraction, scanning electron microscopy and optical absorbance measurement techniques. XRD analysis showed that deposited films are chemically close to chalcocite, Cu₂S. The optical band gap was calculated to be 1.5 eV.

Highlights

► Synthesis of polycrystalline Cu₂S films with band gap of 1.5 eV which is truly useful for solar cell applications. ► Deposition has been carried out without any complexing agent. ► Films are compact.

Introduction

Copper sulfide represents an interesting class of p-type semi-conducting materials which are attractive for large scale applications because of the easy availability of the starting materials. Copper sulfide is used in a variety of scientific and technological applications, such as photovoltaic cells, because it can exhibit tunable semiconductive or approximate metallic behavior depending on the stoichiometry of the mineral phase [1]. At least five stable phases, such as chalcocite (Cu₂S), djurleite (Cu_1.95S), digenite (Cu_1.8S), anilite (Cu_1.75S) and covellite (CuS) are known to exit at room temperature [2]. For more than 3 decades, much of interest in copper sulfide has been due to their use in CdS/Cu₂S hetero-junction solar cells [3], [4]. Copper sulfide nanoparticles have demonstrated a third-order optical non-linearity when trapped in the glass/polymer matrix [5], [6]. Composites of copper sulfides with ZnS and CdS have been viewed as promising luminescent materials [7], [8]. An important short coming of this material is the spontaneous disproportion from initial copper (I) to copper (II) phase [9], [10]. Copper sulfide is an interesting material for its metal-like electrical conductivity, chemical sensing capability and ideal characteristics for solar energy absorption [11], [12]. Copper sulfide is a good prospective optoelectronic material, which is often used for ammonia gas sensing at room temperature [13], [14]. The gas sensitive parameters have been found to dependent upon the chemical composition and the morphology of the Cu_xS material [15], [16]. The spray pyrolysis method has been used to deposit copper sulfide, Cu_xS (x = 1–2) films because it is relatively cheap and simple [17], [20]. Nascu et al. [18] reported deposition of CuS using CuCl₂, CS(NH₂)₂ and pyrydinium bromide (cationic surfactant) and Wang et al. [19] reported deposition of Cu_xS (x = 1, 2) thin films using asynchronous-pulse ultrasonic spray pyrolysis technique without any complexing agent. The deposited Cu₂S films were a mixture of amorphous and polycrystalline.

In the present investigation, attempt has been made to deposit polycrystalline Cu₂S films, which can find a potential application in photovoltaic, by spray pyrolysis technique. The films were deposited onto glass and ITO-coated glass substrates at substrate (deposition) temperature of ∼200 °C. These films were characterized for their structural, surface morphological and optical properties.

Section snippets

Experimental

Copper sulfide thin films were deposited using a mixture of aqueous solutions of 0.2 M copper (II) nitrate tri-hydrate, (Cu(NO₃)₂·3H₂O) and 0.1 M thiourea, CS(NH₂)₂. Copper nitrate was purchased from STREM, USA and thiourea was purchased from Sigma–Aldrich, USA. The chemicals are used as received without any further purification. The effective area of glass substrate was 75 mm × 25 mm. The substrate temperature was ∼200 °C (heater plate temperature ∼400 °C). The nozzle to substrate distance and the

Film formation reaction

Thermogravimetric (TG) curve in Ar atmosphere for copper nitrate and thiourea sample are as shown in Fig. 1, Fig. 2, respectively. TG analysis was performed in temperature range of 25–600 °C for copper nitrate and 25–1000 °C for thiourea sample. Copper nitrate and thiourea TG curve indicates weight losses at different temperatures. In case of copper nitrate the first rapid weight loss up to 200 °C attributed to the removal of water molecules as shown in Fig. 1. The mass loss determined by TG curve

Conclusions

The spray pyrolysis technique was successfully used to deposit copper sulfide thin films from copper nitrate and thiourea at relatively low temperature without any complexing agent. The films were characterized by XRD, SEM and optical spectroscopy. XRD studies indicated that the films were polycrystalline Cu₂S. SEM micrographs showed that substrates are well covered. From optical studies, direct band gap was found to be 1.5 eV.

Acknowledgements

This research was performed for the Hydrogen Energy R and D Centre, one of the 21st Century Frontier R and D program, funded by the Ministry of Science and Technology of Korea.

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Spray pyrolytic deposition of polycrystalline Cu2S thin films

Abstract

Highlights

Introduction

Section snippets

Experimental

Film formation reaction

Conclusions

Acknowledgements

J. Solid state Chem.

Solid State Commun.

J. Cryst. Growth

J. Solid State Chem.

Solid State Commun.

Sens. Actuators B

J. Eur. Ceram. Soc.

Mater. Lett.

Mater. Sci. Eng. B

Appl. Surf. Sci.

Solar Energy Mater. Solar Cells

Langmuir

Semicond. Sci. Technol.

Spray pyrolytic deposition of polycrystalline Cu₂S thin films