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Composition and Morphology of Copper Bismuth Selenide Layer on Glass Prepared by Chemical Conversion Technique

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Composition and Morphology of Copper Bismuth Selenide Layer on Glass Prepared by Chemical Conversion Technique CHEMIJA. 2019. Vol. 30. No. 1. P. 33–40 © Lietuvos mokslų akademija, 2019 Composition and morphology of copper bismuth selenide layer on glass prepared by chemical conversion technique Viktorija Osipovaitė, A copper bismuth selenide layer prepared by the chemical conversion of a copper selenide layer on glass has been studied. SEM images display layers with a non- Ingrida Ancutienė* homogeneous morphology. The copper selenide layer was non-uniform and con- sisted of dendrites and particulated agglomerates. The surface of the chemically Department of Physical and converted layer was denser and smoother with closely spaced spherical grains. Inorganic Chemistry, The EDX results reveal that the converted samples are rich in copper and poor in Kaunas University of Technology, bismuth. The phases of copper selenides in the obtained layer and copper bismuth Radvilėnų Rd. 19, selenide and hexagonal selenium in the annealed converted layer were detected 50254 Kaunas, Lithuania using the XRD analysis. Copper selenide peaks are most dominant with the hex- agonal klockmannite phase. Keywords: selenopolythionates, copper selenide, copper bismuth selenide, SEM- EDX, XRD INTRODUCTION tion for use in photovoltaics, thermoelectric de- vices, photoconductive materials, and topological Due to extensive applications and future pros- insulators [5–7]. Bi2Se3 is one of the widely stud- pects, semiconducting chalcogenide films have re- ied material because of its suitable optical prop- ceived much attention in recent years. Thin films erties. Bismuth selenide is a narrow direct band play a crucial role in the present day science and gap semiconductor (Eg 0.3 eV) and its tunable technology due to their wide use in a large num- band gap is useful for solar cell applications [8, 9]. ber of active and passive devices [1]. Metal chal- ∼ Bi2Se3 has attracted considerable attention due to cogenide thin layers are of particular interest for its characteristic anisotropic layered structure as the fabrication of large area photodiode arrays, well as important applications in the field of opti- solar selective coatings, solar cells, photoconduc- cal recording systems and stain gauges [9, 10]. For tors, sensors, and so on [2]. Binary, ternary and bismuth based compound CuBiSe2 a direct band quaternary chalcogenide layers are suitable for gap is in the range 1.1–1.5 eV, and it has been sug- a wide range of solar cell application [3, 4]. gested as photovoltaic absorber material [11, 12]. Bismuth chalcogenides (Bi2X3, X = S, Se, Te) are This ternary semiconductor contains elements semiconductor compounds that have gained atten- like Cu and Bi that are earth-abundant and non- * Corresponding author. Email: [email protected] toxic [3]. 34 Viktorija Osipovaitė, Ingrida Ancutienė The synthesis of various metal selenides lay- copper salts consisting of 0.34 mol/L Cu(II) and ers has been realized by many methods, such 0.06 mol/L Cu(I) salt [19]. The process of layer as chemical bath deposition [13–15], succes- formation was repeated three times in order to sive ionic layer adsorption and reaction [13, 16, achieve the suitable thickness. Later the sub- 17], electrodeposition [12, 18], evaporation [10], strates were rinsed with distilled water and sub- etc. Mostly used approaches to synthesize metal merged in a 0.1 mol/L Bi(NO3)3 solution with selenides are chemical bath deposition (CBD) triethanolamine (pH ≈ 9) for 20 min at 60°C; and successive ionic layer adsorption and reac- the samples were rinsed in distilled water again tion (SILAR) methods [2]. These methods are and dried over CaCl2. Finally, the samples were well known and commonly used for the prepa- annealed for 24 h in the inert nitrogen atmos- ration of thin films because of their low tem- phere at 100°C. perature requirement, low cost, suitability for For the characterization of the obtained layers large-scale deposition areas and ability to de- the XRD analysis and SEM-EDX measurements posit films on different types of substrates. How- were recorded. The XRD studies on a D8 Advance ever, using the CBD method a precipitate forms diffractometer (Bruker AXS, Germany) operating in the bulk of solution, this wastage of materi- at 40 k tube voltage and 40 mA tube current were als is avoided in the SILAR method when thin performed. Diffraction patterns were recorded in films are obtained by immersing a substrate Bragg–Brentano geometry, using a fast counting into separately placed cationic and anionic pre- 1-dimensional detector Bruker LynxEye based cursors and rinsing with water between each on silicon strip technology. The X-ray beam was immersion [13]. filtered with a Ni 0.02 mm filter to suppress Cu-k In this paper we report on the formation alfa β-radiation and the specimens were scanned of copper bismuth selenides layers on glass by over the range 2θ = 3–70° at a scanning speed the SILAR method. As the precursor of selenium of 6° 1/min using a coupled two theta/theta scan we used solutions of selenopolythionate acids, type. The diffractometer is supplied together H2SenS2O6. The layers formed were characterized with the software package DIFFRAC.SUITE. using scanning electron microscopy coupled with X-ray diffractograms of the deposited layers were energy dispersive X-ray spectroscopy (SEM-EDX) processed using the software packages Search and X-ray diffraction (XRD) analysis in order to Match, ConvX, Xfit and Microsoft Office Excel. determine the morphology, chemical and phase In order to study the morphology of the samples composition of the obtained layers. and the elemental composition of the obtained layers a scanning electron microscope Raith EXPERIMENTAL e-Line (Raith, Germany) equipped with an en- ergy dispersive spectrometer Quantax 400 with Layers of copper and copper bismuth selenides a detector XFlash 3001 (Bruker AXS, Germany) on soda lime glass substrates with one side was used. sandblasted were obtained. The substrates of All reagents used in the experiments were 10 × 10 × 1 mm were first cleaned with a liquid chemically and analytically pure commercial soap and washed with distilled water, then they reagents. Selenous acid, H2SeO3 (99.999% trace were cleaned ultrasonically in an acetone bath metals basis from Sigma-Aldrich), sodium hy- by using a Sonoswiss SW 3 H cleaner for 10 min drosulfite, NaHSO3 (≥99% from Sigma-Al- at 40°C using the sweep mode. The substrates drich), crystalline copper sulphate pentahydrate, were dried in air and used for layer deposition. CuSO4 · 5H2O (crystals and lumps, 99.999% The selenium layer was formed by submerging trace metals basis, from Sigma-Aldrich), hyd- the glass substrate into a 0.4 mol/L H2SeO3 and roquinone, C6H4(OH)2 (flakes, ≥99% Reagent- 1 mol/L NaHSO3 1:1 mixture for 3 h at 60°C. Plus® from Sigma-Aldrich), bismuth(III) nitrate Then, the sample was rinsed in distilled water pentahydrate, Bi(NO3)3 · 5H2O (reagent grade, and placed in a solution of 0.4 mol/L CuSO4 with 98% from Sigma-Aldrich), triethanolamine, an addition of 1% hydroquinone for 10 min at (HOCH2CH2)3N (≥98% from Sigma-Aldrich) 60°C. It is a mixture of univalent and divalent were used for the experiments. 35 Viktorija Osipovaitė, Ingrida Ancutienė RESULTS AND DISCUSSION to be non-uniform with a dendritic structure. It is clearly seen that this layer forms after the aggrega- It is known [20] that components of a selenous tion of irregular-shaped particles. The addition of acid and sodium hydrosulfite mixture react with bismuth ions drastically changed the microstruc- each other and diseleniumtetrathionate acid in ture of the layer (Fig. 2). The surface of the con- a solution is formed: verted layer is denser, smoother and covered by closely spaced spherical shaped grains. The size of 2H2SeO3 + 5NaHSO3 → H2Se2S2O6 + spherical grains was 1–8 μm. EDX spectroscopy was used to determine (1) + 2Na2SO4 + NaHSO4 + 3H2O. the elemental composition of the formed and con- verted layers. The EDX spectrum of the obtained By heating diseleniumtetrathionate decom- copper selenide layer shows the presence of Cu, poses and releases elemental selenium, which is Se and Si peaks (Fig. 1). One of selenium peaks deposited on a glass substrate: is especially intense. This indicates that the layer contains an excess of elemental selenium. The ex- 2– 2– Se2S2O6 → Se + SeS2O6 . (2) istence of silicon is believed to have appeared from a glass substrate. The EDX results confirm Seleniumtrithionate formed is not stable and the presence of bismuth, selenium and copper in decomposes: the converted sample (Fig. 2). A comparison of the EDX spectroscopy data of those layers shows 2– 2– SeS2O6 → Se + SO4 + SO2. (3) the reduction of copper and selenium in the con- verted layer (Table). That means that copper ions Copper selenides form during the heteroge- are released from the copper selenide layer dur- neous oxidation-reduction reaction between el- ing reaction with bismuth (III) ions, as shown in emental selenium on glass and Cu+ in the copper Eq. (5), and the amount of copper in the converted salt solution: layer decreased. The results indicate that the con- verted layer is rich in copper (25.01 at.%) and + 2+ % Se + 2xCu → CuxSe + xCu . (4) poor in bismuth (5.25 at. ). This could be due to the fact that a 3-cycle copper selenide layer was In order to prepare bismuth selenide layers, used for chemical conversion by a bismuth salt the CuxSe layers on glass are chemically converted solution. by a bismuth nitrate solution. Such a chemical The phase composition of a layer was estab- process allows an exchange of copper ions by bis- lished by comparing its X-ray diffraction pat- muth ions and may be described by tern with those of known minerals, the area of 2Θ ≥ 20.0° was investigated in more detail. 3+ 3CuSe + 3Cu2Se + 4Bi → The results of the phase analysis of the samples (5) with a formed three-cycle copper selenide layer 2+ + 2Bi2Se3 + 3Cu + 6Cu .
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