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SYNTHESIS AND CHARACTERIZATION OF POLYMER-CdSe NANOCOMPOSITE FILM AND ITS PHOTOVOLTAIC STUDIES
IN PHOTOELECTROCHEMICAL SOLAR CELL
SWATI DUBEY, MEERA RAMRAKHIANI Department of Physics & Electronics
Rani Durgawati University Jabalpur- 482001, India
*corresponding author: Swatidb22@gmail.com
HIGHLIGHTS
Photovoltaic effect, CdSe/PVA nano composite, Photo-electrochemical solar cells, XRD, SEM, Absorption spectra
ABSTRACT
Solar cell generates electricity with no global warming pollution, no fuel costs, and no risks of fuel price spikes, and has the potential to help move the country toward cleaner, reliable, and affordable sources of electricity. The development of thin film solar cell is an active area of research at this time, using nanocrystalline thin film technology. This study presents the results of a research aimed at improving integration and stability in nanocrystal-based solar cells through advances in active materials and device architectures.
Cadmium Selenide (CdSe) is an important II-VI semiconducting compound with a direct band gap energy of 1.74 eV. Due to high absorption coefficient and favorable optical properties, CdSe thin film find application in Photoelectrochemical solar cell (PEC), optoelectronic devices, gamma ray detectors, light emitting diodes, solar cells, photodetectors, electrophotography and in laser. Cadmium selenide (CdSe) nanoparticle has been synthesized by a simple chemical route using polymer as a host matrix. Polyvinal alcohol (PVA) was used as a stabilizer as well as host matrix to prevent agglomeration of nanoparticles. The formation of CdSe/PVA nanocomposite was further confirmed by Photovoltaic, UV-visible, XRD, SEM. The energy band gap of film is determined by absorption spectra in wavelength range 200–900 nm. The XRD result reveals that synthesized CdSe nanoparticle have hexagonal phase.
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The appearance of many peaks in the XRD pattern is an indication of nanocrystalline nature of CdSe thin film with particle size 5.41nm. SEM image confirmed a uniform distribution of the embedded CdSe nanoparticle in composite film. Photoelectrochemical cell (PEC) using nanocrystal polymer composites of CdSe/PVA has been successfully prepared by simple chemical route deposited on titanium substrate was investigated. Film was annealed at 150°C for 1:30 hour used as photo-electrode in photoelectrochemical cell having polysulfide electrolyte solution and graphite as counter electrode. The CdSe/PVA photo-electrode was illuminated by 50 watt tungsten lamp. Using a potentiometer, the photo-voltage & photo-current were measured at different load resistances and solar cell parameters were determined. The results indicate that CdSe/PVA nanocomposite exhibit photovoltaic effect in PEC cell and may be a candidate for low cost solar cells in order to convert solar energy into electrical energy.
1INTRODUCTION:
Nanocomposites of II-VI inorganic semiconductors dispersed in
polymer matrices are
multifunctional materials. The development of composites consisting of a continuous matrix with dispersed nanoparticles[1] of II- VI semiconductor nanocrystals and studies of their optical properties are now a day’s important activities in optoelectronic devices such as blue-green laser diodes (LDs), white light emitting diodes (LEDs), optically controlled switches tunable mid-IR laser sources for
remote sensing applications photovoltaic and photo electro- chemical[2-3] devices. Cadmium selenide (CdSe) having band gap 1.7eV is a good candidate for photovoltaic cell [4]. In present work polymer selenide composites are prepared via a two-stage process including the synthesis of selenide nanocrystals and polymer separately, followed by the dispersion of the selenide into the polymer matrix their performance in PEC cells with polysulfide electrolyte has been studied.
3 2 EXPERIMENTAL:
2.1 SYNTHESIS:
CdSe/PVA nanocomposite thin film has been prepared by chemical
method. Cadmium
chloride(CdCl2.2H2O) was chosen as metal ion source and sodium selenosulphate (Na2SeSO3) was chosen as selenium source, and polyvinyl alcohol (PVA) was chosen as stabilizer due to its aqueous stability. First of all a 100 ml aqueous solution of sodium sulfite (1M) was prepared. Then 0.1 mol of selenium powder was added with constant stirring, the mixture was heated to 60°C till the selenium is dissolved in the solution. Upon filtration, sodium selenosulfate solution, was obtained. PVA solution was prepared by adding 3 gm PVA in 50 ml distilled water and stirring at 90°C until a viscous transparent solution was obtained. Ammonia solution was used as a complexing agent. Prepared solution was deposited on glass plate and annealed at 150°c for 1:30 hours.
2.2 CHARACTERIZATION: The sample was characterized by X-ray
diffraction (XRD) and SEM. Sample was characterized at SAIF Cochin STIC. XRD is one of the most powerful and established technique for material structural analysis capable of providing information about the structure of a material at atomic level. X-ray source is Cu, wavelength 1.5406Å, configuration is vertical , Theta /2 Theta geometry. X-ray model using here is Bruker AXS D8 Advance. Maximum usable angular range is 30 to 1350. The particle size was calculated using Debye-Scherrer’s formula. In order to investigate the surface morphology the sample was analyzed by scanning electron microscope The study has been done by The SEM –EDS installed in SAIF , STIC have the following specification used for analysis ; image modes- SEI,BEI ; EDS Make :JEOL Model JED-2300. For optical studies, absorption spectra was recorded with systronics double beam UV-Vis spectrometer. UV-Vis spectroscopy is the measurement of attenuating of a beam of light after it passes through a sample and the particle size is computed using
4 effective mass theory from band gap information .
3 RESULTS AND DISCUSSION:
Structural Characteristics Of The Film : The crystalline structure of CdSe thin film prepared by chemical technique on glass substrate shown in fig.1. The XRD result reveals that synthesized CdSe nanoparticle have hexagonal phase
with peaks at
2θ=19.980°,28.087°,32.179°,33.952 0, 38.718°, 59.561° and can be
ascribed due to reflections from (100), (002), (110),(102),(112) and (210) planes respectively. The particle size was calculated 5.41nm using Debye-Scherrer’s formula. It has been concluded that the deposited CdSe thin films are nanocrystalline in nature with hexagonal structure. The broad and low intense peaks may be attributed due to the formation of small size nanoparticles in CdSe thin film. The diffraction pattern shown in fig .1
Fig : 1 Diffraction Pattern of CdSe/PVA Nanocomposite Film
CdSe 150 deg Annealed
Operations: Smooth 0.150 | Background 8.128,1.000 | Import 3)
2) 1)
File: SAIFXR150914C-14(Cd Se 150 deg Annealed).raw - Step: 0.020 ° - Step time: 29.1 s - WL1: 1.5406 - kA2 Ratio: 0.5 - Generator kV: 40 kV - Generator mA: 35 mA - Type
Obs. Max: 59.567 ° - FWHM: 0.346 ° - Raw Area: 4.057 Cps x deg.
Obs. Max: 38.718 ° - FWHM: 0.281 ° - Raw Area: 4.915 Cps x deg.
Obs. Max: 32.179 ° - FWHM: 0.192 ° - Raw Area: 8.702 Cps x deg.
Lin (Counts)
0 1000 2000 3000 4000
2-Theta - Scale
10 20 30 40 50 60 70 80
2th=11.762 °,d=7.51784 2th=19.980 °,d=4.44032 2th=22.879 °,d=3.88388 2th=28.087 °,d=3.17441 2th=32.190 °,d=2.77858 2th=33.952 °,d=2.63828 2th=38.717 °,d=2.32382 2th=55.320 °,d=1.65932 2th=59.561 °,d=1.55091
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Fig 2: SEM Image Surface Morphology :
The Scanning Electron Micrographs of as deposited CdSe/PVA nanocomposite thin film is shown in Fig.2. This SEM image indicates that the CdSe nanoparticles were well dispersed in the PVA matrix.
Optical Studies : Fig 3 shows the UV-Vis absorption spectra for CdSe/PVA nanocomposite in the range .400-900nm. it can be seen from spectra that there is slight increase in absorption startating
from 700nm to 450nm. Absorption increase in the UV region and a peak is obtained below 625 nm and giving effective band gap around 1.98ev. Particle size of nanocomposites from absorption spectra is ( 5.51nm) from the increase in effective band gap in nanocrystals, which is nearly same as obtained by XRD. Nanocomposite particle size was calculated using this relation[5].
𝑟 = 2𝜋2ℏ2𝐸𝑔𝑏𝑢𝑙𝑘
1𝑚 ∗𝑒 + 1𝑚 ∗ℎ (𝐸2𝑔𝑛𝑎𝑛𝑜 − 𝐸2𝑔𝑏𝑢𝑙𝑘)𝑚0 Where Egnano is nanocomposite band
gap, Egbulk is bulk bandgap of CdSe,
m*e , m*h effective mass of electron and hole of CdSe nanoparticle.
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Figure 3 Absorption Spectra of CdSe/ PVA nanocomposite film Table 1: Particle Size from band gap information
PHOTOVOLTAIC MEASUREMENT:
Photovoltaic effect of CdSe /PVA nanocrystalline film was studied in two-electrode configuration with polysulfide electrolyte and graphite as counter electrode. Prepared CdSe/PVA nanocomposite film deposited on titanium substrate used as photo electrode in PEC cell configuration. Polysulphide
electrolyte was prepared from 1M solutions of NaOH, Na2S and sulfur.
The photo electrode was illuminated by a 50 watt halogen-tungsten lamp and current-voltage characteristics were obtained using potentiometer and multimeters. During photovoltaic measurement open circuit voltage Voc & Short circuit current Isc were measured.
1.5 2 2.5 3 3.5 4 4.5
300 400 500 600 700 800 900
Absorbance
Wavelength λ (nm)
x=0.0
Sample Bulk band gap Eg (eV)
Band gap from UV-vis spectra Egnano (eV)
Shift in band gap (ev)
Particle size from
absorption spectra
Particle size from XRD
CdSe/PVA 1.74 1.98 0.24 5.51(nm) 5.41(nm)
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Table 2: Photovoltaic parameter from V-I curve
CONCLUSION: Hexagonal phase CdSe nanoparticle with particle size of ~5.41nm in diameter have been synthesized in PVA matrix by a simple chemical method. The particle size of the CdSe nanoparticle obtained from XRD and absorption spectra was found to be in close proximity . The evolution of the CdSe nanoparticle during the
progress of the reaction was investigated with the help of the UV- Vis absorption spectroscopy and it shows that PVA has supported in restricting the final size of the particles and thereby preventing aggregation of nanoparticles. The present work may provide information regarding optical and electrical properties of
0 5 10 15 20 25 30 35 40 45
0 30 60 90 120 150 180 210 240 270 300 330 360 390 420 450 480
Current µA
Voltage (mV)
DISTAN CE FROM THE SOURC E (cm)
INTENSIT IES (LUX)
OPEN CIRCUIT VOLTAG E VOC
(mv)
SHOR T CIRCU IT CURR ENT ISC (µa)
FILL FACTO R FF%
EFFEICIE NCY η %
10 315 482 42 0.105 2.1
8 nanocomposite having binary chalcogenide CdSe in PVA. The synthesis and the applications of hybrid organic-inorganic nanostructured material is described in this work , which will be a step towards obtaining ; low cost, high efficiency, and long life solar cell.
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