Optical And Structural Properties Of Copper Aluminum Diselenide (CuAlSe2) Compound Thin Films

Optical And Structural Properties Of Copper Aluminum Diselenide (CuAlSe2) Compound Thin Films

Abstract

A low cost chemical bath deposition technique has been used for the preparation of Copper aluminum diselenide (CuAlSe2) thin films onto commercial microscope glass substrates. The values of deposition parameters were varied such as temperature (50-70oC), deposition time (12 – 60hrs), volume of complexiing agent (1-9ml) and bath pH (8.35 – 10.10) to obtain good quality thin films. The optical, structural and morphological properties of thin films were studied by Jenway Software 6405 UV – VIS Spectrophotometer, X-ray minidiffractometer MD – 10 and Scanning Electron Microscopy (SEM) studies respectively.

The optical property revealed that CuAlSe2 films have energy band gaps range value at room temperature and elevated temperature as 2.22 – 2.58eV and 2.00 – 2.14eV respectively. The X-ray diffraction study showed that the CuAlSe2 films were polycrystalline in nature with the preferential orientation along the (112) plane. The Scanning Electron Microscopy results indicated that the films were smooth, uniform and the substrate surface was covered completely at these experimental conditions.

Chapter One

1.0 Introduction

Copper selenide (CuSe) belongs to I–VI compound semiconductor materials. Copper (I) selenide exists in the cubic, orthorhombic, tetragonal or monoclinic forms. Copper selenide heterojunction solar cells are cost effective and high-efficiency devices used in the solar energy conversions. CuSe is also used in the fabrication of photovoltaic devices such as window material, super ionic conductor, electro-optical devices, optical filter, thermo electric converter and photo electrochemical cell. CuSe alloys have been one of the most studied in recent years, with stoichiometric (α-Cu2Se, Cu3Se2, CuSe, and Cu2Se) and non-stoichiometric (Cu2-xSe) compositions exhibiting a continuous change of physical properties. In addition, various crystalline phases have been reported with orthorhombic, cubic, hexagonal, and tetragonal structure, depending on the stoichiometry and the growth methods. These features make the electrical and optical properties interesting for applications in solar cells, super ionic conductor, optical filters and lasers. The CuSe semiconductor could be a direct gap of 2.2 eV or 1.4 eV indirect.
Thin and continuous films with desired electrical and optical properties are required for the preparation of photoelectrochemical solar cells. It is easier said than done to obtain continuous and single phase (CuAlSe2) film with the above mentioned properties. Electrodeposition is one of the suitable methods to prepare thin and continuous semiconducting films. This technique provides numerous advantages such as low temperature processing, low cost of synthesis, no need of vacuum facility, no contamination to the surrounding. It is simply possible to control film thickness and morphology by readily adjusting the electrical parameters as well as the composition of the electrolytic solution.The (CuAlSe2) thin films prepared by thermal evaporation and their structural, electrical and optical properties have been studied. Preparation of (CuAlSe2) thin films by vacuum evaporation technique and its annealing effect on structural, morphological, compositional and optical properties have been investigated.Growth of (CuAlSe2) thin films using thermal evaporation method and their properties have been investigated using structural, optical absorption, and Raman spectroscopic techniques. The grown (CuAlSe2) thin films and their properties have been investigated using X-ray diffraction, scanning electron microscopy and optical absorption techniques. To the best of our knowledge, no such detailed investigation is available for studying the properties of (CuAlSe2) thin films which have been obtained using electrodeposition technique.

Copper Aluminum Diselenide has such electrical and optical properties that are appropriate for a number of photovoltaic applications. Copper Aluminum Diselenide induces much interest since it has been broadly used as solar cell applications. (CuAlSe2) thin films can be deposited by different techniques such as physical vapour deposition, pulse laser evaporation, electro deposition, spray pyrolysis, metal organic vapour phase epitaxy (MOVPE)/metal organic chemical vapour deposition (MOCVD), screen printing, successive ionic layer adsorption reaction (SILAR), RF sputtering, and chemical bath deposition (CBD). Thin film heterojunctions solar cells play asignificant role as low cost, large area and high efficiency devices in solar energy conversion. In the present paper is discussed how the (CuAlSe2) thin films can be deposited on the glass substrates by CBD method and how they can be characterized by X-ray diffraction, scanning electron microscopy (SEM), UV analysis, dielectric studies and photoconductivity measurement.

1.1 Objectives

To study the optical and structural properties of CopperAluminum Diselenide (Cualse2) compound thin films.

1.2 Scope of Study

The scope of this study is within the circumference of understanding the structural and optical properties of Copper Aluminum Diselenide compound thin films

1.3 Research Questions

1. What are the optical properties of Copper Aluminum Diselenide?
2. What are the structural properties of Copper Aluminum Diselenide?

1.4 Limitations

Issues encountered while carrying out this project were in the acquisition of materials, equipment and apparatus used to execute the project.

Chapter Five

5.0 Conclusion

The films of CuAlSe2 were successfully deposited using chemical deposition technique onto commercial microscope glass substrates at variation of deposition temperature. The optical properties show that films could be useful in photovoltaic solar cell applications and thermal window coatings. The influence of deposition temperature in this research shows that: absorbance and optical conductivity increase as the deposition temperature decrease, but increase in reflectance and film thicknesses bring about increase in bath temperature. The energy band gap is in the range of 2.00 to 2.14 eV which shows that it is potentially useful for blue light-emitting diodes. The band gap energy decreases as the deposition temperature increases. It does agree with the fact that increase in temperature brings about decrease in difference between the conduction band minimum and valence band maximum which is called the energy band gap.

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