2015 ahmed kamal al-kamal all rights reserved

53 Pages·2014·2.05 MB·English

©2015

AHMED KAMAL AL-KAMAL

ALL RIGHTS RESERVED

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SYNTHESIS OF Ag-DOPED TiO NANOPARTICLES by COMBINING
2
LASER DECOMPOSITION OF TITANIUM ISOPROPOXIDE AND
ABLATION OF Ag FOR DYE-SENSITIZED SOLAR CELLS
By
AHMED KAMAL AL-KAMAL

A Thesis submitted to the
Graduate School-New Brunswick
Rutgers, the State University of New Jersey
In partial fulfilment of the requirements
For the degree of
Master of Science
Graduate Program in Materials Science and Engineering
Written under the direction of
Prof. Bernard Kear
And approved by
___________________________
________________________

____________________

New Brunswick, New Jersey
JANUARY, 2015
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ABSTRACT OF THE THESIS
SYNTHESIS of Ag-DOPED TiO NANOPARTICLES by COMBINING
2
LASER DECOMPOSITION of TITANIUM ISOPROPOXIDE and
ABLATION of Ag for DYE-SENSITIZED SOLAR CELLS
By
AHMED KAMAL AL-KAMAL
Dissertation Director
Prof. Bernard Kear

Nanostructured powders of TiO and Ag-doped TiO are synthesized by a novel
2 2
pulsed-laser process that combines laser ablation of a silver (Ag) disc with laser
decomposition of a titanium tetra-isopropoxide (TTIP) solution. Nanoparticles are formed
by rapid condensation of vaporized species in the plasma plume generated by the high
power laser, resulting in the formation of rapidly quenched Ag-doped TiO nanoparticles
2
that have far-from-equilibrium or metastable structures. The uniqueness of the new
ablation process is that it is a one-step process, in contrast to the two-step process
developed by previous researchers in the field. Moreover, its ability to synthesize an
extended-solid solution phase of Ag in TiO may also be unique. The present work
2
implies that other oxide phases, such as Al O , MgO and MgAl O , can be doped with
2 3 2 4
normally insoluble metals, such as Pt and Ir, thus opening new opportunities for catalytic
ii
applications. Again, there is the prospect of being able to synthesize nanopowders of
diamond, c-BN, and mixtures thereof, which are of interest for applications in machine
tools, rock-drill bits, and lightweight armor.
A wet-chemistry method is also investigated, which has much in common with that
adopted by previous workers in the field. However, photo-voltaic properties do not
measure up to expectations based on published data. A possible explanation is that the
selected Ag concentrations are too high, so that recombination of holes and electrons
occurs via a quantum-tunneling mechanism reduces photo-activity. Future work,
therefore, will investigate lower concentrations of Ag dopant in TiO , while also
2
examining the effects of metastable states, including extended solid solution, amorphous,
and semi-crystalline structures.

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Dedication

With a heart full of love, longing and anguish, I dedicate this thesis
to my deceased Mother. Although our time together was curtailed,
her contributions to my life will be felt forever. Also, I dedicate this
thesis to my great father who has always supported and
encouraged me. I would not be who I am today without the love
and support of my parents.

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Acknowledgments
I would like to express my deepest gratitude to my advisor, Prof. Bernard
Kear, for his outstanding guidance, caring and patience. I would like to
thank my co-advisor, Prof. Stephen Tse, for his support and advice. I would
like to thank my thesis committee member: Prof. Lisa Klien for her
encouragement and insightful suggestions. Many thanks go to Dr. Jafar Al-
Sharab for his help, encouragement and advice. Special thanks to Robert
Horvath for his guidance in proper use of the materials characterization
equipment. I am most grateful to all my lab-mates, particularly Hadi Halim,
Dr. Gang Xiong and Dr. Zhizong Dong for their support and suggestions. I
would like to acknowledge, with much appreciation, the crucial role of my
friends, Hasan Snedeh, Nofel Wohieb, Kutaiba Al-Marzouki, Nawras Jawad,
Adil Sobhi and Ahmed Sarhan. Last, but no means least, many thanks to my
brothers, Mustafa, Mahmood, Sohaib and Zaid for their support and best
wishes.

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Table of Contents

Abstract ……………………………………………………………......ii
Dedication……………………………………………………................iv
Acknowledgments……………………………………………………....v
Table of Contents ………………………………………………………vi
List of Tables ……………………………………………………………viii
List of Figures …………………………………………………………...ix

CHAPTER 1: INTRODUCTION ……………………………………….1
1.1 Dye-sensitized solar cell ……………………………………….. 1
1.2 Operational aspects ……………………………………………...2
1.3 Photovoltaic efficiency …………………………………………..4
1.4 Efficiency measurements ………………………………………..5

CHAPTER 2: MATERIALS SELECTION ……………………………. 6
2.1 Doping of TiO …………………………………………………... 6
2
2.2 Ag-Doping of TiO …………………………………..……….….. 8
2

CHAPTER 3: MATERIALS SYNTHESIS …………………..………… 9
3.1 Solid-phase ablation ………………………………………….…. 9
3.2 Liquid-phase ablation ……………………………………….……9
3.3 Ablation mechanism and kinetics …………………………..….10
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3.4 Thermodynamic aspects ……………………………………… 13
3.5 Kinetic aspects …………………………………………………13

CHAPTER 4: ANALYTICAL TECHNIQUES ……………………….15
4.1 FE-SEM analysis ……………………………………………….15
4.2 HR-TEM analysis …………………………………………........15
4.3 XPS analysis………………………………………………..……16
4.4 XRD analysis …………………………………………….……..16
4.5 Photovoltaic analysis………………………………..………….16
CHAPTER 5: RESULTS AND DISCUSSIONS………………………17
5.1 Pulsed-laser synthesis of TiO ……………………….………..17
2
5.2 Pulsed-laser synthesis of Ag-doped TiO ……………….……20
2
5.3 Wet-chemical synthesis of Ag-doped TiO …………………..26
2
5.4 Preparation and testing of a solar cell …………………….…31

CHAPTER 6: CONCLUSIONS AND FUTURE WORK …………...35

REFERENCES…. ………………...........................................................37

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List of Tables
Table 1 - Synthesis of nanoparticles by LP-PLA ………………………………… 10
Table 2 - Measured d-spacings for Ag-doped anatase TiO , before and after heat
2
treatment …………………………………………………………………………… 25

Table 3- SEM-EDS spectra Patters of various nanostructured of TiO and TiO /Ag
2 2
samples heat treated 450 and 600 °C ……………………………………………30
Table 4- Photovoltaic properties of DSSCs ……………………….…………...….…33

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List of Figures
Figure 1 - Schematic representation of a dye-sensitized solar cell ……………………..2
Figure 2 - Schematic of DSSC operation……………………….…………………...….3
Fig 3 - Photovoltaic array voltage/current characteristics of DSSCs …………………4
Figure 4 - Schematic diagram of the experimental LP-PLA apparatus ……………...11
Figure 5 - Evolution of laser-induced plasma in liquid phase…………………………12
Figure 6 - Laser ablation rate of Si vs water layer thickness above Si surface ……….14
Fig 7 - Schematic of expiremental set-up for laser decomposition of TTIP ………….18
Fig 8- SEM micrograph of LIPP synthesized TiO2 …………………………………..19
Figure 9 - XRD pattern of TiO2 powder. Peaks matches well with anatase phase …19
Figure 10 - (a) HRTEM image, and (b) corresponding diffraction pattern of
nanostructured TiO2 synthsized by laser decomposition of TTIP …………………..20
Fig 11 - Experimental set-up for combining laser ablation of Ag and decomposition of
TTIP ……………………………………………………………………………………21
Fig 12 – SEM micrographs and EDS spectra of TiO2/Ag nanomaterials synthesized by
laser………………………………………………………………………………………22
Fig 13- HRTEM images, and corresponding SAED pattern for TiO2/Ag synthesized by
laser………………………………………………………………………………………23
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