On the Development of Colloidal Quantum Dot Sensitized Solar Cell Architectures Ghada Hamdi Mohamed Ahmed

Supervisor: Mohamed Sabry

Thesis (M.A.)—Nile University, Egypt, 2014 .

"Includes bibliographical references"

Contents:
Nanotechnology and solar energy
Solar cells and photovoltaic generations
First generation solar cells
Second generation solar cells
Third generation solar cells
Organic solar cells
Dye sensitized solar cells
Quantum dot sensitized solar cells
Structure and design
Working mechanism
Methods for fabrication of the QDSSC photoelectrodes
Recently proposed Pseudo-SILAR solar paint
Our Novel proposed physical mixing method
QDSSC characterization and performance parameters
Motivation and Literature Review
Why Quantum dots as sensitizers?
Multiple Exciton Generation
. Cadmium Selenide (CdSe
Zinc Oxide (ZnO
An Overview of the Dissertation work
CHAPTER 2: EXPERIMENTAL PROCEDURE AND CHARACTERIZATION
Instrumentation
The prepared nanomaterials
Transmission Electron Microscopy (TEM
Absorption and Fluorescence spectra
X-ray Diffraction
Thin film Characterization
SEM
Optical measurements of thin films
The sensitized solar cells (Fabrication and Characterization Needed Devices
2.2.3.1. Spin coater
2.2.3.2. Muffle furnace for thin film annealing
2.2.3.3. Keithley source meter
2.2.3.4. Solar simulator
2.3. Methodology
2.3.1. Preparation of ZnO and Au-ZnO nanocones by microwave irradiation method
2.3.2. Preparation of CdSe quantum dots by organometallic pyrolysis method
2.3.3. Preparation of the polysulphide electrolyte
2.3.4. Fabrication of ZnO or Au-ZnO/ CdSe based electrodes
2.3.5. Detailed fabrication steps for mixed and layer-by-layer method
CHAPTER 3: RESULTS AND DISCUSSION
3.1. The Prepared nanomaterials (TEM, Absorption- photoluminescence, and XRD
3.1.1. Characterization of ZnO nanopyramids
3.1.2. Characterization of Au-ZnO nanopyramids
3.1.3. Characterization of CdSe quantum dots
3.2. The prepared thin films: (Optimization, Optical characterization and SEM
3.2.1. Optimization
3.2.2. SEM and surface morphology
3.2.3. Optical measurements
3.3. The constructed solar cells (Solar cell performance

Abstract:
Quantum dot sensitized solar cells (QDSSCs) have attracted a widespread attention over
the past few years as a prospects of fabricating highly efficient, low cost third generation
photovoltaics. Quantum dots (QDs) –The light harvesting material in the solar cell– such
as CdSe, CdTe and CdS exhibit size-dependent band gaps which offer great opportunities
for harvesting light energy in the visible and infrared regions of the solar spectrum. In
addition, due to impact ionization effect, it is possible to utilize hot electrons in QDs to
generate multiple electron–hole pairs per photon of light absorption. These features give
to QDSSCs the capability to achieve conversion efficiencies beyond the Shockley–
Queisser limit, and provide a transformative improvement to traditional silicon
photovoltaic cells.
Currently available QDSSCs fabrication procedures utilize a series of deposition steps to
achieve a better performing photoanode. Semiconductor film deposition and annealing
techniques are time-consuming processes, requiring multiple steps and several days to
achieve the best performing photoelectrode. In order to produce more functional and
economically viable QDSSCs, it is important to simplify the electrode preparation
techniques. Therefore, this study presents a novel method for casting the quantum dot
onto the semiconductor based electrode by directly mixing the photoanode components
together without a molecular linker, which offers easier scaling up process while
maintaining a very low cost. This method was compared with layer-by-layer method and
showed an improvement in the overall cell performance parameters.
In addition, this work focuses on applying uniform-sized hexagonal pyramid-shaped ZnO
and Au-ZnO nanoparticles for the first time in QDSSCs. The as-prepared nanoparticles
possess excellent optical, catalytic and electrical properties. Furthermore, another Au
nanoparticles layer/ZnO based QDSSC was constructed and compared with Au-ZnO
hybrid structure in order to figure out the plasmonic effect of Au nanoparticles on the
QDSSC light absorption behavior.
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The results showed that the cells incorporating the Au nanoparticles layer/ZnO electrode
exhibited the highest cell efficiency of = ~0.1% compared to other cells based on bare
ZnO or Au-ZnO hexagonal nanopyramid-shaped. The results also suggest that metal
nanoparticles (NPs) are potentially useful for improving the photoresponse in QDSSCs.
However, for effective charge separation, these metal (NPs) should be isolated or
separated from the wide band gap material and the sensitized material.

Text in English, abstracts in English and Arabic