1. Current Solar Cell Technologies and the Application of Nanomaterials
in Photovoltaics
Jennifer Cook
February 11, 2016
Abstract
Worldwide energy usage has increased by approximately 49% over the last 30 years, and the current, total,
global power requirement stands above 1.7 TW.1
At present, the main source of energy conversion, are fossil
fuels, with a larger amount of energy sourced from coal, rather than oil or gas. Technological advances in
nanoscience has opened many doors in the field of renewable energy conversion, particularly for photovoltaic
(PV) devices. Constant progress is being made to improve band gap utilisation, spectral utilisation and
to reduce toxicity. Nanowires and 1D nanoarrays can help to reduce parasitic losses via enhanced light
scattering and increase the amount of incident radiation absorbed into the device. Intermediate band
structures may offer a wider utilisation of the spectrum, with quantum dots offering further efficiency
enhancements. With the ability to tune many properties of nano architectures, as well as control their
size and morphology, it is not only third generation photovoltaics that will benefit from nano-technological
advancements. Current successful applications include the combination of nanoparticles with dyes for use
in dye-sensitised cells, as well as the development of hybrid cells. Nanomaterials hold exciting prospects for
the optimisation of solar power and the future of global energy production, provided the limitations they
pose, can be sufficiently supressed, for them to serve as a more efficient and economically viable option over
current technologies.
1 Introduction
Energy conversion for electricity using renewables in
the UK, has undergone an increase of 550% from the
year 2000 to 2014 as seen in figure 1.2
The graph dis-
plays the main renewable energy sources and the cor-
responding amount of energy produced in each year
in the UK. Increasing interest into photovoltaics as a
viable solution to the energy crisis has led to the pub-
lication of numerous research papers in this field.
Solar cells can be categorised by three generations (Fig-
ure 2).3
Dotted lines are shown with a positive, linear
correlation; in general, the larger the gradient of the
line, the better the solar cell technology, in terms of its
efficiency to cost ratio.
First generation solar cells were based on single crys-
tal or multi-crystalline wafer technologies, and mainly
on single-junctions, therefore possessing a theoretical
conversion efficiency limit, known as the ‘Shockley-
Queisser limit’,4
which stands at approximately 32%
for single junction cells.
Second generation thin-film PV technologies combine
the efforts to improve conversion efficiencies, whilst
maintaining the economic viability of solar cells (Fig-
ure 2). By incorporating nanomaterials into current
PV technologies, efficiency improvements can be made,
even exceeding the Shockley-Queisser limit.
2 P-n Junctions and the Photo-
voltaic cell
Traditional solar cells are based on p-n junction semi-
conductors. As with all p-n junctions, the drift current
is controlled by the density of minority charge carriers.
When light is applied, it acts as a bias voltage to the
junction and the density of the minority charge carri-
ers in each region increases which increases the drift.
When the p/n regions are connected with a conductive
material, a current is produced in the closed circuit.
The electrons flow from the n-region through the cir-
cuit and recombine with a hole in the p-region. If the
circuit is opened, an ‘open circuit voltage’ is produced.
This is known as a photovoltaic cell.5
2.1 Performance of a solar cell
The band structure for a typical semiconductor is shown
in figure 6.3
The band gap energy is directly propor-
tional to the open circuit voltage, and can be increased
by increasing the lifetime τ of the minority charge car-
riers where τ is determined by the recombination rate.
Recombination happens via three main mechanisms:
Shockley Read Hall (SRH),6
Auger7
and Radiative.8
The radiative method is dominant within direct band
gap materials such as GaAs, as additional momentum
does not need to be supplied for recombination. Re-
combination also affects the diffusion length Lp, and as
a rule, the thickness of the solar cell must not exceed
Lp.9
1

2. Figure 1
The graph displays the main renewable energy sources
and the corresponding amount of energy produced in each
year. The largest increase in percentage FiT capacity
from 2013-2014 was from solar photovoltaics (PV), with
an increase of 565MW.
Figure 2
(a) Energy diagram to show the spectral utilisation of
multiple junctions.(b) Spectral splitting mechanism in the
solar cell.
Figure 54
represents excitation within a single junction
cell, where much of the incident light is useless in the
production of charge carriers. The external quantum
efficiency (EQE), measures the ratio of charge carriers
produced from incident light.10
One way of increasing
the EQE, would be to use a multi-junction cell (Figure
2),4
which utilises a wider range of spectral light. In
addition, changing the absorption coefficient α of the
solar cell material can change its absorbency efficiency,
which in turn has an impact on how thick the cell can
be.
2.2 Parasitic Losses
Optical loss mechanisms such as shading and reflection
of light from the cell surface reduce absorption. In ad-
dition, non-active PV layers in anti-reflection coatings
will absorb the light without contributing to charge
carrier generation (parasitic absorption). Another pos-
sible way to reduce reflective losses is to texture the
film (Figure 3).11
Radiation may also be transmitted
through the length of the cell without absorption if the
film is too thin.12
Figure 3
Textured surface of a solar cell, used to increase
absorption via light scattering.
Figure 4
Graphical representation of solar cell efficiency (%) vs cell
cost (US$/ m2
). The oval shaped regions demonstrate how
the three generations of solar cell technology, compare.
3 Thin-film PV technologies
The most promising thin film PV technologies have
shown to be copper indium gallium deselenide (CIGS)
and cadmium telluride (CdTe).13
However, much re-
search is being undertaken to eliminate the amount of
cadmium used in photovoltaics due to its bio-toxicity.14
3.1 CIGS
Copper indium gallium selenide (CIGS) solar cells, have
conversion efficiencies around 20% and are being pro-
duced at the fastest rate among thin film solar cells.
They have high absorption coefficients as they possess
Figure 5
Single junction cell band gap. Not all incident light has
sufficient energy to breach the band gap (qVoc).
2

3. Figure 6
Band structure detailing various loss mechanisms: (1)
Thermal loss, (2) Junction/contact voltage losses,
(4)Recombination loss.
Figure 7
Cross section of a CIGS solar cell, showing the materials
used in each layer and their approximate thicknesses.
a direct band gap structure. Figure 7 shows the cross
section of a typical CIGS cell.15
CIGS may be considered unsustainable, because in-
dium is not an abundant element, presenting a po-
tential limit on their up-scaling. CZTS may offer a
replacement to CIGS in solving this issue, as they are
non-toxic and currently more abundant in availabil-
ity.16
Deb, et al.17
and Kolodinski, et al.18
, have described
an increase in cell efficiency through the creation of
multiple electron-hole pairs upon a single incident pho-
ton.
This is supported by similar work (Figure 8) published
by Semonin, et al.,19
confirming that EQEs above 100%
can be achieved via MEG(Figure 9).20
The intention is
to reduce energy loss via heat, by utilising carriers ex-
cited to higher levels in the conduction band, in order
to generate more electron-hole pairs.
4 Mechanisms
4.1 Down Conversion
The general concept behind down conversion involves
splitting the energy received from energetic photons
into multiple lower energy photons, prior to absorp-
tion into the PV active material.
Nanoparticles prove to be extremely useful when utilis-
Figure 8
Graph of EQE (%) vs Photon Energy (eV), showing the
energies at which the EQE surpassed 100%.
Figure 9
Schematic diagram detailing multiple exciton generation.
An incident photon induces the creation of two e-/h+
pairs (b and c). Non-radiative relaxation follows via
phonon emission (d). The resulting biexciton decays into
single exciton. in this diagram, Franceschetti, et al. have
denoted dissipative processes as dashed arrows and
energy-conserved processes as the solid arrows.
ing this mechanism. In figure 10, van Wijngaarden, et
al.21
have proposed a mechanism for the Pr+3
- Yb+3
couple. The quantised energy of an electron excited
into the conduction band in such nanoparticle systems,
will not be transferred as heat to the lattice. Instead,
the energy is transferred to a neighbouring quantum
dot, which can then excite an electron into the con-
duction band of this neighbouring nanocrystal. Two
different excitons have essentially been produced from
the irradiation of a single, high energy photon.
Now, lower energy photons, produced from the radia-
tive recombination of the QDs, may be absorbed by
the PV material, provided other recombination meth-
ods can be supressed.
Yang, et al.22
, proved that down conversion using quan-
tum dots, can be enhanced even further, by embedding
the QDs into fabricated photonic crystals, which im-
proves the conversion efficiency in contrast to the lone
QDs.
3

4. Figure 10
(a) energy level scheme depicting the simultaneous
transfer of the Y b+
3 ions. (b) Down conversion - the 1G
4
state is used as a bridging level.
Figure 11
Triple-band intermediate cell.
4.2 Intermediate Band Cell
Figure 113
is a schematic representation of a solar cell
with one intermediate band, which helps to utilise a
wider range of incident spectral light. Luque, et al.,23
attempted to increase cell efficiency upon addition of a
third impurity band, and proved that the efficiency ex-
ceeded the Shockley-Quiesser limit both for ideal and
double-tandem cells.
However, the addition of an intermediate level may in-
crease the rate of recombination. This effect is inves-
tigated by Ichimura, et al.24
, where it was duly con-
cluded, that implanting silicon wafers with hydrogen
did not produce significant efficiency improvements.
This suggests that the choice of material when consid-
ering intermediate level addition is also an important
factor.
4.3 Hot Carrier Solar Cell
Energy losses in the form of phonons may be avoided
through the use of a ’hot carrier cell’, appropriately
named for its ability to help eliminate heat losses. Fig-
ure 123
shows how the energy that would traditionally
be lost in a conventional cell, may be stored by a ‘hot
carrier’. In addition, figure 13 shows how the use of
quantum dots in hot carrier cells may also prove ben-
eficial.3
Figure 12
(a) Carriers have reached thermal equilibrium within
the lattice. (b) Hot carrier distribution - carriers can
be held in higher energy states (storing excess
energy).
Figure 13
Simple schematic of the use of quantum dots in hot carrier
solar cells.
5 Dye-sensitised Solar Cells
Dye-sensitised solar cells (DSSC), are based on a photo-
electrochemical system as opposed to a p-n junction.25
They are promising for solar energy conversion, due to
their low production costs and energy-efficient manu-
facturing process, usually favoured when aesthetics are
important.
DSSC’s possess a similar theoretical conversion effi-
ciency of the Si solar cell,26
and are currently the most
efficient27
of the excitonic cells.
Developments have been made regarding the efficiency
and economic viability of DSSCs in recent years. ‘Liq-
uid electrolyte-based dye sensitised solar cells’ have
made advancements through the introduction of TiO2
nanoparticle films used to capture more incident pho-
tons, promoting dye absorption.27
Efficiencies for this
type of DSSC have been improved, by using varying
nanoparticle morphologies as opposed to spherical par-
ticulates, in order to reduce energy losses.28 29
Smooth 1D nano arrays have been seen to possess su-
perior properties over nano-particulates,30
however, do
not have sufficient roughness for dye attachment.31
In-
vestigations have been undertaken, to raise the rough-
ness factor of the nanoarrays. Varghese, et al.32
de-
posited titanium films onto fluorine-doped glass sub-
4

5. Figure 14
Results from investigation by Standridge, et al., showing
the IPCE (%) vs irradiation wavelength (nm).
strates and noted that the fill factor for DSSCs was
approximatelt 25% lower than the nanoparticle counter
parts. The group suggested that this occurred due to
an increase in width at the TNO-FTO interface and
that by increasing the nanotube roughness factor, this
problem could be resolved and greater efficiencies could
be achieved. Liao, et al.33
confirmed this hypothe-
sis, by proving that an increase in surface roughness
of TiO2 nano architectures, will create surfaces more
adapt for sunlight harvesting and dye absorption.
Standridge, et al.34
showed that the combination of sil-
ver nanoparticles and dye, promoted the production of
more electrons than in TiO2 or the dye alone. Figure
14 displays part of the group’s results, which clearly
show that at almost all wavelengths, the incident pho-
ton conversion efficiency (IPCE) is higher with the NP-
Dye combination.
Controlling the plasmonic frequency of nanoparticles
for efficiency optimisation, has proven to be a difficult
task. However, groups have discovered that variation
in nano architecture morphology, does shift the plas-
mon frequency and boost the IPCE in DSSCs.35 36
There is no doubt on the success in the enhancement
of DSSCs through the use of nanostructured materi-
als, however currently, their economic viability is not
promising, due to the complex methods involved in
their syntheses.3 37
6 Polymer-hybrid Cells
Polymer-hybrid cells offer easier manufacture, in com-
bination with high absorption coefficients, typical of
polymers (105
cm−1
).38
They offer large scale solar en-
ergy conversion with thin cells at lower costs.
The disadvantage, however, being that PV devices con-
taining polymers tend to possess poor charge trans-
port,39
suggesting that if maximum efficiencies are re-
Figure 15
Scanning electron microscopy (SEM) images of different
nanowire arrays; (a) Si, (b) ZnO, (c) InGaN.
quired, nanowire arrays may be ideal.40
7 Semiconductor Nanowires and
Nano architectures
Nanowires can be identified as long flexible rods with a
diameter in the range 1 – 100 nm as seen in figure 15.41
In contrast to the bulk, the nanoscale materials have
promising prospects for higher efficiency photovoltaic
devices.
Conventional silicon wafers often have to be thick to
absorb enough light, adding to the recombination rate.
Nanowires may offer a solution to this problem by re-
ducing the diffusion length of the minority charge car-
riers. Kato, et al.42
investigated surface passivation
techniques on nanowires and discovered that atomic
layer deposition (ALD) did increase the lifetime of the
charge carriers. Nanowire diameters also affect resis-
tance43
suggesting a change in the occupied volume by
conduction carriers.
Studies based on Si-nanowire PV applications, reveal
that longer nanowires enhance the absorption and ge-
ometry based on nanowire arrays provide more efficient
light scattering, in comparison to thin films.44
Fang, et
al. discovered that although ’slantingly-aligned’ nanowire
arrays are superior to the original vertical alignment,
they are still limited by a high rates of surface recom-
bination.45
Numerous groups have undertaken research on the P3HT
- ZnO nanowire arrays. Greene et.al46
significantly
increased efficiencies through the addition of polycrys-
talline TiO2 with confirmation of this result from Plank
5

6. et.al47
through the incorporation of an MgO shell.
8 Conclusion
Many aspects of solar technologies currently on the
market have been discussed, as well as the importance
of developing innovative new materials, to keep up with
the ever increasing demand for energy and the ongoing
quest to reduce environmental impacts.
It is evident that there are countless applications for
the incorporation of nanomaterials into PV devices,
ranging from technologies modelled purely around nano-
materials to small additions such as quantum dots or
nanoparticle-dye mixtures. If researchers can sufficiently
suppress the current limitations, that some advanced
concepts pose, nanomaterials really could be the key
to efficient, sustainable energy. There is no doubt that
the future is bright for solar energy.
References
1. I. E. Agency, Key World Energy Statistics. 2014.
2. Gov.uk, Digest of UK Energy Statistics (DUKES).
2014.
3. M. A. Green, “Third generation photovoltaics:
Ultra-high conversion efficiency at low cost,” Prog.
Photovolt: Res. Appl., vol. 9, no. 2, pp. 123–135,
2001.
4. A. Polman and H. A. Atwater, “Photonic design
principles for ultrahigh-efficiency photovoltaics,”
Nature Materials, vol. 11, no. 3, pp. 174–177, 2012.
5. C. D. Mickey, “Solar photovoltaic cells,” J. Chem.
Educ., vol. 58, no. 5, p. 418, 1981.
6. W. Shockley and W. T. Read, “Statistics of the
recombinations of holes and electrons,” Phys. Rev.,
vol. 87, no. 5, pp. 835–842, 1952.
7. A. Haug and W. Ekardt, “The influence of screen-
ing effects on the auger recombination in semi-
conductors,” Solid State Communications, vol. 17,
no. 3, pp. 267–268, 1975.
8. J. R. Barker, “Radiative recombination in the
electronic ground state,” The Journal of Physical
Chemistry, vol. 96, no. 18, pp. 7361–7367, 1992.
9. S. Beeby and N. White, Energy harvesting for au-
tonomous systems. Artech House, 2010.
10. J. Halme, G. Boschloo, A. Hagfeldt, and P. Lund,
“Spectral characteristics of light harvesting, elec-
tron injection, and steady-state charge collection
in pressed tio 2 dye solar cells,” J. Phys. Chem. C,
vol. 112, no. 14, pp. 5623–5637, 2008.
11. M. Ratner, “The physics of solar cells; third gen-
eration photovoltaics: Advanced solar energy con-
version,” Phys. Today, vol. 57, no. 12, pp. 71–72,
2004.
12. M. Tao, Terawatt solar photovoltaics. Springer.
13. M.-J. C. C.-Y. W. M. X. Jiang Liu, Da-
Ming Zhuang and X.-L. Li, “Preparation and char-
acterisation of cu(in,ga)se2 thin films by seleniza-
tion of cu0.8ga0.2 and in2se3 precursor films,”
International Journal of Photoenergy, vol. 2012,
pp. 1–7, 2012.
14. A. Sigel, H. Sigel, and R. K. O. Sigel, Cadmium.
Springer, 2013.
15. U. P. Singh and S. P. Patra, “Progress in polycrys-
talline thin-film cu(in,ga)se2 solar cells,” Interna-
tional Journal of Photoenergy, vol. 2012, pp. 1–19,
2010.
16. C. Wadia, A. P. Alivisatos, and D. M. Kammen,
“Materials availability expands the opportunity
for large-scale photovoltaics deployment,” Envi-
ronmental Science and Technology, vol. 43, no. 6,
pp. 2072–2077, 2009.
17. S. Deb and H. Saha, “Secondary ionisation and its
possible bearing on the performance of a solar cell,”
Solid-State Electronics, vol. 15, no. 12, pp. 1389–
1391, 1972.
18. S. Kolodinski, J. H. Werner, T. Wittchen, and H. J.
Queisser, “Quantum efficiencies exceeding unity
due to impact ionization in silicon solar cells,”
Appl. Phys. Lett., vol. 63, no. 17, p. 2405, 1993.
19. O. E. Semonin, J. M. Luther, S. Choi, H.-Y. Chen,
J. Gao, A. J. Nozik, and M. C. Beard, “Peak ex-
ternal photocurrent quantum efficiency exceeding
100via meg in a quantum dot solar cell,” Science,
vol. 334, no. 6062, pp. 1530–1533, 2011.
20. A. Franceschetti, J. M. An, and A. Zunger, “Im-
pact ionization can explain carrier multiplication in
pbse quantum dots,” Nano Letters, vol. 6, no. 10,
pp. 2191–2195, 2006.
21. J. T. van Wijngaarden, S. Scheidelaar, T. J. H.
Vlugt, M. F. Reid, and A. Meijerink, “Energy
transfer mechanism for downconversion in the ( pr
3 + , yb 3 + ) couple,” Phys. Rev. B, vol. 81,
no. 15, 2010.
22. F. Yang and B. T. Cunningham, “Enhanced quan-
tum dot optical down-conversion using asymmetric
2d photonic crystals,” Opt. Express, vol. 19, no. 5,
p. 3908, 2011.
23. A. Luque and A. Marta, “Increasing the efficiency
of ideal solar cells by photon induced transitions
at intermediate levels,” Phys. Rev. Lett., vol. 78,
no. 26, pp. 5014–5017, 1997.
6

7. 24. M. Ichimura, H. Sakakibara, K. Wada, and
M. Kato, “Efficiency of a solar cell with intermedi-
ate energy levels: An example study on hydrogen
implanted si solar cells,” J. Appl. Phys., vol. 114,
no. 11, p. 114505, 2013.
25. M. Gratzel, “Photoelectrochemical cells,” Nature,
vol. 414, pp. 338–344, 2001.
26. H. J. Snaith, “Estimating the maximum attainable
efficiency in dye-sensitized solar cells,” Adv. Funct.
Mater., vol. 20, no. 1, pp. 13–19, 2010.
27. H. S. Jung and J.-K. Lee, “Dye sensitized solar cells
for economically viable photovoltaic systems,” J.
Phys. Chem. Lett., vol. 4, no. 10, pp. 1682–1693,
2013.
28. M. Law, L. E. Greene, J. C. Johnson, R. Saykally,
and P. Yang, “Nanowire dye-sensitized solar cells,”
Nature Materials, vol. 4, no. 6, pp. 455–459, 2005.
29. M. Yang, B. Ding, S. Lee, and J.-K. Lee, “Carrier
transport in dye-sensitized solar cells using single
crystalline tio 2 nanorods grown by a microwave-
assisted hydrothermal reaction,” J. Phys. Chem.
C, vol. 115, no. 30, pp. 14534–14541, 2011.
30. W.-Q. Wu, B.-X. Lei, H.-S. Rao, Y.-F. Xu, Y.-F.
Wang, C.-Y. Su, and D.-B. Kuang, “Hydrothermal
fabrication of hierarchically anatase tio2 nanowire
arrays on fto glass for dye-sensitized solar cells,”
Sci. Rep., vol. 3, 2013.
31. E. Ghadiri, N. Taghavinia, S. M. Zakeeruddin,
M. Gratzel, and J.-E. Moser, “Enhanced electron
collection efficiency in dye-sensitized solar cells
based on nanostructured tio 2 hollow fibers,” Nano
Letters, vol. 10, no. 5, pp. 1632–1638, 2010.
32. O. K. Varghese, M. Paulose, and C. A. Grimes,
“Long vertically aligned titania nanotubes on
transparent conducting oxide for highly efficient
solar cells,” Nature Nanotech, vol. 4, no. 9,
pp. 592–597, 2009.
33. J.-Y. Liao, B.-X. Lei, H.-Y. Chen, D.-B. Kuang,
and C.-Y. Su, “Oriented hierarchical single crys-
talline anatase tio2 nanowire arrays on ti-foil
substrate for efficient flexible dye-sensitized solar
cells,” Energy Environ. Sci., vol. 5, no. 2, pp. 5750–
5757, 2012.
34. S. D. Standridge, G. C. Schatz, and J. T. Hupp,
“Distance dependence of plasmon-enhanced pho-
tocurrent in dye-sensitized solar cells,” J. Am.
Chem. Soc., vol. 131, no. 24, pp. 8407–8409, 2009.
35. B. Ding, B. J. Lee, M. Yang, H. S. Jung, and J.-
K. Lee, “Surface-plasmon assisted energy conver-
sion in dye-sensitized solar cells,” Advanced Energy
Materials, vol. 1, no. 3, pp. 415–421, 2011.
36. L. Q. X. X.-W. K. W.-C. T. Chang, S., “En-
hancement of low energy sunlight harvesting in
dye-sensitized solar cells using plasmonic gold
nanorods,” Energy Environ. Sci, vol. 5, pp. 9444–
9448, 2012.
37. J. B. Baxter, “Commercialization of dye-sensitized
solar cells: Present status and future, research
needs to improve efficiency, stability, and manufac-
turing,” J. Vac. Sci. Technol. A, vol. 30, pp. 9444–
9448, 2012.
38. S. E. Gledhill, B. Scott, and B. A. Gregg, “Organic
and nano-structured composite photovoltaics: An
overview,” Journal of Materials Research, vol. 20,
no. 12, pp. 3167–3179, 2005.
39. N. C. Greenham, X. Peng, and A. P. Alivisatos,
“Charge separation and transport in conjugated-
polymer semiconductor-nanocrystal composites
studied by photoluminescence quenching and pho-
toconductivity,” Phys. Rev. B, vol. 54, no. 24,
pp. 17628–17637, 1996.
40. B. Kannan, K. Castelino, and A. Majumdar,
“Design of nanostructured heterojunction polymer
photovoltaic devices,” Nano Letters, vol. 3, no. 12,
pp. 1729–1733, 2003.
41. A. I. Hochbaum and P. Yang, “Semiconductor
nanowires for energy conversion,” Chemical Re-
views, vol. 110, no. 1, pp. 527–546, 2010.
42. S. Kato, Y. Kurokawa, S. Miyajima, Y. Watan-
abe, A. Yamada, Y. Ohta, Y. Niwa, and M. Hi-
rota, “Improvement of carrier diffusion length in
silicon nanowire arrays using atomic layer depo-
sition,” Nanoscale Res Lett, vol. 8, no. 1, p. 361,
2013.
43. Y.-J. Doh, S. D. Franceschi, E. P. A. M. Bakkers,
and L. P. Kouwenhoven, “Andreev reflection ver-
sus coulomb blockade in hybrid semiconductor
nanowire devices,” Nano Letters, vol. 8, no. 12,
pp. 4098–4102, 2008.
44. L. Hu and G. Chen, “Analysis of optical absorption
in silicon nanowire arrays for photovoltaic applica-
tions,” Nano Letters, vol. 7, no. 11, pp. 3249–3252,
2007.
45. H. Fang, X. Li, S. Song, Y. Xu, and J. Zhu, “Fab-
rication of slantingly-aligned silicon nanowire ar-
rays for solar cell applications,” Nanotechnology,
vol. 19, no. 25, p. 255703, 2008.
46. L. E. Greene, M. Law, B. D. Yuhas, and P. Yang,
“Zno-tio2 core-shell nanorod/p3ht solar cells,” The
Journal of Physical Chemistry, vol. 111, pp. 18451–
18456, 2007.
47. N. O. V. Plank, H. J. Snaith, C. Ducati, J. S.
Bendall, L. Schmidt-Mende, and M. E. Welland,
“A simple low temperature synthesis route for
zno-mgo core-shell nanowires,” Nanotechnology,
vol. 19, no. 46, p. 465603, 2008.
7