International Journal of Engineering and Science Invention (IJESI) is an international journal intended for professionals and researchers in all fields of computer science and electronics. IJESI publishes research articles and reviews within the whole field Engineering Science and Technology, new teaching methods, assessment, validation and the impact of new technologies and it will continue to provide information on the latest trends and developments in this ever-expanding subject. The publications of papers are selected through double peer reviewed to ensure originality, relevance, and readability. The articles published in our journal can be accessed online.

1. International Journal of Engineering Science Invention
ISSN (Online): 2319 – 6734, ISSN (Print): 2319 – 6726
www.ijesi.org Volume 2 Issue 7 ǁ July. 2013 ǁ PP.101-104
www.ijesi.org 101 | Page
Silver nanoparticles to enhance the efficiency of silicon solar cells
1
Santanu Maity, 2
Sahadev Roy, 3
Abhishek Kumar
1,2
(Electronics and communication Engineering, National Institute of Technology, Arunachal Pradesh, Itanagar,
India)
3
(Electrical and Electronics Engineering, National Institute of Technology, Arunachal Pradesh, Itanagar, India)
ABSTRACT: Three major criteria are to be fulfilled for achieving high conversion efficiency in silicon solar
cells. They are injection of maximum optical power of the incident solar spectrum into the silicon, trapping of
optical power for maximum absorption inside silicon and efficient collection of the photo generated carriers.
Photon injection into the silicon solar cell is maximized with the help of anti reflection coatings on the silicon
surface which balances the refractive index mismatch between air and silicon. Absorption inside the cell may be
maximized by obliqueness of the light and multiple reflections inside the cell resulting in path length
enhancement. The obliqueness of light also results in a higher collection efficiency of the photo generated
carriers as the absorption takes place near the junction. To reduce the cost of such cells, there is a need for
more efficient use of the active silicon material. Advancements in nanotechnology have led to a new research
area for utilizing nano photonics for increasing the efficiency of existing solar cells. The use of metallic
nanoparticles on the front surface of silicon solar cells fulfills all the three criteria for achieving high efficiency
solar cells.
KEYWORDS: external quantum efficiency, plasma ionic effect, reflectance, nano particles
I. INTRODUCTION
Plasmonic structures can offer the possibility of reducing the physical thickness of the photovoltaic absorber
layers while remaining optically thick. Metallic nanoparticles can be used as subwavelength scattering elements
to couple freely propagating plane waves in sunlight into guided modes of an absorbing semiconductor thin
film[1]. Thin film solar cells show promise as economic alternatives to conventional silicon-wafer-based
photovoltaics, combining high efficiency with low processing and materials costs[2]. and thin film cells of
CdTe[3], amorphous Si [4] and CuInxGa1-xSe2[5,6] (CIGS) have been fabricated with absorbing layers a few
micrometers thick. In conventional cell designs, efficiencies of nanometer- thickness cells are strongly limited
by decreased absorption, carrier excitation, and photocurrent generation, and so new strategies for enhanced
absorption and light trapping are desirable[7,8] . Metallic nanostructured thin films, which support surface
plasmon polaritons (SPPs), have the potential to confine and guide incident sunlight into wavelength-scale or
subwave- length thickness absorber layer volumes[ 9] SPPs are collective oscillations of free electrons at the
boundary of a metal and a nonconducting metalic or semiconductor material[10-12]. optical excitation of SPPs
has been performed by prism coupling [13,14] and more recently by gratings[15] which can be highly efficient
but limited in both wavelength and angular range. The diffraction and scattering of small apertures have been
studied for a number of years [16, 17] with particular attention recently to the transmission properties of holes
and slits. Plasmonic scattering from the metal nanoparticles when coupled to the underlined silicon results in
increased injection. The angular spread of the scattering results in path length enhancement with better
absorption and better collection. But the ohmic loss present in metallic nanoparticles is seemed to degrade the
performance of conventional nitride coated silicon solar cells in the wavelength region of 300-1100nm.
However, replacing metallic small size nanoparticles with metalic big size nanoparticles avoids the loss
of energy due to joule heating as most conventional metalics are lossless in the wavelength region of 300-
1100nm. The application of such lossless metalic nanoparticles with optimum surface coverage on the top
surface of the solar cell substantially improves the photon injection but do not produce large angular scattering
for light trapping. However, light trapping inside the solar cell is achieved by embedding metalic nanoparticles
in the active silicon layer. The angular scattering from the metallic nanoparticles is enhanced as the mismatch in
refractive index with the embedding medium is maximized. In this paper, we study the comparative roles of
metal and metalic nanoparticles atop and embedded in the silicon substrate in enhancing the efficiency of silicon
solar cells. It is seen that a maximum relative improvement in efficiency of 28.4% is achieved for optimum
design conditions in case of 2µm thick silicon solar cell with optimized metallic nanoparticle coating atop the
silicon for maximized photon transmission and embedded metallic nanoparticles for large angular scattering.

2. Silver nanoparticles to enhance the efficiency ……
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II. EXPERIMENTAL DISCUSSION
Silver nitrate AgNO3 (Sigma Aldrich, UK) and trisodium citrate C6H5O7Na3 (Sigma Aldrich, UK) of
analytical grade purity, were used as starting materials without further purification. For making solution
deionised water (DI -water) of 18.2 MΩ-cm is taken. The silver colloid was prepared by using chemical
reduction method according to the description of Lee and Meisel [18].
Figure 1: Experimental setup for Ag nano particle reduction
The AgNO3 was dissolved in de-ionized water in a beaker. In experiment 250 ml of 20 mg AgNO3
was heated to boiling. To this solution 5 ml of 1 % trisodium citrate was added drop by drop. During the process
solution was mixed vigorously using magnetic starrer. Solution was heated until color’s change is evident (pale
yellow). Then it was removed from the heating element and stirred until cooled to room temperature. For
controlling the size of silver nano particles hydroxylamine hydrochloride (ClH4NO) of 5 x 10-3M is added with
different amount like 0.1 ml, 0.2ml, 0.3ml, 0.4ml, 0.5 ml in the original solution. As OH increases then pH
increases as a result it controls the size nano particles. Reaction of Ag nano particle is describe bellow
4Ag+
+ C6H5O7Na3 + 2H2O → 4Ag0
+ C6H5O7H3 + 3Na+
+ H+
+ O2↑
III. RESULT AND DISCUSSION
Size dependent metal nanoparticles are strong scatterers of light at wavelengths near the plasmon
resonance for collective oscillation of the conduction electrons in the metal. For particles with diameters well
below the wavelength of light, a point dipole model describes the absorption and scattering of light well but the
size not less than 50 nm. On scattering different types of theory is introduced like
Mie theory describes the scattering and absorption of electromagnetic radiation by
spherical particles through solving the Maxwell equations. The scattering and absorption cross-sections
are described nicely by Bohren et al. below [19]
1
2
Where, is the polarizability of the particle. Here V is the particle volume, is the dielectric function
of the particle and is the dielectric function of the embedding medium. We can see that when the
particle polarizability will become very large. This is known as the surface plasmon resonance. At the surface
plasmon resonance the scattering cross-section can well exceed the geometrical cross section of the particle. For
example, at resonance a small silver nanoparticle in air has a scattering cross-section that is around ten times the
cross-sectional area of the particle. In such a case, to first-order, a substrate covered with a 10 % areal density of
particles could fully absorb and scatter the incident light. .

3. Silver nanoparticles to enhance the efficiency ……
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200 400 600 800 1000 1200
14
16
18
20
22
24
26
28
Reflectance(%)
Wavelength
After adding Ag Nano particles
Before adding Ag Nano particles
0 1
0
1
Figure 2: Reflectance of Si surface before and after the treatment
It is seen in figure 2 that before depositing nano particle the reflectance was near about 20% but after
depositing the nano particle it is reduces to 15% because when light signed on the top of the solar cell it excite
the silver particle depending on size. The excited nano particle then creates oscillating dipole which causes the
plasmonic effect and it enhance the path length of input light which shown in fig. 4.
200 400 600 800 1000 1200
10
20
30
40
50
60
70
80
90
ExternalQuantumEfficiency
Wavelength (nm)
Before adding Ag Nano particles
After adding Ag Nano particles
0 1
0
1
Figure 3: EQE of Si surface before and after the treatment
Due to the plasmonic effect electron hole pair generation increased which caused the enhancement of
solar cell efficiency. It is seen in figure 3 that the external quantum efficiency is increased after depositing the
silver nano particles that means the electron hole pair generation and collection is increased due to plasmonic
effect.

4. Silver nanoparticles to enhance the efficiency ……
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Figure 4: Plasmonic effect on silver nano particles
IV. CONCLUSION
Path length enhanced in the solar cell due to the properties of silver nanoparticles placed on the top of
the solar cell. Light trapping inside the solar cell is achieved by embedding nanoparticles in the active silicon
layer. The angular scattering from the nanoparticles is enhanced as the mismatch in refractive index with the
embedding medium is maximized. It is also seen that the size of the nanoparticle is also another vital issue as
<50nm size particle reduces the efficiency. In further study by taking different size and shape is investigated.
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