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Synthesis and characterization of cadmium sulfide (CdS) thin film for solar cell applications grown by dip coating method
Materials Today: Proceedings xxx (xxxx) xxx
Contents lists available at ScienceDirect
Materials Today: Proceedings journal homepage: www.elsevier.com/locate/matpr
Synthesis and characterization of cadmium sulfide (CdS) thin film for solar cell applications grown by dip coating method L. Dhatchinamurthy a,c,⇑, P. Thirumoorthy b, L. Arunraja c, S. Karthikeyan c a
Research and Development Centre, Department of Electronics, Bharathiar University, Coimbatore 641 046, India Department of Electronics and Communication, Government Arts College, Dharmapuri 636 705, India c Department of Electronics and Communication, K.S. Rangasamy College of Arts and Science (Autonomous), Tiruchengode 637215, India b
a r t i c l e
i n f o
Article history: Received 15 April 2019 Received in revised form 17 July 2019 Accepted 27 August 2019 Available online xxxx Keywords: Band gap Cadmium Sulfide Dip coating Solar cell XRD
a b s t r a c t The CdS nanostructure thin films have been deposited on glass substrates the usage of dip coating method. The structural, optical and surface morphologies of CdS nanostructure thin film were investigated by XRD, SEM, TEM, EDAX, UV–Vis and PL spectra. The outcomes indicated the films were hexagonal shape and the grains are spherically formed and allotted uniformly over the complete surface of the glass substrate. The impact of quantum confinement and the shifts in optical band gap had been calculated. The results indicated CdS nanostructure thin film is appropriate for solar cell window layer application and the solar cell conversion efficiency was calculated. Ó 2019 Elsevier Ltd. All rights reserved. Selection and peer-review under responsibility of the scientific committee of the International Conference on Emerging Materials and Modeling.
1. Introduction Cadmium sulfide (CdS) is a semiconducting material utilized in a variety of applications. The wide band gap, low absorption loss, compact crystallographic cell structure and electronic affinity makes CdS is a promising optoelectronic device for making solar cell CISe and InP [1]. Thin films of CdS have received widespread attention in the direction of other device applications such as including electrochemical cells [2], gas sensors [3], and metalSchottky barrier cells [1]. It is mainly used as an optical window material. Nanoparticles of CdS doped with other semiconductor materials working as photo sensor detection [4], Light emitting diodes (LED) [5], Semiconductor lasers [6], Thin films transistors [7], Photo detectors [5], Photoluminescence, Photosensitization and Photocatalytic properties [8] Solar cellular [9] and gas sensor [10,11]. CdS is an important room temperature band gap of 2.42 eV (512 nm) and the potential applications of CdS have been used as a window layer in solar cell together with narrow band gap materials [12]. The energetic studies on optical and electrical properties of nanoparticles in polymeric matrices were accomplished in comparison to the polymer on my own [13]. Generally, polymers inclusive of PVA have low electrical conductivity, it behaves like
⇑ Corresponding author at: Research and Development Centre, Department of Electronics, Bharathiar University, Coimbatore 641 046, India. E-mail address: [email protected] (L. Dhatchinamurthy).
insulator. PVA is selected as capping and blending aspect wherein the polymer does now not trade the inherit traits of the inorganic phase [14]. Their electrical conductivity relies upon on the thermally generated carries and the addition of suitable dopant substances [15,16]. In unique, nanoparticle-doped polymers are considered to be a new class of inorganic/organic nanocomposites and the incorporation of these organic and inorganic phases leads to own and enhance the beneficial properties which include light weight and suitable mobility of polymers similarly to excessive strength, warmness stability and chemical resistance of inorganic materials. These modifications in physical properties rely on the chemical nature of the dopant and the way wherein they interact with the host polymer [17,18]. Among this polymer, PVA is good dielectric electricity, good storage ability in annealing dependent electrical and optical properties [19]. Furthermore this parameter is decided to synthesizing characteristics of nanostructure thin film. The various deposition strategies to put together CdS thin film including spin coating, thermal evaporation, spray pyrolysis, electro deposition and dip coding. Among this diverse thin film deposition approach the dip coating deposition system to be a easy, smooth to handle, cost effective method and wide industrial applications. The dip coating technique is containing in three parameters consisting of i) Immersion and dwell time ii) Deposition and Drainage iii) Evaporation. These three parameters have been without difficulty adjusted at some point of the film coating time.
https://doi.org/10.1016/j.matpr.2019.08.219 2214-7853/Ó 2019 Elsevier Ltd. All rights reserved. Selection and peer-review under responsibility of the scientific committee of the International Conference on Emerging Materials and Modeling.
Please cite this article as: L. Dhatchinamurthy, P. Thirumoorthy, L. Arunraja et al., Synthesis and characterization of cadmium sulfide (CdS) thin film for solar cell applications grown by dip coating method, Materials Today: Proceedings, https://doi.org/10.1016/j.matpr.2019.08.219
2
L. Dhatchinamurthy et al. / Materials Today: Proceedings xxx (xxxx) xxx
Basically the final film microstructure various with recognize of associated with evaporation rate, film thickness and surface tension of the solvent. In this research work, we have got consciousness on prepared and synthesis of CdS thin films grown on glass substrate the usage of dip coating, and analyzes at the surface morphology, crystalline structure and optical properties is observed. This approach can put together a smooth surface and transparent films thoroughly cohere to the substrate that is to be suitable for window layer in solar cell application. 2. Experimental details 2.1. Substances Cadmium acetate [Cd (CH3COO)22H2O], Thiourea [CS (NH2)2] and the Polyvinyl alcohol (PVA) having purity (>99.9%) all reagents were of analytical grade and used without further purification, which purchased from Merk India. Deionized water was used to prepare all the solutions throughout the experiments. 2.2. Synthesis of CdS nanostructure thin film Initially, 0.6 M of Cadmium acetate mixed with 25 ml of deionized water and stirring for 1 h at 40 °C. Then 1 M of thiourea combined with 25 ml of deionized water and stirring for 1 h at 40 °C. Then thiourea became mixed with cadmium acetate drop with the aid of drop and the reactants have been stirred constantly for another 1hr at 40 °C. The 5 g of PVA is blended with 100 ml of deionized water and stirred for 8 h. Then 50 ml of polymer solution (PVA) is blended with prepared precursors materials of CdS added drop wise, and then stirred with 50 °C at 24 h by 400 rpm. In this solutions had been coated on a glass substrate via dip coating method. The glass substrate is vertically immersed to the matrix solution with constant time interval of 1 h. Then the films had been dried at hot air oven at 50 °C for 1 h. The color of thin film modifications from transparent to light yellow this is indicating the formation of CdS nanostructure thin film. 2.3. Characterization The crystalline structures of the films were analyzed using Rigaku X-ray diffractometer (MiniFlex-New 6th generation general purpose benchtop XRD system for phase i.d and phase quantification). The optical studies and absorption spectra were recorded using a UV–visible spectrophotometer (Cary 8454; Agilent, Singapore) operated in the UV to near-IR (180–800) special region. Photoluminescence (PL) spectra were analyzed by Cary Eclipse, Agilent Technologies, at Singapore. The morphology, microstructure and elemental composition of all the samples were analyzed using a scanning electron microscope (SEM) coupled with energydispersive X-ray analysis (JSM 6360; JEOL, Japan). The high resolution electron microscopy images were taken by TECNAI-30 model instrument. The FTIR spectra of the films were obtained by an Agilent Technologies, Singapore, Cary 630 FTIR Spectrophotometer in the wavelength range of 4000–400 cm1.
Fig. 1. X-ray diffraction pattern of CdS nanostructure thin film.
mium sulfide phase by comparing with the standard data from JCPDS card (File No. 41-1049). The average crystalline size of the grains has been obtained from X-ray diffraction pattern by use of the Scherrer’s formula
D ¼ K´=bcosh where D is the grain size, K is constant to 0.94b is the full width at half maximum (FWHM) and ƛ is the wavelength of the X-rays. The average grain size obtained around 29 nm. The Diffraction peaks were detected at 26.66°, 43.81° and 52.31° which can be ascribed due to (0 0 2), (1 1 0) and (2 0 1) reflection planes of the hexagonal CdS structure, respectively [10–12]. The XRD revels that the CdS thin film synthesized are in the identification of excellent crystallinity nature of the film. 3.2. Structural and morphology The SEM image of CdS nanostructure thin film is shown in Fig. 2. We found that the elements are uniformly disbursed. The surface morphology clearly shows that the film is formed well covered the substrate nicely, homogeneous and small crystalline nature. The common particle size of CdS is found to be 18 nm. The analyze report was reveals that the end result is compared with the particle
3. Results and discussion 3.1. X-ray diffraction of CdS nanostructure thin film The X-ray diffraction of CdS nanostructure thin film shows in Fig. 1. It is observed that XRD patterns show a preferred orientation along (0 0 2) plane. The styles can be assigned to hexagonal cad-
Fig. 2. SEM images analysis for CdS nanostructure thin film.
Please cite this article as: L. Dhatchinamurthy, P. Thirumoorthy, L. Arunraja et al., Synthesis and characterization of cadmium sulfide (CdS) thin film for solar cell applications grown by dip coating method, Materials Today: Proceedings, https://doi.org/10.1016/j.matpr.2019.08.219
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size of 29.72 nm which was calculated by the usage of XRD analysis. Elemental composition of the samples and its purity has been validated the usage of EDAX shown in Fig. 3. In purity, the formation of cadmium (Cd) 54.92% and sulfur (S) 18.17% have been grown of CdS thin film detected indicating. The element composition observations are shown in Table 1.
Table 1 Elemental composition of CdS nanostructure thin film. Sample
Element Weight%
CdS
Cd
S
54.92
18.17
3.3. Optical studies The absorbance edge is received blue shifted. This blue shift of the absorption edge indicates decrease of the crystallite sizes of the samples. CdS is a typical direct band gap semiconductor. Fig. 4. Indicates the UV–vis absorption spectra of CdS nanostructure thin film measured the wavelength range are 481 nm. Finally the UV–vis a spectrum turned into reveals that better absorption wavelength [11,12]. The band gap and shift in band gap are given Table 2 [12]. The formation of CdS thin film is likewise confirmed through Photoluminescence Spectroscopy (PL). The PL is crucialtool for the research of optical process within semiconductor samples. Fig. 5. Shows the PL spectra of CdS nanostructure thin film for an excitation wavelength is 368 nm and located the emission peak around 426 nm (2.91 eV) [20]. The CdS nanostructure thin film emission band at around 426 nm called blue band and the broad emission peak at 532 nm have been acquired, it referred to as yellow band [12].
Fig. 4. UV–vis absorbance spectrum of CdS nanostructure thin film.
3.4. Fourier transform infrared spectroscopy (FTIR) analysis FTIR spectra of the CdS/PVA thin films are shown in Fig. 6. The various practical groups present within CdS/PVA nanostructure similar to their wave number are proven in Table 3. The peak seemed at 3414.54 cm1 indicates the presence of OH stretching. This can be due to the atmospheric moisture. The peaks at 1539.65 cm1, 1396.88 cm1 are assigned to the vibrational mode of OH bending. The peak at 1228.69 cm1 shows the presence of symmetric stretching within the molecule. The robust absorption band at 1097.35 cm1 is assigned to the symmetric stretching (C@O bond). The interaction within polymer chains is moving their position this indicates that the coordination among CdS/PVA polymer chains taken vicinity [21]. There are medium to strong absorption bands at 467.49 cm1 and 669.75 cm1 had been assigned to because of CdAS stretching. Hence the existences of above
Table 2 Band gap and shift in band gap calculated from absorption spectra. Sample
Wavelength (nm)
Band gab from UV–vis (eV)
Shift in band gab (eV)
CdS
481
2.57
0.15
Fig. 5. PL spectrum of CdS nanostructure thin film.
mentioned bands become aware of the presence of CdS and also the impurities that the samples consisted of water molecules or hydroxide ions. 3.5. TEM analysis
Fig. 3. CdS nanostructure thin film elemental analysis using EDAX.
The CdS/PVA thin film becomes morphologically investigated via transmission electron microscopy Fig. 7. The offered TEM images are well dispersed uniform size spherical can be absolutely
Please cite this article as: L. Dhatchinamurthy, P. Thirumoorthy, L. Arunraja et al., Synthesis and characterization of cadmium sulfide (CdS) thin film for solar cell applications grown by dip coating method, Materials Today: Proceedings, https://doi.org/10.1016/j.matpr.2019.08.219
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of spherical nanostructure. The Fig. 7 Shows the particles were greater discrete, however, not properly resolved because of the presence of the PVA. However the atoms have been now not aggregated proper into a massive shape, even though the particles were in contact with each other. Most of the particles were similar in size and characteristic extraordinary curved shapes. The common particle dimensions for all are grow to be calculated. The elements dimensions from TEM evaluation matched properly with the crystallite length value calculated from XRD arrangements. 3.6. Device manufacturing and IV characteristics
Fig. 6. FTIR pattern of CdS nanostructure thin film.
Table 3 Assignment of functional groups for FTIR spectra for CdS nanostructure thin film. Wavenumber (cm1) CdS
Functional group
467.49 669.75 939.89 1007.07 1097.35
CdAS stretching (CdS)
1149.84 1396.88 1539.65 1614.54 1659.33 2761.58 3061.81 3294.16 3414.54
@CH2 bending vibrations and CAH stretching out-of-plane CAH bending CAO stretching and CAOAC stretching of acetyl group present in the PVA backbone Traces of SO 4 ion as impurity CAOAH bending C@C (in ring) (2 bands) C@C terminal Bending (OAH) CAH (aldehyde CAH) CAH bonds hydroxyl (AOH) groups OAH Stretching and primary amide NH2
The CdS/PVA/CdTe solar cell became fabricated the usage of dip deposition technique of CdS/PVA nanocomposite thin films. The structures of the cells are shown in Fig. 8. It has made from four layers. The first layer of glass substrate was enclosed by way of 250 nm thick layer of transparent conducting oxide (ITO). The CdS/PVA nanocomposite thin film was then deposited on the top of ITO to a thickness of approximately 50 nm. Before deposition of CdTe, CdS/PVA film becomes annealed for 30 min at 50 °C. A layer of CdTe of thickness 500 nm was then thermally evaporated at the top at a base strain <106 mbar. Before making the top contact, CdTe turned into dealt with CdCl2 at 200 °C in a tube furnace for one hour under ambient conditions. The CdCl2 usage is critical as it improves the crystalline quality of CdTe through growing the scale of small grains and with the aid of doing away with numerous defects in the materials. After CdCl2 treatment, CdTe turned into etched in a combination of nitric acids and phosphoric acid to keep away from the formation of undesirable CdO or CdTeO3 on CdTe surface for you to make good contact on CdTe. Finally, a layer of HgTe became deposited on the top as a back contact via thermal evaporation method at a pressure <106 mbar. The device had an area of 2 2 cm2 and found stable for three month. The current-voltage (I-V) characteristics of the CdS/PVA solar cell were measured with high impedance (1014) ECIL electrometer amplifier is shown in Fig. 9. The intensity of illumination was measured with Altron LX-101 lx meter. The solar cell parameter turned into measured underneath illumination with a 50 mW Cm2 tungsten lamp. The efficiency of a solar cell is determined as the fraction of incident power which is converted to electricity. The solar cell conversion efficiency has been obtained from I-V characteristics by use of this formula
g ¼ Voc Isc FF=Pin
Fig. 7. TEM analysis of CdS nanostructure thin film.
seen inside the TEM photograph with quite even size distribution and no agglomeration is determined inside the image. Based on acquiring TEM image, PVA plays an important role in the growth
Fig. 8. Structure of CdS/PVA-CdTe solar cell.
Please cite this article as: L. Dhatchinamurthy, P. Thirumoorthy, L. Arunraja et al., Synthesis and characterization of cadmium sulfide (CdS) thin film for solar cell applications grown by dip coating method, Materials Today: Proceedings, https://doi.org/10.1016/j.matpr.2019.08.219
L. Dhatchinamurthy et al. / Materials Today: Proceedings xxx (xxxx) xxx
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Acknowledgements The author is thankful to the Management and Principal of K. S. Rangasamy College of Arts and Science College (Autonomous), Tiruchengode, Tamilnadu, India for providing facilities to conduct this research work. References [1] [2] [3] [4] [5] [6] [7] [8] [9] [10] Fig. 9. I-V characteristics of CdS/PVA-CdTe solar cell.
[11] [12]
where Voc is the open-circuit voltage, Isc is the short-circuit current, FF is the fill factor and g is the efficiency. A cell conversion efficiency of 4.81% (Voc = 0.632 V, Jsc = 95lA/cm2, FF = 0.60) has been achieved from the CdS/PVA window layer [22,23]. 4. Conclusion Cadmium sulfide thin films are prepared from cadmium acetate and thiourea at room temperature on glass substrates using dip coating technique. The XRD results obtained the hexagonal phase of CdS nanostructure thin film are showed better structural, optical and morphological properties. The optical absorbance spectra obtained from the films are used to favorable optical band gap which is very useful for solar cell window layer applications. The efficiency of CdS nanostructure thin film was calculated.
[13] [14] [15] [16] [17] [18] [19] [20] [21]
[22] [23]
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Please cite this article as: L. Dhatchinamurthy, P. Thirumoorthy, L. Arunraja et al., Synthesis and characterization of cadmium sulfide (CdS) thin film for solar cell applications grown by dip coating method, Materials Today: Proceedings, https://doi.org/10.1016/j.matpr.2019.08.219
Contents lists available at ScienceDirect
Materials Today: Proceedings journal homepage: www.elsevier.com/locate/matpr
Synthesis and characterization of cadmium sulfide (CdS) thin film for solar cell applications grown by dip coating method L. Dhatchinamurthy a,c,⇑, P. Thirumoorthy b, L. Arunraja c, S. Karthikeyan c a
Research and Development Centre, Department of Electronics, Bharathiar University, Coimbatore 641 046, India Department of Electronics and Communication, Government Arts College, Dharmapuri 636 705, India c Department of Electronics and Communication, K.S. Rangasamy College of Arts and Science (Autonomous), Tiruchengode 637215, India b
a r t i c l e
i n f o
Article history: Received 15 April 2019 Received in revised form 17 July 2019 Accepted 27 August 2019 Available online xxxx Keywords: Band gap Cadmium Sulfide Dip coating Solar cell XRD
a b s t r a c t The CdS nanostructure thin films have been deposited on glass substrates the usage of dip coating method. The structural, optical and surface morphologies of CdS nanostructure thin film were investigated by XRD, SEM, TEM, EDAX, UV–Vis and PL spectra. The outcomes indicated the films were hexagonal shape and the grains are spherically formed and allotted uniformly over the complete surface of the glass substrate. The impact of quantum confinement and the shifts in optical band gap had been calculated. The results indicated CdS nanostructure thin film is appropriate for solar cell window layer application and the solar cell conversion efficiency was calculated. Ó 2019 Elsevier Ltd. All rights reserved. Selection and peer-review under responsibility of the scientific committee of the International Conference on Emerging Materials and Modeling.
1. Introduction Cadmium sulfide (CdS) is a semiconducting material utilized in a variety of applications. The wide band gap, low absorption loss, compact crystallographic cell structure and electronic affinity makes CdS is a promising optoelectronic device for making solar cell CISe and InP [1]. Thin films of CdS have received widespread attention in the direction of other device applications such as including electrochemical cells [2], gas sensors [3], and metalSchottky barrier cells [1]. It is mainly used as an optical window material. Nanoparticles of CdS doped with other semiconductor materials working as photo sensor detection [4], Light emitting diodes (LED) [5], Semiconductor lasers [6], Thin films transistors [7], Photo detectors [5], Photoluminescence, Photosensitization and Photocatalytic properties [8] Solar cellular [9] and gas sensor [10,11]. CdS is an important room temperature band gap of 2.42 eV (512 nm) and the potential applications of CdS have been used as a window layer in solar cell together with narrow band gap materials [12]. The energetic studies on optical and electrical properties of nanoparticles in polymeric matrices were accomplished in comparison to the polymer on my own [13]. Generally, polymers inclusive of PVA have low electrical conductivity, it behaves like
⇑ Corresponding author at: Research and Development Centre, Department of Electronics, Bharathiar University, Coimbatore 641 046, India. E-mail address: [email protected] (L. Dhatchinamurthy).
insulator. PVA is selected as capping and blending aspect wherein the polymer does now not trade the inherit traits of the inorganic phase [14]. Their electrical conductivity relies upon on the thermally generated carries and the addition of suitable dopant substances [15,16]. In unique, nanoparticle-doped polymers are considered to be a new class of inorganic/organic nanocomposites and the incorporation of these organic and inorganic phases leads to own and enhance the beneficial properties which include light weight and suitable mobility of polymers similarly to excessive strength, warmness stability and chemical resistance of inorganic materials. These modifications in physical properties rely on the chemical nature of the dopant and the way wherein they interact with the host polymer [17,18]. Among this polymer, PVA is good dielectric electricity, good storage ability in annealing dependent electrical and optical properties [19]. Furthermore this parameter is decided to synthesizing characteristics of nanostructure thin film. The various deposition strategies to put together CdS thin film including spin coating, thermal evaporation, spray pyrolysis, electro deposition and dip coding. Among this diverse thin film deposition approach the dip coating deposition system to be a easy, smooth to handle, cost effective method and wide industrial applications. The dip coating technique is containing in three parameters consisting of i) Immersion and dwell time ii) Deposition and Drainage iii) Evaporation. These three parameters have been without difficulty adjusted at some point of the film coating time.
https://doi.org/10.1016/j.matpr.2019.08.219 2214-7853/Ó 2019 Elsevier Ltd. All rights reserved. Selection and peer-review under responsibility of the scientific committee of the International Conference on Emerging Materials and Modeling.
Please cite this article as: L. Dhatchinamurthy, P. Thirumoorthy, L. Arunraja et al., Synthesis and characterization of cadmium sulfide (CdS) thin film for solar cell applications grown by dip coating method, Materials Today: Proceedings, https://doi.org/10.1016/j.matpr.2019.08.219
2
L. Dhatchinamurthy et al. / Materials Today: Proceedings xxx (xxxx) xxx
Basically the final film microstructure various with recognize of associated with evaporation rate, film thickness and surface tension of the solvent. In this research work, we have got consciousness on prepared and synthesis of CdS thin films grown on glass substrate the usage of dip coating, and analyzes at the surface morphology, crystalline structure and optical properties is observed. This approach can put together a smooth surface and transparent films thoroughly cohere to the substrate that is to be suitable for window layer in solar cell application. 2. Experimental details 2.1. Substances Cadmium acetate [Cd (CH3COO)22H2O], Thiourea [CS (NH2)2] and the Polyvinyl alcohol (PVA) having purity (>99.9%) all reagents were of analytical grade and used without further purification, which purchased from Merk India. Deionized water was used to prepare all the solutions throughout the experiments. 2.2. Synthesis of CdS nanostructure thin film Initially, 0.6 M of Cadmium acetate mixed with 25 ml of deionized water and stirring for 1 h at 40 °C. Then 1 M of thiourea combined with 25 ml of deionized water and stirring for 1 h at 40 °C. Then thiourea became mixed with cadmium acetate drop with the aid of drop and the reactants have been stirred constantly for another 1hr at 40 °C. The 5 g of PVA is blended with 100 ml of deionized water and stirred for 8 h. Then 50 ml of polymer solution (PVA) is blended with prepared precursors materials of CdS added drop wise, and then stirred with 50 °C at 24 h by 400 rpm. In this solutions had been coated on a glass substrate via dip coating method. The glass substrate is vertically immersed to the matrix solution with constant time interval of 1 h. Then the films had been dried at hot air oven at 50 °C for 1 h. The color of thin film modifications from transparent to light yellow this is indicating the formation of CdS nanostructure thin film. 2.3. Characterization The crystalline structures of the films were analyzed using Rigaku X-ray diffractometer (MiniFlex-New 6th generation general purpose benchtop XRD system for phase i.d and phase quantification). The optical studies and absorption spectra were recorded using a UV–visible spectrophotometer (Cary 8454; Agilent, Singapore) operated in the UV to near-IR (180–800) special region. Photoluminescence (PL) spectra were analyzed by Cary Eclipse, Agilent Technologies, at Singapore. The morphology, microstructure and elemental composition of all the samples were analyzed using a scanning electron microscope (SEM) coupled with energydispersive X-ray analysis (JSM 6360; JEOL, Japan). The high resolution electron microscopy images were taken by TECNAI-30 model instrument. The FTIR spectra of the films were obtained by an Agilent Technologies, Singapore, Cary 630 FTIR Spectrophotometer in the wavelength range of 4000–400 cm1.
Fig. 1. X-ray diffraction pattern of CdS nanostructure thin film.
mium sulfide phase by comparing with the standard data from JCPDS card (File No. 41-1049). The average crystalline size of the grains has been obtained from X-ray diffraction pattern by use of the Scherrer’s formula
D ¼ K´=bcosh where D is the grain size, K is constant to 0.94b is the full width at half maximum (FWHM) and ƛ is the wavelength of the X-rays. The average grain size obtained around 29 nm. The Diffraction peaks were detected at 26.66°, 43.81° and 52.31° which can be ascribed due to (0 0 2), (1 1 0) and (2 0 1) reflection planes of the hexagonal CdS structure, respectively [10–12]. The XRD revels that the CdS thin film synthesized are in the identification of excellent crystallinity nature of the film. 3.2. Structural and morphology The SEM image of CdS nanostructure thin film is shown in Fig. 2. We found that the elements are uniformly disbursed. The surface morphology clearly shows that the film is formed well covered the substrate nicely, homogeneous and small crystalline nature. The common particle size of CdS is found to be 18 nm. The analyze report was reveals that the end result is compared with the particle
3. Results and discussion 3.1. X-ray diffraction of CdS nanostructure thin film The X-ray diffraction of CdS nanostructure thin film shows in Fig. 1. It is observed that XRD patterns show a preferred orientation along (0 0 2) plane. The styles can be assigned to hexagonal cad-
Fig. 2. SEM images analysis for CdS nanostructure thin film.
Please cite this article as: L. Dhatchinamurthy, P. Thirumoorthy, L. Arunraja et al., Synthesis and characterization of cadmium sulfide (CdS) thin film for solar cell applications grown by dip coating method, Materials Today: Proceedings, https://doi.org/10.1016/j.matpr.2019.08.219
3
L. Dhatchinamurthy et al. / Materials Today: Proceedings xxx (xxxx) xxx
size of 29.72 nm which was calculated by the usage of XRD analysis. Elemental composition of the samples and its purity has been validated the usage of EDAX shown in Fig. 3. In purity, the formation of cadmium (Cd) 54.92% and sulfur (S) 18.17% have been grown of CdS thin film detected indicating. The element composition observations are shown in Table 1.
Table 1 Elemental composition of CdS nanostructure thin film. Sample
Element Weight%
CdS
Cd
S
54.92
18.17
3.3. Optical studies The absorbance edge is received blue shifted. This blue shift of the absorption edge indicates decrease of the crystallite sizes of the samples. CdS is a typical direct band gap semiconductor. Fig. 4. Indicates the UV–vis absorption spectra of CdS nanostructure thin film measured the wavelength range are 481 nm. Finally the UV–vis a spectrum turned into reveals that better absorption wavelength [11,12]. The band gap and shift in band gap are given Table 2 [12]. The formation of CdS thin film is likewise confirmed through Photoluminescence Spectroscopy (PL). The PL is crucialtool for the research of optical process within semiconductor samples. Fig. 5. Shows the PL spectra of CdS nanostructure thin film for an excitation wavelength is 368 nm and located the emission peak around 426 nm (2.91 eV) [20]. The CdS nanostructure thin film emission band at around 426 nm called blue band and the broad emission peak at 532 nm have been acquired, it referred to as yellow band [12].
Fig. 4. UV–vis absorbance spectrum of CdS nanostructure thin film.
3.4. Fourier transform infrared spectroscopy (FTIR) analysis FTIR spectra of the CdS/PVA thin films are shown in Fig. 6. The various practical groups present within CdS/PVA nanostructure similar to their wave number are proven in Table 3. The peak seemed at 3414.54 cm1 indicates the presence of OH stretching. This can be due to the atmospheric moisture. The peaks at 1539.65 cm1, 1396.88 cm1 are assigned to the vibrational mode of OH bending. The peak at 1228.69 cm1 shows the presence of symmetric stretching within the molecule. The robust absorption band at 1097.35 cm1 is assigned to the symmetric stretching (C@O bond). The interaction within polymer chains is moving their position this indicates that the coordination among CdS/PVA polymer chains taken vicinity [21]. There are medium to strong absorption bands at 467.49 cm1 and 669.75 cm1 had been assigned to because of CdAS stretching. Hence the existences of above
Table 2 Band gap and shift in band gap calculated from absorption spectra. Sample
Wavelength (nm)
Band gab from UV–vis (eV)
Shift in band gab (eV)
CdS
481
2.57
0.15
Fig. 5. PL spectrum of CdS nanostructure thin film.
mentioned bands become aware of the presence of CdS and also the impurities that the samples consisted of water molecules or hydroxide ions. 3.5. TEM analysis
Fig. 3. CdS nanostructure thin film elemental analysis using EDAX.
The CdS/PVA thin film becomes morphologically investigated via transmission electron microscopy Fig. 7. The offered TEM images are well dispersed uniform size spherical can be absolutely
Please cite this article as: L. Dhatchinamurthy, P. Thirumoorthy, L. Arunraja et al., Synthesis and characterization of cadmium sulfide (CdS) thin film for solar cell applications grown by dip coating method, Materials Today: Proceedings, https://doi.org/10.1016/j.matpr.2019.08.219
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L. Dhatchinamurthy et al. / Materials Today: Proceedings xxx (xxxx) xxx
of spherical nanostructure. The Fig. 7 Shows the particles were greater discrete, however, not properly resolved because of the presence of the PVA. However the atoms have been now not aggregated proper into a massive shape, even though the particles were in contact with each other. Most of the particles were similar in size and characteristic extraordinary curved shapes. The common particle dimensions for all are grow to be calculated. The elements dimensions from TEM evaluation matched properly with the crystallite length value calculated from XRD arrangements. 3.6. Device manufacturing and IV characteristics
Fig. 6. FTIR pattern of CdS nanostructure thin film.
Table 3 Assignment of functional groups for FTIR spectra for CdS nanostructure thin film. Wavenumber (cm1) CdS
Functional group
467.49 669.75 939.89 1007.07 1097.35
CdAS stretching (CdS)
1149.84 1396.88 1539.65 1614.54 1659.33 2761.58 3061.81 3294.16 3414.54
@CH2 bending vibrations and CAH stretching out-of-plane CAH bending CAO stretching and CAOAC stretching of acetyl group present in the PVA backbone Traces of SO 4 ion as impurity CAOAH bending C@C (in ring) (2 bands) C@C terminal Bending (OAH) CAH (aldehyde CAH) CAH bonds hydroxyl (AOH) groups OAH Stretching and primary amide NH2
The CdS/PVA/CdTe solar cell became fabricated the usage of dip deposition technique of CdS/PVA nanocomposite thin films. The structures of the cells are shown in Fig. 8. It has made from four layers. The first layer of glass substrate was enclosed by way of 250 nm thick layer of transparent conducting oxide (ITO). The CdS/PVA nanocomposite thin film was then deposited on the top of ITO to a thickness of approximately 50 nm. Before deposition of CdTe, CdS/PVA film becomes annealed for 30 min at 50 °C. A layer of CdTe of thickness 500 nm was then thermally evaporated at the top at a base strain <106 mbar. Before making the top contact, CdTe turned into dealt with CdCl2 at 200 °C in a tube furnace for one hour under ambient conditions. The CdCl2 usage is critical as it improves the crystalline quality of CdTe through growing the scale of small grains and with the aid of doing away with numerous defects in the materials. After CdCl2 treatment, CdTe turned into etched in a combination of nitric acids and phosphoric acid to keep away from the formation of undesirable CdO or CdTeO3 on CdTe surface for you to make good contact on CdTe. Finally, a layer of HgTe became deposited on the top as a back contact via thermal evaporation method at a pressure <106 mbar. The device had an area of 2 2 cm2 and found stable for three month. The current-voltage (I-V) characteristics of the CdS/PVA solar cell were measured with high impedance (1014) ECIL electrometer amplifier is shown in Fig. 9. The intensity of illumination was measured with Altron LX-101 lx meter. The solar cell parameter turned into measured underneath illumination with a 50 mW Cm2 tungsten lamp. The efficiency of a solar cell is determined as the fraction of incident power which is converted to electricity. The solar cell conversion efficiency has been obtained from I-V characteristics by use of this formula
g ¼ Voc Isc FF=Pin
Fig. 7. TEM analysis of CdS nanostructure thin film.
seen inside the TEM photograph with quite even size distribution and no agglomeration is determined inside the image. Based on acquiring TEM image, PVA plays an important role in the growth
Fig. 8. Structure of CdS/PVA-CdTe solar cell.
Please cite this article as: L. Dhatchinamurthy, P. Thirumoorthy, L. Arunraja et al., Synthesis and characterization of cadmium sulfide (CdS) thin film for solar cell applications grown by dip coating method, Materials Today: Proceedings, https://doi.org/10.1016/j.matpr.2019.08.219
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Acknowledgements The author is thankful to the Management and Principal of K. S. Rangasamy College of Arts and Science College (Autonomous), Tiruchengode, Tamilnadu, India for providing facilities to conduct this research work. References [1] [2] [3] [4] [5] [6] [7] [8] [9] [10] Fig. 9. I-V characteristics of CdS/PVA-CdTe solar cell.
[11] [12]
where Voc is the open-circuit voltage, Isc is the short-circuit current, FF is the fill factor and g is the efficiency. A cell conversion efficiency of 4.81% (Voc = 0.632 V, Jsc = 95lA/cm2, FF = 0.60) has been achieved from the CdS/PVA window layer [22,23]. 4. Conclusion Cadmium sulfide thin films are prepared from cadmium acetate and thiourea at room temperature on glass substrates using dip coating technique. The XRD results obtained the hexagonal phase of CdS nanostructure thin film are showed better structural, optical and morphological properties. The optical absorbance spectra obtained from the films are used to favorable optical band gap which is very useful for solar cell window layer applications. The efficiency of CdS nanostructure thin film was calculated.
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Please cite this article as: L. Dhatchinamurthy, P. Thirumoorthy, L. Arunraja et al., Synthesis and characterization of cadmium sulfide (CdS) thin film for solar cell applications grown by dip coating method, Materials Today: Proceedings, https://doi.org/10.1016/j.matpr.2019.08.219