Electrode architectural engineering for enhancing solar conversion efficiency
Author
Khoo, Si Yun
Date of Issue
2016-04-16School
School of Chemical and Biomedical Engineering
Related Organization
GlobalFoundries
Abstract
Population explosion and significant advancement in technology have
dramatically increased global energy demand. Currently, fossil fuel-based power
generators remain as our primary power supply. However, fossil fuels are nonrenewable
energy resources and its combustion will result in severe environmental
problems. Therefore, there is an urgent obligation for our generation to develop
practical sustainable energy resources that will address the issue of dwindling fossil
fuels and reduce environmental degradation. The energy influx from the sun to earth
per hour is roughly equal to the yearly energy consumption across the world. There is
hence a general belief that photovoltaic (PV) devices are the most promising in
satisfying the drastically inflating energy demand.
The fast-expanding knowledge in nanotechnology and material science have
contributed to the development of nanomaterials with fascinating features. Integrating
materials nanotechnology in electrode design may bring us new opportunities to craft
groundbreaking next-generation devices. Electrode architectural engineering is
particularly important in fabricating high-performance PV cells to attain excellent
charge transport/transfer properties and desirable electrochemical reaction kinetics.
The mission of this interdisciplinary PhD program is to design novel electrode
architectures with favorable materials nanostructures and functional properties for
improving the solar conversion efficiency of low-cost PV devices, specifically
polymer PV devices and dye sensitized solar cells (DSSC), as well as to explore their
efficiency enhancement mechanisms, so as to push our current knowledge in electrode
design to a new frontier.
In order to improve the fill factor of polymer PV devices, uniformly distributed
gold nanoparticles (Au NPs) were inserted at the interface between vanadium
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pentoxide (V2O5) anodic buffer layer and ITO electrode to enhance the charge
extraction within the cell. The resultant power conversion efficiency (PCE) of the
modified device exhibited a ~16 % enhancement compared to the device without Au
NP. Theoretical impedance analysis revealed that a lower charge transport resistance
and higher charge recombination resistance, which are key factors leading to an
improved fill factor, of the modified OPV device. Moreover, the incorporation of Au
NPs have induced a better crystallinity of poly(3-hexylthiophene-2,5-diyl) (P3HT)
within the bulk heterojunction networks, hence resulting in enhanced charge
transportation process. This study provides new insights into the roles of Au NPs in
improving the performance of polymer solar cells.
Size-tunable TiO2 mesocrystals with high crystallinity were prepared using a
simple solvothermal approach and utilized as the photoanode material of DSSC. The
size of the TiO2 mesocrystals was controlled through tuning the hydrolysis rate of
titanium alkoxide precursor. The unique well-aligned mesocrystal structure enabled
efficient charge transportation pathway within the photoanode, while suppressing the
charge recombination at the TiO2/electrolyte interface. Furthermore, the submicronsize
mesoporous structure provided a large surface area for dye adsorption and
effective light scattering capability. The conversion efficiency of DSSCs was
significantly enhanced (~36 %) through the utilization of a mesocrystal TiO2-based
photoanode compared to that of a P25 controlled cell.
A novel interconnected NiCo2S4 nanosheets network was successfully grown on
fluorine-doped tin oxide (FTO) and applied as the counter electrode (CE) of DSSC.
Detailed studies revealed that the compositional ratio of NiCo2S4 could significantly
affect its catalytic activity in redox mediator regeneration. Furthermore, the
development of interconnected nanosheets on electrodes could substantially increase
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the electrochemically active surface area, thus leading to the improved kinetics of Iregeneration
reactions. DSSC assembled using the optimal interconnected NiCo2S4
nanosheets CE exhibited a higher power conversion efficiency (7.22 %) compared to
that of a conventional device (6.87 %) employing sputtered Pt CE.
Subject
DRNTU::Engineering::Materials::Energy materials
DRNTU::Engineering::Electrical and electronic engineering::Semiconductors
DRNTU::Engineering::Electrical and electronic engineering::Semiconductors
Type
Thesis
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