Zinc oxide-zinc stannate core-shell nanorod arrays for CdS quantum dot sensitized solar cells

Article abstract of DOI:10.1016/j.electacta.2012.02.036

Nanorod arrays of zinc oxide-zinc stannate core-shell photoelectrodes were prepared by a simple hydrothermal process and cadmium sulfide (CdS) quantum dot sensitized solar cells were fabricated. The photocurrent density of the core-shell photoelectrode was found to improve by ～2.4 times compared to ZnO nanorod photoelectrodes, due to improved surface area and charge transport in the core-shell photoelectrodes. With a thin layer of ZnS on the CdS quantum dot surface, the core-shell quantum dot sensitized solar cell demonstrated maximum power conversion efficiency of 1.24% under 1 sun illumination (AM1.5).

Full text of DOI:10.1016/j.electacta.2012.02.036

Electrochimica Acta 68 (2012) 141–145
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Electrochimica Acta
journal homepage: www.elsevier.com/locate/electacta
Zinc oxide–zinc stannate core–shell nanorod arrays for CdS quantum dot
sensitized solar cells
Tanujjal Bora, Htet H. Kyaw, Joydeep Dutta∗
Center of Excellence in Nanotechnology, Asian Institute of Technology, P.O. Box 4, Klong Luang, Pathumthani 12120, Thailand
a r t i c l e i n f o
a b s t r a c t
Article history:
Received 28 August 2011
Received in revised form 10 February 2012
Accepted 10 February 2012
Available online 19 February 2012
Nanorod arrays of zinc oxide–zinc stannate core–shell photoelectrodes were prepared by a simple
hydrothermal process and cadmium sulfide (CdS) quantum dot sensitized solar cells were fabricated. The
photocurrent density of the core–shell photoelectrode was found to improve by ∼2.4 times compared
to ZnO nanorod photoelectrodes, due to improved surface area and charge transport in the core–shell
photoelectrodes. With a thin layer of ZnS on the CdS quantum dot surface, the core–shell quantum dot sen-
sitized solar cell demonstrated maximum power conversion efficiency of 1.24% under 1 sun illumination
(AM1.5).
Keywords:
Zinc stannate
Zinc oxide nanorod
Core–shell nanorod
Cadmium sulfide
© 2012 Elsevier Ltd. All rights reserved.
Quantum dot sensitized solar cell
1. Introduction
or nanorods, would provide a direct pathway for electron trans-
port reducing the probability of electron hopping observed in solar
Quantum dot sensitized solar cells (QDSSCs) are gaining
renewed attention due to the simple structure and low cost man-
ufacturing possibilities. Semiconductor quantum dots (QDs) light
harvesting elements can replace organic dyes in a typical dye sen-
sitized solar cell structure as it has a higher absorption coefficient
compared to organic dye molecules [1], long-term photostability
[2], tunable size-bandgap property [3], multiple exciton generation
capability through impact ionization [4], etc. which has poten-
tial to boost QD solar cell power conversion efficiencies higher
than the conventional silicon based solar cells commercially avail-
able today [4,5]. Among the various semiconductor QDs used in
QDSSCs, cadmium sulfide (CdS) is one of the most widely used
material due to its bulk bandgap of 2.42 eV and direct bandgap
absorption characteristics. Several reports on CdS QDSSCs mostly
using titanium dioxide (TiO2) as photoelectrode material have
been reported till date [6–8]. Zinc oxide (ZnO) is one of the most
extensively studied materials as an alternative to TiO2, since it
has a direct bandgap (3.37 eV), higher exciton energy (60 m eV)
[9], higher electron mobility (200 cm2 V−1 s−1) [10] and can be
grown in various shapes with relative ease [11]. In addition, appli-
cation of one dimensional nanostructures of ZnO, like nanowires
cells constructed with nanoparticulate porous thin films that leads
to an improvement in the charge transfer mechanism by several
orders of magnitude [12]. However, the maximum reported power
conversion efficiency (PCE) of CdS QDSSC using ZnO nanorods as
photoelectrode material is still relatively low (0.54%) [13] due to
lower photoelectrode surface area and high interfacial electron
recombination at the ZnO/electrolyte interface.
In the quest for a better material for photoelectrochemical cells,
ternary oxides are one of the most promising materials due to
their tunable chemical and physical properties, mainly controlled
by the composition of the material. Burnside et al. [14] has reported
the use of strontium titanate (SrTiO3) as photoelectrode mate-
rial for DSSC and demonstrated higher photovoltage compared to
typical TiO2 based DSSCs. Similarly, Tan et al. [15] has reported
zinc stannate (Zn2SnO4) as photoelectrode material with a DSSC
efficiency of 3.8% under 1 sun illumination. Zinc stannate is an
n-type ternary oxide of zinc and tin with two crystallographic struc-
tures: metastannate Perovskite ZnSnO3 (bandgap ∼3.40 eV) and
orthostannate cubic spinal Zn2SnO4 (bandgap ∼3.60 eV). Because
of the high electrical conductivity and low visible light absorption,
Zn2SnO4 is a good candidate for applications in transparent con-
ducting thin films [16], solar cells [15,17], photocatalysis [18,19],
gas sensors [20,21], anode material for Li-ion battery [22], etc. In
addition, higher chemical stability of Zn2SnO4 in wide range of pH
makes it a suitable photoelectrode material, though very few stud-
ies have been reported till date on Zn2SnO4 applications in solar
cells.
∗
Corresponding author. Current address: Nanotechnology, Water Research
Center, Sultan Qaboos University, P.O. Box 50, Postal Code 123, Al Khoudh, Oman.
Tel.: +96 8 2441 3266/+66 2 524 5680; fax: +96 8 2441 3532/+66 2 524 5617.
E-mail addresses: joy@ait.asia, dutta@squ.edu.om (J. Dutta).
0013-4686/$ – see front matter © 2012 Elsevier Ltd. All rights reserved.
doi:10.1016/j.electacta.2012.02.036

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T. Bora et al. / Electrochimica Acta 68 (2012) 141–145
In this work, we report the use of ZnO–Zn2SnO4 core–shell
rinsed with DI water–methanol cosolvent for another 1 min. These
four steps are termed as 1 SILAR deposition cycle and similar cycles
were repeated several times in order to grow sufficient amount of
CdS QDs on the photoelectrodes. The entire deposition process was
carried out at room temperature. Finally, the CdS QD coated photo-
electrodes were rinsed thoroughly with DI water and allowed to dry
at room temperature in a dehumidifying chamber (WEIFO DRY60,
RH < 30%).
nanorod arrays as photoelectrode material to enhance the per-
formance of CdS QDSSC. Recently, Li et al. [23] has reported the
use of Zn2SnO4 for CdS QDSSC with power conversion efficiency
of 0.228%. The lower PCE was attributed to the lower electron
mobility (∼21 cm2 V−1 s−1) [16] and shorter diffusion length [15] in
Zn2SnO4 compared to ZnO. In this present study, we demonstrate
the improved performance of CdS QDSSC with hydrothermally
grown ZnO–Zn2SnO4 core–shell photoelectrodes by overcoming
the problem of lower electron mobility as well as shorter diffusion
length of Zn2SnO4 by allowing the charge transfer in the device to
occur through the ZnO core. Accordingly, the core–shell photoelec-
trode, which has also demonstrated higher surface area than the
bare ZnO nanorod photoelectrode, increased the photocurrent and
photovoltage of the CdS QDSSC resulting in a fourfold improvement
in the power conversion efficiency.
A
thin layer of zinc sulfide (ZnS) was deposited on
some of the CdS QDs by similar SILAR process where the
25 mM Cd(CH3COO)2·2H2O solution was replaced by 25 mM
Zn(CH3COO)2·2H2O solution. Dipping and rinsing times were kept
constant at 1 min and 3 SILAR deposition cycles were carried out to
form the ZnS layer.
In order to study the annealing effect on the CdS QDSSC, some
of the CdS QD deposited ZnO–Zn2SnO4 core–shell photoelectrodes
were annealed at different temperatures up to 250 ◦C. Annealing
was carried out in nitrogen atmosphere in order to reduce further
oxidation of the CdS QDs.
2. Experimental details
All chemicals used in this study were analytical grade and
used without further purification. Fluorine doped tin oxide (FTO)
conducting glass substrates acquired from Asahi Glass Company,
Japan were cleaned by successive sonication with soap water, ace-
tone, ethanol and DI water for 15 min each. For the synthesis of
ZnO–Zn2SnO4 core–shell nanorod arrays, zinc acetate dihydrate
(Zn(CH3COO)2·2H2O), zinc nitrate hexahydrate (Zn(NO3)2·6H2O),
hexamethylenetetramine (C6H12N4), tin chloride pentahydrate
(SnCl4·5H2O) and sodium hydroxide (NaOH) were used as start-
ing materials. Cadmium acetate (Cd(CH3COO)2·2H2O) and sodium
sulfide (Na2S) were used as Cd2+ and S2− sources for the synthesis
of CdS quantum dots.
2.3. Fabrication of the CdS quantum dot sensitized solar cells
For the CdS QDSSC, a platinum (Pt) coated FTO substrate as
counter electrode was placed on top of the CdS QD deposited bare
ZnO or ZnO–Zn2SnO4 core–shell nanorod photoelectrodes and a
50 ␮m thick layer of surlyn 1702 (DuPont) was placed in between
the two electrodes as spacer. Thin film of Pt catalyst was deposited
on the counter electrode by thermal decomposition of 5 mM hex-
achloroplatinic acid (H2PtCl6·6H2O) in isopropanol at 385 ◦C for
30 min. The two electrodes were then sealed and the inter electrode
space was filled with a polysulfide electrolyte composed of 0.5 M
Na2S, 2 M S and 0.2 M KCl in 3:7 volume ratio of DI water–methanol
cosolvent. The active area of all the CdS QDSSCs was kept constant
at 0.25 cm2.
2.1. Synthesis of ZnO–Zn2SnO4 core–shell nanorod array
ZnO–Zn2SnO4 core–shell nanorod arrays were synthesized by
a two step hydrothermal process. First, vertically aligned ZnO
nanorods arrays were grown on FTO substrates as reported in our
previous reports [24–26]. Briefly, ZnO nanoparticle seeded FTO
substrates were dipped in an aqueous precursor solution (100 ml)
containing 20 mM Zn(NO3)2·6H2O and 20 mM C6H12N4 and the
reaction bath was sealed. The growth of the ZnO nanorods was car-
ried out at 95 ◦C for 40 h. The FTO substrates containing the ZnO
nanorods were then rinsed thoroughly with deionized (DI) water
and annealed at 250 ◦C in air for 1 h in order to remove any organic
molecules present on the surface of the nanorods.
For the deposition of the Zn2SnO4 shell layer, as prepared
ZnO nanorod arrays were dipped in a 50 ml aqueous solution of
SnCl4·5H2O (5 mM) and NaOH (50 mM) with 1:10 molar ratio and
the reaction bath was placed in an autoclave at 120 ◦C for 2 h, after
which the autoclave was allowed to cool down to room tempera-
ture. The substrates were then rinsed with DI water, followed by
annealing at 450 ◦C for 1 h in the ambient.
2.4. Characterization
Structural characterization of ZnO–Zn2SnO4 core–shell
nanorods was performed with X-ray diffraction technique (XRD,
JEOL JDX-3530 with Cu K␣ radiation) and the morphology of these
structures were studied by transmission electron microscopy (TEM,
JEOL JEM-2010) and scanning electron microscopy (SEM, JEOL
JSM-6301F) operating at 200 kV and 20 kV respectively. Optical
absorptions were measured by using a UV-Vis spectrophotometer
from Ocean Optics (Micropack DH-2000). Current–voltage (J–V)
characteristics of the CdS QDSSCs were measured at calibrated 1
sun illumination (AM 1.5, 100 mW/cm2) by using a SF150 small
beam solar simulator from Sciencetech as light source with a
programmable electrometer (Keithley 617) as a voltage source.
3. Results and discussion
XRD patterns of the ZnO–Zn2SnO4 core–shell photoelectrodes
are shown in Fig. 1. Before annealing the core–shell photoelec-
trodes at 450 ◦C, the shell layer was identified as mixed phase of the
metastable zinc hydroxystannate [ZnSn(OH)6] and zinc stannate
(Zn2SnO4), confirmed from standard data file JCPDS 20-1455 and
JCPDS 24-1470 respectively. After annealing in air at 450 ◦C for 1 h,
the XRD peaks from the ZnSn(OH)6 phase were observed to disap-
pear and only peaks from thermodynamically stable Zn2SnO4 were
observed, indicating transformation of the metastable ZnSn(OH)6
to Zn2SnO4 (Fig. 1(b)). We have also observed that some of the XRD
peaks from the shell layer were suppressed by or overlapped by the
strong diffractions from ZnO core, due to the presence of relatively
higher amount of ZnO (more than 90%) compared to ZnSn(OH)6 or
Zn2SnO4 phases in the core–shell photoelectrodes.
2.2. In situ growth of CdS quantum dots on photoelectrode
CdS quantum dots were deposited on the surface of bare ZnO
nanorods and ZnO–Zn2SnO4 core–shell nanorod arrays by succes-
sive ionic layer adsorption and reaction (SILAR) process. A 25 mM
Cd(CH3COO)2·2H2O solution (solution A) in DI water–ethanol
cosolvent (3:7 vol. ratio) was used as the source for the Cd2+
ions and a separate 25 mM Na2S solution (solution B) in DI
water–methanol cosolvent (3:7 vol. ratio) was used as S2− source.
In
a typical deposition process, the bare ZnO nanorod and
ZnO–Zn2SnO4 core–shell nanorod samples were first dipped in the
solution A for 1 min, then rinsed with DI water–ethanol cosolvent
for 1 min, followed by dipping in the solution B for 1 min and finally

T. Bora et al. / Electrochimica Acta 68 (2012) 141–145
143
Fig. 2. (a) SEM images of ZnO–Zn2SnO4 core–shell and bare ZnO (inset) nanorod
arrays hydrothermally grown on conducting FTO substrate, (b) low resolution TEM
image of one single ZnO–Zn2SnO4 core–shell nanorod, (c) magnified TEM image of
the ZnO–Zn2SnO4 core–shell nanorod showing the (3 1 1) crystal plane of Zn2SnO4
corresponding to d-spacing 0.26 nm is found at the surface and (d) TEM image of
CdS quantum dots deposited on the surface of a typical ZnO–Zn2SnO4 core–shell
nanorod.
Fig. 1. XRD patterns of the core–shell photoelectrodes (a) before and (b) after
annealing at 450 ◦C for 1 h in air. The (h k l) planes representing ZnSn(OH)6 and
Zn2SnO4 are marked with (•) and (*) respectively and the unmarked peaks cor-
respond to the ZnO nanorod core.
nanorod (Fig. 2(c)) was found to be 0.26 nm corresponding to the d-
spacing of the (3 1 1) plane of Zn2SnO4, indicating the crystal plane
is exposed at the surface of the core–shell nanorod. The presence of
the Zn2SnO4 in the core–shell nanorod array was confirmed from
the XRD results (Fig. 1(b)) and from the TEM images. From the SEM,
complete coverage of the ZnO nanorods surface by Zn2SnO4 layer
are observed, which rules out the presence of the (0 0 2) plane of
ZnO at the surface of the core–shell structure whose d-spacing also
is 0.26 nm. Fig. 2(d) shows a low resolution TEM image of CdS quan-
tum dots deposited in situ on the surface of a single ZnO–Zn2SnO4
core–shell nanorod.
The ZnO–Zn2SnO4 core–shell nanorod arrays were then used as
working electrodes to fabricate CdS QDSSCs. Fig. 3 shows the opti-
cal absorption spectra of CdS quantum dot sensitized ZnO–Zn2SnO4
core–shell photoelectrodes. It was found that with increasing num-
ber of SILAR cycles, the optical response of the CdS quantum dot
anchored core–shell photoelectrode increases in the visible region.
For 15 SILAR deposition cycles, maximum absorption in the vis-
ible region (increasing about threefold at 400 nm) was obtained
for the CdS quantum dot sensitized core–shell photoelectrode. For
the higher number of deposition cycles, reduction in the visible
light absorption of the photoelectrodes was observed due to the
detachment of some of the deposited CdS quantum dots from the
photoelectrode surfaces.
Fig. 2(a) shows the SEM image of the ZnO–Zn2SnO4 core–shell
nanorod arrays, where it can be observed that following the growth
of the Zn2SnO4 layer, the surface area of the core–shell photoelec-
trode increases compared to the bare ZnO nanorod arrays (inset in
Fig. 2(a)). The increase in the surface area of the core–shell photo-
electrode was then calculated in terms of roughness factor of the
photoelectrodes (see in the supporting information) as is shown
in Table 1. In case of the ZnO–Zn2SnO4 core–shell photoelectrode,
∼23% enhancement in the roughness factor was observed com-
pared to the bare ZnO nanorod photoelectrode.
Fig. 2(b) shows a low resolution TEM image of a single
ZnO–Zn2SnO4 core–shell nanorod showing a rough surface of uni-
form coating of the Zn2SnO4 on a typical ZnO nanorod core. The
distance between two adjacent crystal planes at the surface of the
Table 1
Roughness factor of bare ZnO and ZnO–Zn2SnO4 core–shell nanorod
photoelectrodes.a
Photoelectrodes
Roughness factor
Bare ZnO nanorod
ZnO–Zn2SnO4 core–shell
6.50 × 102
8.01 × 102
The J–V characteristics of the CdS quantum dot sensitized bare
ZnO and ZnO–Zn2SnO4 core–shell nanorod solar cells with increas-
ing number of deposition cycles are shown in Table 2. Short circuit
a
The photoelectrode substrate area used to calculate the roughness factor was
0.5 cm2.

144
T. Bora et al. / Electrochimica Acta 68 (2012) 141–145
Table 2
J–V characteristics of the CdS quantum dot sensitized solar cells with bare ZnO and ZnO–Zn2SnO4 core–shell nanorods as working electrodes, measured at 1 sun illumination
(AM1.5, 100 mW/cm2).
No. of SILAR cycles
Bare ZnO nanorod
ZnO–Zn2SnO4 core–shell nanorod
Voc (V)
Jsc (mA/cm2)
FF (%)
Á (%)
Voc (V)
Jsc (mA/cm2)
FF (%)
Á (%)
5
10
15
20
25
0.14
0.30
0.61
0.68
0.68
0.25
0.82
1.14
1.30
1.20
25.96
30.09
28.14
28.66
27.06
0.01
0.07
0.20
0.25
0.22
0.37
0.48
0.68
0.71
0.71
1.54
2.04
2.79
3.10
3.07
33.17
33.87
38.02
41.81
39.85
0.19
0.33
0.72
0.92
0.87
current density (Jsc) for both bare ZnO and ZnO–Zn2SnO4 core–shell
nanorod photoelectrode was observed to increase with increasing
amount of CdS quantum dots, which is in good agreement with
the increasing optical absorptions of the CdS sensitized photo-
electrodes shown in Fig. 3. Compared to the bare ZnO nanorod,
improved performance of the ZnO–Zn2SnO4 core–shell CdS QDSSC
was observed. Optimum Jsc (3.10 mA/cm2) was obtained for 20
SILAR cycles, after which a slight reduction in Jsc was observed in
solar cells fabricated with increasing number of SILAR cycles due
to the detachment of the quantum dots from the photoelectrode
surfaces as explained earlier. The enhanced photocurrent observed
in case of the core–shell photoelectrode can thus be attributed to
the higher surface area of the core–shell photoelectrode as shown
in Table 1 and also due to the improved charge separation at
the core–shell photoelectrode leading to lower interfacial charge
recombination compared to the bare ZnO nanorod photoelectrodes.
The energy band diagram of the ZnO–Zn2SnO4 core–shell CdS
QDSSC showing the possible electron transfer path is given in Fig. 4.
The presence of the higher bandgap Zn2SnO4 (3.60 eV) shell on the
ZnO (3.37 eV) core, allows the photoexcited electrons to transfer
from the conduction band (CB) of CdS to the CB of Zn2SnO4, which
then subsequently transfers to the CB of ZnO that is just below the
CB of Zn2SnO4. The final electron diffusion takes place through the
ZnO core which lowers the probability of interfacial recombination
of the electrons by keeping them away from the semiconduc-
tor/QD or semiconductor/electrolyte interface. This leads to an
improvement of the charge separation at the core–shell photoelec-
trode resulting in a higher electron density in the photoelectrodes.
As a consequence, a large improvement in the fill factor (FF)
was observed in case of the ZnO–Zn2SnO4 core–shell CdS QDSSC
(41.81%) compared to the bare ZnO nanorod CdS QDSSC (28.66%).
The open circuit voltage (Voc) was also observed to improve slightly
from 0.68 V to 0.71 V due to the higher electron density in the
core–shell photoelectrode compared to the bare ZnO nanorod
photoelectrode. The optimum performance of the ZnO–Zn2SnO4
core–shell CdS QDSSC was achieved for 20 SILAR deposition cycles,
which yielded maximum power conversion efficiency (PCE) of
0.92% (Voc = 0.71 V, Jsc = 3.10 mA/cm2 and FF = 41.81%) under 1 sun
illumination.
In order to improve the performance of the ZnO–Zn2SnO4
core–shell CdS QDSSC, annealing of the CdS QD deposited
core–shell photoelectrodes was then carried out. It is well docu-
mented that annealing process could improve the crystallinity of
the QDs by reducing the defect states in QDs and could improve the
electron transport property in the QD film as well as in the photo-
electrode [27–30]. Recently Song et al. [31] has shown a significant
efficiency enhancement in the QDSSC (from 0.05% to 0.73%) after
annealing the QD deposited ZnO nanorod photoelectrodes. Simi-
larly, with annealed lead sulfide (PbS) quantum dots, Zhao et al.
[32] has demonstrated a very high fill factor (∼62%) which can be
mainly attributed to the improved charge transport in the annealed
QD film. In the present study, the CdS QD sensitized ZnO–Zn2SnO4
core–shell photoelectrodes were annealed in N2 atmosphere for
1 h in order to avoid the oxidation of the QDs. Table 3 shows the
J–V characteristics of the annealed ZnO–Zn2SnO4 core–shell CdS
QDSSCs. A significant enhancement of the core–shell CdS QDSSC
performance was observed after annealing the CdS quantum dots.
PCE was found to improve from 0.92% to 1.05% in solar cells fabri-
cated with quantum dots annealed at 100 ◦C; this further increased
to 1.10% upon annealing of the photoelectrodes at 150 ◦C. However,
when the photoelectrodes were annealed at higher temperatures,
the efficiency of the CdS QDSSC was observed to reduce, which
could be due to the formation of a thicker diffusion layer at the
Fig. 4. Energy band diagram of ZnO–Zn2SnO4 core–shell CdS quantum dot sensi-
tized solar cell showing the possible electrons transfer path (dashed line) in the
cell.
Fig. 3. Optical absorption spectra of CdS quantum dot sensitized ZnO–Zn2SnO4
core–shell photoelectrode with increasing number of SILAR cycles (from 5 to 25).

T. Bora et al. / Electrochimica Acta 68 (2012) 141–145
145
Table 3
performance with PCE of 0.92% was obtained for the core–shell CdS
QDSSC, which is ∼3.7 time higher than the PCE of the bare ZnO
nanorod CdS QDSSC (0.25%). Post annealing treatment of the CdS
QDs was found to play a crucial role on the solar cell performance
and enhanced PCE of 1.10% was achieved after annealing the QDs at
150 ◦C in N2 atmosphere, which was further improved to 1.24% by
inserting a thin layer of ZnS on the CdS QD surface to suppress elec-
tron recombinations at the QD/electrolyte interface. Various other
aspects of the core–shell QDSSC, like optimization of the Zn2SnO4
shell thickness, performance of the solar cell with different QDs as
sensitizer as well as different counter electrode catalyst materials,
etc. are currently under consideration as future study.
J–V characteristics of annealed ZnO–Zn2SnO4 core–shell CdS QDSSCs measured at 1
sun illumination (AM1.5, 100 mW/cm2).a
Annealing temperature (◦C)
Voc (V)
Jsc (mA/cm2)
FF (%)
Á (%)
100
150
200
250
0.72
0.73
0.68
0.65
3.30
3.44
3.20
2.65
44.09
43.65
37.80
37.01
1.05
1.10
0.82
0.64
a
The CdS QDs were deposited by 20 SILAR cycles and annealing was performed
in N2 atmosphere.
Acknowledgments
The authors would like to acknowledge the financial support
from Sheikh Saqr Al Qasimi Graduate Research Fellowship, Centre
of Excellence in Nanotechnology at the Asian Institute of Tech-
nology, Thailand and National Nanotechnology Center (NANOTEC)
of National Science & Technology Development Agency (NSTDA),
Royal Thai Government, for this research work.
Appendix A. Supplementary data
Supplementary data associated with this article can be found, in
the online version, at doi:10.1016/j.electacta.2012.02.036.
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4. Conclusions
In summary, Zn2SnO4 coated ZnO nanorod core–shell nanorod
arrays were synthesized hydrothermally and used for CdS QDSSC
applications. Due to the higher surface area and improved charge
transport, the ZnO–Zn2SnO4 core–shell CdS QDSSC exhibits much
higher photocurrent and photovoltage compared to the uncoated
ZnO nanorod CdS QDSSC. For 20 SILAR deposition cycles, optimum