Proceedings of the European Summer School of Photovoltaics 4 – 7 ...

Even greater enhancement was observed for PV cell with
nano-spheres made from pure silver. After two stages of deposition
efficiency increased from 9,8% to 10,6% which means about
7,6% enhancement of efficiency (Table 2). Next attempt of farther
growth of particles density on the surface resulted in drop of efficiency.
Tabl. 2. Solar cells parameters obtained before and after each stage
of 70 nm Ag sphere deposition
Cell number
I sc
[mA]
V oc
[mV]
FF
[%]
E ff
[%]
1-15-50 1040 558 74.7 9.8
1-15-50-02 1093 560 74.4 10.3
1-15-50-03 1097 560 75.8 10.6
1-15-50-04 1075 558 74.7 10.1
Fig. 2. Normalized scattering cross-section for spherical silver nanoparticles
with diameter of 20 nm (blue), 70 nm (green), 100 nm (purple),
200 nm (orange) in medium of refractive index n = 2
This methods are relatively cheap and of wide throughput which
is very important in industrial stage.
Experiment
We used mono crystalline silicon circular shape solar cell with an
area equals to 44 centimeter squared. Nonoparticles source ware
colloidal solutions of 70 nm spheres of Ag and Ag coated with Cu.
Metals concentration in solution was 1080 ppm. Deposition technique
was spin coating. Solution was injecting on wafer spinning
with speed of 4000 rotates per minute. In the first stage 200 µl of
colloidal solution was injected and the same amount in the other
stages. Measurements of cell parameters were taken before and
after deposition of combined Ag-Cu nanoparticles and between
stages of deposition in case of pure Ag spheres. Measurements
were carried out on measuring position equipped with halogen
lamp simulating solar spectrum.
Results and discussion
Theory in this case was confirmed by experimental procedure,
and any time when cell efficiency increased it was connected mainly
with increase of photocurrent as it was expected. For solar cell
without texturisation and antireflection coating (it can be treated
as equivalent of typical thin film cell surface) deposited plasmonic
nanoparticles of Ag-Cu caused increase of efficiency. Results of
I-V measurements are shown in Table 1. In this case overall efficiency
enhancement was about 4.38%.
Tabl. 1. Solar cells parameters obtained before and after Ag-Cu nanoparticles
deposition
Cell number
Isc
[mA]
V oc
[mV]
FF
[%]
E ff
[%]
1-15-42 978 556 71.6 8.8
1-15-42
Ag-Cu
1028 557 70.9 9.2
Where: I sc
– short circuit current, V oc
– open circuit voltage, FF – fill factor,
E ff
– conversion efficiency.
This example of cell response point to conclusion that for any
case exist maximum of particles concentration. Over this concentration
particles begin reflect and absorb more light than is scattered
to the substrate.
For cell with antireflection coating efficiency enhancement was
observed as well, but effect was smaller. Coated and texturised
cell already possess enough reduction of reflection losses that
our method did not work anymore.
Summary
The paper contains:
● broad introduction to the topic of plasmonics for photovoltaic
application,
● the purpose of research was given as well as the description of
one of alternative methods of nanoparticle deposition,
● Addition of plasmonic metal nanospheres resulted in photocurrent
and efficiency enhancement,
● Using of relatively smaller spheres of 70nm diameter and mixtures
of two metals is novel approach. This opens up new are
of research of the best metal mixture.
● Farther studies have to be done to explain explicitly other features
like optimal size and apart between nanoparticles
References
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(2010) 1481–1486.
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[4] Catchpole K., A. Polman, “Plasmonic Solar cell” Optics Express
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