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|Title: ||Fabrication and characterization of zinc oxide (ZnO) nanowires array and its applications|
|Other Titles: ||Yang hua xin na mi xian jing lie de zhi zao, fen xi he ying yong|
|Authors: ||Leung, Yu Hang ( 梁宇恆)|
|Department: ||Department of Physics and Materials Science|
|Degree: ||Doctor of Philosophy|
|Issue Date: ||2011|
|Publisher: ||City University of Hong Kong|
|Notes: ||CityU Call Number: TK7874.85 .L48 2011|
xi, 107 leaves : ill. (some col.) 30 cm.
Thesis (Ph.D.)--City University of Hong Kong, 2011.
Includes bibliographical references.
|Abstract: ||Since the discovery of carbon nanotubes by Iijima in 1991, extensive efforts
have been put on the research of the synthesis and characterization of different kinds of
materials in nano-scale. The new phenomena or properties found on nanostructured
materials attract great interest not only on their potential applications, but also on
theoretical studies. Recently, great attention has been paid on the research of
nanostructures of different semiconducting materials, such as Si (group IV), GaN
(group III-V), ZnO (group II-VI), etc. ZnO is recognized as a promising candidate for a
broad range of applications in optoelectronics, gas sensing, piezoelectrics, etc.
ZnO is a semiconductor material with wide bandgap (3.37 eV) and high exciton
binding energy (60 meV). These properties make ZnO a suitable candidate for short
wavelength photonic/optoelectronics applications. Recently, a huge variety of ZnO
nanostructures has been fabricated. However, commercially-viable applications based
on ZnO nanostructures are scarce due to the high cost, critical processing conditions,
and complicated processing techniques. In this study, ZnO nanowires arrays were
fabricated with a simple, highly reproducible and controllable hydrothermal method.
The nanowires were found to be vertically-aligned and grown along the c-axis. More
importantly, the nanowires covered uniformly across the whole substrate. This allows
the fabrication of devices over a large area, and it is advantageous especially in
applications like light-emitting diodes, or photovoltaics, etc.
The resultant arrays were utilized in two practical applications: visible-blind UV
photodetectors (PD) and dye-sensitized solar cells (DSSC). The UV PD consisted of a
ZnO nanowires array p-n homojunction. The junction was composed of hydrothermally
grown n-type ZnO nanowires array covered with p-type Al, N co-doped ZnO film by a
sol-gel method. The homojunction exhibited good rectification characteristics, with
reverse leakage current and rectification ratio of ~5 µA and ~150, respectively at a bias
of 3 V. The PD had peak responsivity to light with wavelength of 384 nm with
UV-visible responsivity ratio of ~70 at an operating bias of -3 V. The ZnO
nanowires-based DSSC was built similar to the TiO2-based Grätzel cell. Under AM 1.5
simulated sunlight with intensity of ~100 mW/cm2 (1 Sun), the DSSC had an
open-circuit voltage (VOC) of ~0.68 V and a short-circuit current density (JSC) of ~3.5
mA/cm2. The fill factor (FF) and light conversion efficiency (ƞ) were ~0.42 and ~1%
respectively. In this work, a simple but reasonably effective encapsulation was
employed in our cells. The efficiency of the cells remained stable at a range of 0.9-1%
after storage time of over a month, suggesting that the cells were effectively
|Online Catalog Link: ||http://lib.cityu.edu.hk/record=b4086290|
|Appears in Collections:||AP - Doctor of Philosophy |
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