Introduction - Low-cost Nanomaterials: Toward Greener and More Efficient Energy Applications - page 3

band structure, photostability, chemical inertness, and well-established synthesis
methods. Modification of TiO 2 has been extensively investigated in recent years.
The aim is to improve charge collection and charge transport in DSSCs, including
the development of TiO 2 nanostructures with high surface area and unique mor-
phologies and the preparation of doped TiO 2 nanostructures with improved optical
and electronic properties.
In the chapter by Lin et al., various synthetic methods for the preparation of
nanostructured TiO 2 are presented, including sol-gel, hydrothermal/solvothermal,
electrochemical anodization, and electrospinning/electrospray methods. These
methods produce a wide range of TiO 2 nanostructures that meet the requirements
of many different applications. In the second section of this chapter, an overview
of how the modification of TiO 2 influences its chemical/physical properties in
different optoelectronic devices is presented.
In the chapter by Ma et al., nitrogen-doped TiO 2 nanostructures and their effect
on the performance of DSSCs are described. Various doping methods, nano-
structures, the resulting physiochemical properties of N-doped TiO 2 , and the effect
of N-doped TiO 2 photoanode on the performance of DSSCs devices are discussed
in detail. In the last section of this chapter, an analysis of the electron kinetic
behaviors (i.e., charge transport, electron lifetime, and charge recombination) in
DSSCs based on N-doped TiO 2 photoanodes is presented.
In another chapter contributed by Ma et al., recent progress on the development
of Pt-free counter electrodes for DSSCs is comprehensively reviewed. Platinum-
based counter electrodes are commonly used in current DSSCs. However, its high
cost has motivated the search for low-cost, high performance alternatives,
including carbon materials, conductive polymers, transition metal compounds, and
composite catalysts. The advantages and disadvantages of each Pt-free counter
electrode alternative are subsequently reviewed.
An analog to DSSCs, quantum dot-sensitized solar cells (QDSSCs) in which
quantum dots play the role of ''dye'' in DSSCs have been extensively explored in
recent years primarily due to the exceptional optoelectronic properties of quantum
dots (e.g., size-dependent optical properties and MEG characteristics) and the
well-established synthetic methods for the preparation of high quality quantum
dots with tuneable morphologies and compositions. In a chapter by Mora-Seró
et al., recent advances in the development of QDSSCs are presented with a focus
on highlighting the differences between quantum dot- and dye-sensitized solar
cells (QDSSCs vs. DSSCs) in several aspects, including the preparation of sen-
sitizers, nanostructured electrodes, hole transporting materials, counter electrodes,
and recombination and surface states. Through such comparisons, further
improvements on QDSSCs can be envisioned. One example is the recent break-
through in photovoltaics with organometallic halide perovskites which came about
through the intensive study on QDSSCs. This is presented in detail in the last
section of this chapter.