Study of Nickel oxide thin films deposited by spray pyrolysis, solar cells applications
BAHI AZZOUOUM Ahmed1, Benyahia ahmed 2, Bouhmidi Mohamed3
1 University of Science and Technology of Oran Mohamed Boudiaf (USTO-MB),3Laboratory Micro and Nanophysics (LaMiN), National Polytechnic School of Oran (ENP-Oran), BP 1523 El Mnaouer, Oran 31000, Algeria,
bahiahmed12@gmail.com
Abstract— Nickel oxide (NiO) thin films were deposited on glass substrates by chemical spray pyrolysis technique. A high quality crystal was obtained after annealing at 500 K. The structural properties of the films have been studied by the X-ray diffraction (XRD). It has been shown that thin films in the NiO crystallized structure is attained after the deposition. Whatever the precursor molarity, the grain size is about 28-62 nm. The crystallites are preferentially oriented in the directions (111) at 0.2M and (200) at 0.3M.
Keywords—Thin film; NiO; spray pyrolyse;
structural properties; solar cells; X-ray diffraction.
I. INTRODUCTION
Research and development on thin films has led to the conclusion that different classes of materials are of particular interest for different applications [1]. The first thin film of a transparent conductive oxide (TCO) of the p type is that of nickel oxide [2]. The NiO is a semiconductor having a face centered cubic structure [3].
Nickel oxide is of particular interest because the material has in recent a variety of applications in electronic devices, energy efficient smart windows, automobile mirrors and heterojunction solar cells [1].
II. EXPERIMENTAL PARTY II.1 ELABORATION OF THIN FILMS
The aim of our work is the development and characterization of nickel oxide thin films deposited by the technique of spray pyrolysis on glass substrates.
This method is simple to implement, low cost of development and it allows good control of deposition conditions (substrate temperature, concentration of the initial solution ...) [4-5].
The main experimental devices, fig.1, are constructed from simple devices:
A sprayer (atomizer) in the form of plastic bottle.
A substrate heater: consists of a heating plate.
A thermocouple: type GTH 1160.
Fig.1. Experimental devices of spray pyrolysis.
A. Preparation of substrates
The development of the thin film of NiO is carried on glass substrates, the choice of glass as was done for the optical and electrical characteristics of the substrate and for economic reasons. The substrates were glass slides in the form of rectangle of size (25 × 10 × 1) mm cut by an alumina rod.
The substrate cleaning is very important for obtaining films having a good adhesion to the substrate, a uniformity (constant thickness) and good structural and morphological properties. That is to say, elimination of impurities on the substrate, because they can prevent or inhibit the crystal growth during the deposition phase.
That is why we carry out the following steps before each deposition:Cleaning with Betadine (medical soap) to remove the last traces of dirt and grease hanging on surfaces.
Rinsing with distilled water.
Soaking for 15 minutes in acetone in a beaker at room temperature for degreasing.
Cleaning with distilled water for 10 minutes and drying in air.
B. Preparation of chemical solutions
The preparation of solution consists to dissolving the nickel chloride (NiCl2. 6H2O) in powder form in deionized water as the solvent.
C. Method of Spray
After preparation of the substrates, are placed over a resistor. These substrates are heated progressively until the selected temperature (350°C). When the heating is carried, very fine droplets are sprayed onto the heated substrates which causes, by pyrolysis, the activation of the chemical reaction between the compounds, the dissolving evaporates due to the reaction of the two compounds forming the thin film.
The sputtering is made according to cycles of 15s followed by pause of 30s to avoid the decrease in the substrate temperature. Finally the deposition process, the heating was stopped and the substrates were allowed to cool until the room temperature, to avoid thermal shocks that could break the glasses, then recovering our samples.
TABLE 1
The parameters used to deposit NiO thin films.
Substrate temperature 350 °C
Concentrations solutions 0.2 M 0.3 M
Nozzle height 30 cm
Number of cycles 08 cycles: deposition of 15s /pause of 30s Solution of spray
Nickel chloride [𝑁𝑖𝐶𝑙2. 6𝐻2𝑂] dissolving
in deionized water.
D. The annealing of NiO samples
After the deposition, the NiO thin films are annealed in an oven for 2 hours at 500 °C. This step can improve the crystallization of the films and the thermally stabilize.
II.2 CHARACTERIZATION OF NiO BY THE X-RAY DIFFRACTION
The identification of materials requires characterization means; we cite in this work X-ray diffraction technique that we used to characterize our thin films of NiO.
This method permits to determine the structure, crystallographic growth direction of the layers, measure the lattice parameters and the size of crystalline. To characterize our samples we used a diffractometer D8 ADVANCE Bruker type. The data has been converted to copper radiation (λ=1.54Å) by the X'PERT PLUS01 program.
III. RESULTS AND DISCUSSION With the aid of result diffractometer we draws the curves of intensity as a function of 2θ.
A. The NiO thin films before the annealing
Fig .2. XRD diagram of: NiO thin film elaborated at :
(a) 0.2M. (c) 0.3M.
We note that whatever the concentration of the solution, there are the presence of low intensity diffraction peaks belonging to a different phase of the nickel oxide, and therefore it has not been a preferred orientation.
B. The NiO thin films after the annealing
1. The films elaborated at 0.2M
Fig .3. XRD diagram of NiO thin films elaborated at 0.2M after annealing at 500 °C.
2. The films elaborated at 0.3M
Fig .4. XRD diagram of NiO thin films elaborated at 0.3M after annealing at 500 °C.
In the tables (II) and (III), we present the crystal parameters of our thin films after annealing such as interrérticulaires distances and corresponding hkl, the lattice parameters and the average grain size.
TABLE II
The crystalline parameter values of the NiO thin films obtained at 0.2M after annealing at 500 °C.
2θ (deg)
hkl I
(%) 𝐼0 (%)
𝑑ℎ𝑘𝑙 (Å)
𝑎𝑐𝑎𝑙𝑐𝑢𝑙𝑎𝑡𝑒𝑑 (Å)
FWHM (deg)
D (nm)
37.39 (111) 100 91 2.40 0.13
43.44 (200) 60 100 2.08 0.19 62
63.01 (220) 23.33 57 1.47 a=4.1621 0.31
75.57 (311) 6.66 16 1.25 0.46
79.58 (222) 3.33 13 1.20 0.56
TABLE III
The crystalline parameter values of the NiO thin films obtained at 0.3M after annealing at 500 °C.
2θ (deg)
hkl I
(%) 𝐼0 (%)
𝑑ℎ𝑘𝑙 (Å)
𝑎𝑐𝑎𝑙𝑐𝑢𝑙𝑎𝑡𝑒𝑑 (Å)
FWHM (deg)
D (nm)
37.38 (111) 73.32 91 2.40 0.27
43.45 (200) 100 100 2.08 0.31 28
63.02 (220) 29.99 57 1.47 a=4.1616 0.19
75.55 (311) 6.66 16 1.25 0.46
79.60 (222) 3.33 13 1.20 0.56
It has been shown that:
The XRD diagrams show that these films are polycrystalline nature.
The rays diffraction diagrams X show that the films are well crystallized after annealing for two hours at 500 ° C.
The confrontation of the data to the JCPDS card N°04- 0835 [6] has helped to conform the faces centered cubic structure with a lattice constant a = 4.1769 Å.
The calculated values of the lattice parameters are in good agreement with those theoretically calculated.
After annealing at 500 °C, the preferential grain orientation is along the axis (111) to the films developed at 0.2M while it is along the axis (200) to the films elaborated at 0.3M.
IV. CONCLUSION
We have studied nickel oxide thin films deposited by chemical spray pyrolysis technique.
We are interested to the structural characterization of films by X-ray diffraction.
The X-ray diffraction has allowed us to identify the structure rocksalt of NiO (face-centered cubic). After annealing at 500 ° C, the preferential grain orientation is along the axis (111) to the films elaborated at 0.2M while it is along the axis (200) for the films elaborated at 0.3M.
The experimental results suggest that the annealing temperature and the concentration of the solution used has a great influence on the structural properties of thin films of NiO.
REFERENCES
[1] A. Hakim et al,« Temperature effect on the electrical properties of undoped NiO thin films », Renewable Energy, 34 (2009) 2625–2629.
[2] Maevä LALANNE, doctoral thesis « Etude de phases delafossite Cu Fe1−XCrxO2 : vers de nouveaux TCO de type P », University of Toulouse, 2010.
[3] Asmae. BOUZOUBAA, doctoral thesis, «Modélisation atomistique des interactions entre les ions chlorures et la surface du nickel passivé», University of Pierre et Marie Curie - Paris VI, 2008.
[4] K.Omura, P.Veluchamy, M. Tsuji, T.Nisho, M.Murozono "
Pyrosol technique to deposit highly transparent, low-resistance SnO2:F thin films from dimethyltindichloride " Journal of the electrochemical society, 146(6), (1999) 2113.
[5] U.Schmatz, G.Delabouglise, M.Labeau, J.Garden " Electrical and microstructural studies of SnO2 ceramics obtained by tin sulfate pyrolysis " Journal of the Electrochemical Society, 141(11) (1994) p.3254.
[6] JCPDS (Joint Committee for Powder diffraction Standards) Data Cards. Swarthmore, PA, 04–0835, 1997.
