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PRACTICAL PROBLEMS AND SOLUTIONS TO THE USE OF THEORETICAL LAWS IN THE SCIENCES OF THE 21ST CENTURY
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EFFECT OF COMPLEXING AGENT ON THE STRUCTURAL, OPTICAL AND ELECTRICAL PROPERTIES OF POLYCRYSTALLINE INDIUM SULFIDETHIN FILMS DEPOSITED BY CHEMICAL BATH
DEPOSITION
Ismoilov Temur1, Murodbek Melikuziev2 and Rustambek Melikuziev3 Turayev Baxodir4
1,3,4 University of Tashkent for applied sciences, Gavhar Str. 1, 100149 Tashkent, Uzbekistan 2 Tashkent University of Information Technologies named after Muhammad al-Khwarizmi, Amir TemurStr 108,
Tashkent 100202, Uzbekistan [email protected], [email protected] https://doi.org/10.5281/zenodo.13377613 Abstract: Indium sulfide (p-In2S3) thin films are synthesized by chemical bath deposition method using three different complexing agent volumes, triethanolamine (TEA) (0.30, 0.45, and 0.60 ml). The effect of complexing agent on the structural, morphological, optical and electrical properties of chemically deposited indium sulfide (p-In2S3) thin films have been investigated in this work. The characterization of the present films is carried out using X-ray diffraction, scanning electron microscopy, UV-vis spectroscopy and electrical measurements. The structure of the films is polycrystalline with a cubic phase of p-In2S3. Firstly, the band gap of the film decreases from 3.74 eV to 3.15 eV by adding 0.30 ml TEA. Then, it increases to 3.79 eV with increasing TEA. Nevertheless, previously, the refractive index of the films increases from 2.13 to 2.67 for the 0.30 mL TEA and then it decreases to the value of 2.11 with increasing TEA. Extinction coefficient, real and dielectric constant of the films are calculated using the absorption and transmittance spectra. Firstly, the electrical resistivity of the films decreases from 3.46 108 Q cm to 1.33 107 Q cm by adding 0.30 ml TEA. Then, it increases to the value of 2.16 109 Q cm with increasing TEA. Eventually, the more conductive film with worm-like morphology detected from the scanning electron microscopy is synthesized using 0.30 ml TEA. These results show that complexing agent has an important effect on the structural, morphological, optical and electrical properties of the deposited films.
Keywords: structural, morphological, optical and
microscopy is synthesized. 1 INTRODUCTION
In recent years, p-In2S3 thin films have been extensively studied as a window material in thin film solar cells due to its exceptional optical and electronic properties, non-toxicity, chemical stability, and low cost
[1]. Because of having hazard to the environment, cadmium sulfide (CdS) has been replaced by p-In2S3 layer in the copper- indium-gallium-diselenide (CIGS) heterojunction in or- der to improve the solar conversion
[2]. p-In2S3 is an n-type semiconductor that belongs to the III-VI group of compounds with an optical bandgap in the range of 2.00 eV-3.91 eV [3]. Because of its high photosensitivity and photoconductivity, this material has also attracted intense interest as a potential visible-light photocata- lyst [4]. Pomaska et al. [5] fabricated chalcopyrite-based solar cells using In2S3 thin layers. The p-In2S3 exist in three crystallographic modifications a, p and y. Cubic structure of p-In2S3 is a stable phase at room tempera- ture. Thin films of this material have been prepared by different methods such as spray ions layer gas reaction (ILGAR) [5], radio
cal, chemically, polycrystalline, decreases, electron
frequency (RF) magnetron sputter- ing [6], chemical spray pyrolysis [7], sol-gel [8] and chem of compounds such as dip coating [10], electrodeposi- tion [11], electrospinning process [12], thermal barrier coatings [13], mechanical alloy [14] and two-step chemical etching process [15].Among them, the CBD technique is a more attractive technology which is well suited for coating large surfaces, low temperature processing, simple and inexpensive. In this technique, the preparation parameters can be con- trolled easily such as precursor concentrations, bath tem- perature, pH, substrates and film thickness.
In this work, we report that p-In2S3 thin films are synthesized by CBD technique. The effects of complex-ing agent on the structural, morphological, optical, and electrical properties of the films are investigated. The structure properties of the samples have been characterized by X-ray diffraction (XRD) and scanning electron microscopy (SEM). Moreover, the optical parameters and electrical properties of deposited films are studied.
PRACTICAL PROBLEMS AND SOLUTIONS TO THE USE OF THEORETICAL LAWS IN THE SCIENCES OF THE 2IST CENTURY
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2 EXPERIMENTAL DETAILS
The P-In2S3 thin films are deposited onto microscopecal bath deposition (CBD) [9].
Moreover, there are also other techniques for producing nanocrystalline structure of the III-VI and I-VI group glass substrates (7.6 cm 2.6 cm 0.1 cm) at room tem-perature (30 °C) using CBD method. In the present work, 10 ml of 0.1 M indium chloride (InCl3, Aldrich, > 99.99% purity), 3.15 M TEA ((HOCH2CH2)3N) as a complexing agent, 20 ml of 0.2 M acetic acid (CH3COOH, Merck, 100% purity) and 20 ml of 0.4 M thioacetamide (TAA, CH3CSNH2, Merck, ACS. Reag.) have been used. By adding deionized water, the total volume of the solution is completed to 50 ml. The films are obtained from the acidic bath (pH = 3.88). Cleaned substrates are placed vertically to the bottom of the beakers and waited for 69 h. After deposition, the films are rinsed with deion- ized water to remove loosely adhered particles on the film surfaces and then dried in air. TEA volume has been changed as
Mi
2C ' ^l^bBHMÄIä
0
A-A f T
. - "
' ■. T 1
200 nmgU WiliilTi'il
0.30, 0.45, and 0.60 ml to see the effect of complexing agent on the physical properties of the de- posited films. Preparation conditions for deposited films are listed in Table I.ratio changes in the synthesized films in the range 0.42-0.79. This means that our films show a large amount of sulfur deficiency.
Table I: Preparation condition and EDS analysis [at%] of P-In2S3 thin films synthesized with various TEA volumes [ml]. pH=3.88, T = 30 °C, deposition time = 69 h.
TEA Thickness [nm] In S S/In
0.00 394 61.63 38.37 0.62
0.30 355 55.78 44.22 0.79
0.45 300 70.52 29.48 0.42
0.60 247 56.41 43.59 0.77
The XRD measurements are carried out on a Bruker AXS D8 X-ray diffractometer with Cu Ka (X = 0.15418 nm). Surface morphology of the films are taken on a EV040-LE0 SEM system and the composition ra-tio of In and S were obtained by energy dispersive X- ray spectroscopy (EDS). The room temperature opti- cal
absorption spectra in the wavelength range of 3001100 nm is recorded by using a Perkin Elmer Lambda 4S UV-vis spectrophotometer. Keithley 2400 current-voltage (I V) source measuring system using computer-controlled 2-point probe technique is performed to get electrical resistivity values of the synthesized films. The thicknesses of the films (t) are determined by gravimetric method using t = m/pA with a precision microbalance, where m is the mass of the film, A is the surface area of the deposited film and p is the bulk
density of cubic P-M2S3 (4.6 g cm-3) [16]. 3 Results and discussion
Figure 1 shows the SEM images of the films prepared with different TEA volumes. In Fig. 1a, we observe that the particles can be clearly distinguished with some clus- ters and the average grain size of the particles is mea- sured as 24 nm. Figure 1b shows worm-shaped structure with cracks which has different morphological features from the others. In Fig. 1c and d, as TEA volume in- creases from 0.45 ml to 0.60 ml, these "worms" become shorter, being converted into grains whose diameter is about 66 nm and 22 nm, respectively. As can be seen from these morphologies, the smooth and well defined grains are obtained for the film synthesized at 0.60 ml TEA.
The compositional analysis of the films is obtained by EDS attached to the SEM and listed in Table I. The average ratio for atomic percentage of S/In is 1.5. This.
Fig. 1: SEM micrographs of P-In2S3 thin films obtained at 100k magnifications synthesized with different TEA volumes: (a) 0.00 ml, (b) 0.30 ml, (c) 0.45 ml, and (d) 0.60 ml.
The structural analysis of the films is performed by means of XRD patterns. Figure 2 shows the XRD patterns of P-M2S3 thin films with different TEA volumes. As can be seen from these figures, the broad hump between 15° and 40° is due to amorphous nature of P-M2S3 thin films. When compared with the observed and standard 20 values, it is concluded that the formed compound is P-In2S3 with cubic structure (PDF no. 320456). XRD results are consistent with previous data by Zhao Yang Zhong et al. [3], in which M2S3 thin films were synthe- sized by thermal evaporation process.
PRACTICAL PROBLEMS AND SOLUTIONS TO THE USE OF THEORETICAL LAWS IN THE SCIENCES OF THE 2IST CENTURY
TASHKENT. 0-8 MAY 2024
10 20 30 40 50 60 70 10 20 30 40 50 60 70
PDF no: 32-0456
(C) PDF no. 32-0456
f Î
-r
JEl
m
m:
20 (Degrees)
2«(Dcgrec)
Fig. 2: SEM micrographs of P-In2S3 thin films obtained at 100k magnifications synthesized with different TEA volumes: (a) 0.00 ml, (b) 0.30 ml, (c) 0.45 ml, and (d) 0.60 ml.
The film thicknesses of chemically deposited P-In2S3 thin films are calculated by gravimetric method listed in
......ml 11 A (b)
nlllml. MA
1145ml IIA
— ««0 ml " A ^^
300 450 600 750 900 1050 Mrnn)
300 450 600 750 900 1050 Jt(nm)
Fig. 3: (a) Absorbance and (b) transmittance spectraof P-In2S3 thin films synthesized at different TEA volumes.
Table I. The absorbance and transmittance spectra of the films with different TEA volumes are shown in Fig. 3a and b, respectively.
Table II: Film thickness and optical parameters (X = 600 nm) of P-In2S3 thin films with various TEA values.
TEA (ml] Es[tV] a k el c2 p ¡M ilcm|
0.00 3.74 2.13 0,33 4,44 1.40 346
O.JO 3.15 2.6 7 0,72 6.62 3.S7 13,3
0,45 3,64 2,15 0,49 4.38 2.10 557
0.60 3,79 2.11 0,64 4.03 2.72 2160
The complex refractive indexes of the P-In2S3 thin films are described as follows where n is the real part and k is the imaginary part of complex refractive index and given by k = aX/4n. The reflectance R is described by the Fresnel formulae [18] If one solves Eq. (2) via elementary algebraic manipula- tion, the refractive index is obtained as below. The absorption coefficient a is determined from the transmittance T spectra using the relation I0exp(-at) where t is the thickness of the film, I and 2 I0 are the intensities of the transmitted and incident light, respectively. The optical band gap of the P-M2S3 films is calculated using the relation given by ahv = B (hv - Eg)n [17], where B is a constant and n = '/2 for allowed direct transition. A plot of (ahv)2 against
photon energy hv shows a straight line portion, and the interception point of this linear portion on the energy axis at which (ahv)2 is equal to zero gives the direct band gap of the material. The (ahv)2 plots of the films deposited at different TEA volumes are shown in Fig. 4. Firstly, the band gap of the film decreases from 3.74 eV to 3.15 eV with adding 0.30 ml TEA. Then, it increases to 3.79 eV with increasing TEA volume. The estimated band gap values are listed in Table II. These results are in good agreement with previous works related to In2S3thin films [3, 6, 7].
(a)
I [k rxi Mil. TEA
\ -:> '0 ni il -
\ :i ni 11
\ ' ■'/ ni. TL.'
O.OO ml. TEA >0.30 ml.. TEA -CMS iuL TEA >0.60 in
(b>
300 450 600 750 900 1050 300 450 600 750 900 1050
—0.00 ml. TEA —0.10 ml, TEA -0.45 ml. TEA -0.60ml. TEA
300 450 600 750 900 1050 X (nm)
300 450 600 750 900 1050 X (mri)
n2 ,
Fig. 4: Plot of (ahv) versus hv for P-In2S3 thin films synthesized at different TEA volumes.
The complex refractive indexes of the P-In2S3 thin films are described as follows: n = n (X) + ik(X), (1) where n is the real part and k is the imaginary part of The dependence of n on wavelength for the P-In2S3 thin films is shown in Fig. 5a. In the visible range of wave- length (X = 600 nm), the refractive index varies between 2.11 and 2.67 in Table II. These values are in good agreement with the previous report (2.5) [19] and higher than in Ref. [20] (1.6-1.84). The variation of extinction coef- ficient with wavelength of the present films is also seen in Fig. 5b. At wavelength of 600 nm, it changes between 0.33 and 0.72 and these values are higher than the re- ported value (0.01) [20].
The real (81) and imaginary (82) dielectric constants are given by 81 = n2 k2 and 82 = 2nk, respectively. Figure 5c and d shows the plots of 81 and 82, respectively. At X = 600 nm, it can be seen that 81 and 82 change between 4.03-6.62 and 1.403.87, respectively.
300 450 600 750 TOO 1050 '300 450 600 750 900 1050
300 450 600 750 900 1050 300 450 600 750 900 1050
J. (nm) X (Tim)
Fig. 5: The variation of (a) refractive index, (b) extinction coefficient, (c) real and (d) imaginary dielectric constant for the P-In2S3 thin films synthesized at differ- ent TEA volumes.
The resistivities p of the films as a function of different TEA volumes are listed in Table II. A definite effect of the TEA on the electrical transport of the P-In2S3 thin films is observed. Initially, using 0.30 ml TEA causes a decrease from 3.46 108 Q cm to 1.33 107 Q cm in the resistivity of the films, but then a further in- crease in the pH leads to less conductive films with higher resistivities increasing from 1.33 107 Q cm to 2.16 109 Q cm. Eventually, the film deposited at 0.30 ml TEA becomes two orders of magnitude more conductive than the others. Resistivity values are consistent with re- ported data [17, 21, 22]. One possibility that might affect the resistivity is the morphology change in the films. As shown in the SEM images, the film with worm-shaped structure is synthesized using 0.30 ml TEA and it has different morphology than the others. 4 Conclusion
In summary, the thin films of P-M2S3 are synthesized onto microscope glass substrates with three differ- ent TEA volumes using CBD technique. The effect of complexing agent (TEA) on the structural optical and electrical properties of present films is investigated. X- ray diffraction pattern of the deposited films shows the formation of polycrystalline P-M2S3 thin films with cu- bic structure. When adding 0.30 ml TEA, the optical band gap of the films decreases from 3.74 eV to 3.15 eV. Then, with the increase in TEA volumes from 0.30 ml to 0.60 ml, it increases to 3.79 eV. The optical parameters such as refractive index, extinction coefficient, real and imaginary parts of dielectric constant are evaluated and their dependence on TEA is studied. The lowest electri- cal resistivity value or most conductive film is obtained using 0.30 ml TEA due to the worm-like surface morphol- ogy in the film detected from the SEM. It is seen that the use of different TEA volumes can affect the physical and electrical properties of synthesized films.
5 Acknowledgments
We would like to thank the Management Unit of Scien- tific Research Projects of Mehmet Akif Ersoy University for supporting this work financially under the project no. 0201-NAP-13..
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