Tuning the structural, optical and electrical properties of AgInSe₂ thin films prepared by sequentially deposited silver and indium nano-films under vacuum

Abstract

This paper reports the successful preparation of AgInSe₂ thin films by thermal evaporation of Ag and In elements followed by a heat treatment in selenide atmosphere at various temperatures. X-ray diffraction analysis shows that the annealed film at T = 400 °C is well crystallised in AgInSe₂ chalcopyrite phase with crystallinity preferentially oriented towards (112) direction. Moreover, the annealing treatment has effective role in the enhancement of the surface morphology by means of atomic force microscopy observations especially for film heated at 400 °C. The optical transmittance and reflectance measurement reveals that the band gap energy Eg is 1.35 eV. The X-ray photoelectron spectrometry (XPS) spectra show that the binding energies of the elements are in good agreement with bonds of AgInSe₂. On the other hand, the electrical conductivity of AgInSe₂ film prepared in the present experiment has been performed in 100–300 K domain showing a semiconductor behavior of this material. Also, the carrier concentration and carrier mobility have been measured by Hall measurements. This film can found interest for sensitivity applications including photocatalysis, gas and biosensors.

Introduction

Solar cell technologies using I-III-VI₂ compounds have been extensively reported because of their interesting electrical and optical properties [1]. AgInSe₂ is a possible candidate because of its large band gap energy value which is ranging from 1.37 to 1.45 eV. Some of I–III–VI₂ ternary compounds belonging to chalcopyrite structure, analogues to II–VI compounds [2] are closely related to zinc blend structure. From this ternary group, AgInSe₂ with a space group of

I $\overline{4}$ 2d is a ternary similar to CdSe. This material has been used in nonlinear laser devices [3], and exhibits possible photovoltaic performance in solar cell disposals because its optical band gap lies between 0.8 and 2.0 eV and it can be grown either n or p-type [4].

This ternary material was first prepared by Hahn and all. in 1953 [5] from the original binary compounds. It was also synthesized directly from the elements in sealed evacuates silica tubes [6,7]. In the same line, thin films of AgInSe₂ have been prepared by various methods such as: the flash evaporation technique [8,9], co-evaporation [10,11], microwave [12], pulse laser vaporization [13], electrodeposited [14], and RF magnetron sputtering [15], and thermal evaporation [16,17].

Recently, we are witnessing an increase in the synthesis of AgInSe₂ in various nanoforms including quantum dots. Indeed, it is reported that AgInSe₂ /CdS/ZnS core/shell/shell quantum dot sensitized solar cells (QDSS) achieved a relatively high conversion efficiency exceeding 6% [18]. In the same line, AgInSe₂-quantum-dot-sensitized solar cell exhibited excellent performance with TiCl₄ treatment and an excellent power conversion efficiency of 5.69% was obtained under 100 mW cm⁻² illumination [19].

The purpose of this work is to use a simple and low temperature preparation technique to deposit AgInSe₂ thin films. This ternary material achieved by selenization of a metallic precursor constituted of sequentially deposited of silver and indium layers In/Ag/In…Ag/In/Ag. First, the structural properties of AgInSe₂ were characterized by X-Ray Diffraction (XRD), by Atomic force microscopy (AFM). Second, their optical and electrical properties have been studied. Finally, a specific emphasis is put on the XPS investigation on prepared films. To date, this procedure to prepare this ternary compound has not been used.