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|Title: ||Studies of ZnO nanostructure-based dye sensitized solar cells (DSSCs)|
|Other Titles: ||Na mi jie gou yang hua xin ran liao min hua tai yang neng dian chi zhi yan jiu|
|Authors: ||Cheung, Wing Sze (張穎思)|
|Department: ||Department of Physics and Materials Science|
|Degree: ||Master of Philosophy|
|Issue Date: ||2010|
|Publisher: ||City University of Hong Kong|
|Subjects: ||Dye-sensitized solar cells.|
Zinc oxide thin films.
Solar cells -- Materials.
|Notes: ||CityU Call Number: TK2960 .C45 2010|
xiv, 100 leaves : ill. (some col.) 30 cm.
Thesis (M.Phil.)--City University of Hong Kong, 2010.
Includes bibliographical references (leaves 86-99)
|Abstract: ||The energy crisis and soaring oil price have triggered the development of
photovoltaic technology. Silicon (Si) based solar cell devices have dominated the market
for the past decades. However, the high demanding and processing cost of crystalline Si
have limited their applications and at the same time encouraged the development of simple
and low cost alternatives. Dye-sensitized solar cells (DSSCs) utilizing nanostructured
materials have been considered as one of the promising candidates for photovoltaic devices.
In this dissertation, a low temperature hydrothermal growth method to synthesize
one dimensional ZnO nanorods arrays (ZNAs) on indium doped tin oxide (ITO) substrates
from a zinc salt for DSSCs application is demonstrated. By adjusting the reaction times,
ZNAs with different morphologies resulted. The length of nanorods (NRs) increased
directly proportional to the total reaction times along the  direction of its hexagonal
wurtizite (WZ) structure, whereas the diameters of NRs increased at a slower rate.
However, the thickening effect of NRs reduced the surface area for dye loading in DSSCs
application and worsened the performance of the cell.
The morphologies of hydrothermal growth NRs were not only affected by the
conditions of hydrothermal growth but also the ZnO seed layer which acts as homogeneous
nucleation sites for the growth of NRs. Through the tuning of the Ar:O2 ratio in the seed
layer deposition process using a pure Zn target by radio frequency (r.f.) magnetron
sputtering, ZnO seed layers with different properties resulted and subsequently influenced the NRs based films. The growth rate of NRs was found to be increased with the oxygen
flow rate during the seed layer deposition process. The orientation of the NRs along the
 direction perpendicular to the ITO substrate was improved at the same time.
In a relatively short period of the hydrothermal growth reaction, hybrid NRs and
nanosheets (NSs) complexes could result. To further optimize the morphologies for DSSCs
application, a highly branched polymer additive, poly(ethylenimine) (PEI), was added to
the hydrothermal growth solution bath. The growth of NRs along the c-axis perpendicular
to the substrate was promoted and the existence of NSs structure in the film remained for a
longer reaction time.
The above ZnO nanostructures based films grown on the ITO substrates served as
the photoelectrode for fabricating DSSCs. They were dipped into a commercial ruthenium
dye, known as N719, for the dye adsorption process. After the application of an iodinebased electrolyte, with a platinum catalyst and fluorine doped tin oxide (FTO) as the counter-electrode, the sandwiched DSSCs were sealed and tested using simulated sunlight
of AM 1.5. The current-voltage responses of the cells were recorded. The overall
conversion efficiencies ranged from 0.3% to more than 1.2% and were found to be highly
dependent on the morphologies and nanocrystalline structures of the ZnO based
photoelectrodes. These findings helped in optimizating the performance of ZnO
nanostructures based DSSCs fabricated by a low cost and simple route.|
|Online Catalog Link: ||http://lib.cityu.edu.hk/record=b3947650|
|Appears in Collections:||AP - Master of Philosophy |
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