Introduction - Low-cost Nanomaterials: Toward Greener and More Efficient Energy Applications - page 4

2 Pyrite Solar Cells
Pyrite (iron disulfide (FeS 2 ), also known as fool's gold) has long been proposed as a
green solar cell material owing to its optimum band gap (i.e., 0.95 eV), high optical
absorption coefficient (i.e., greater than 10 5 cm -1 , two orders of magnitude greater
than the absorption coefficient of silicon), and abundance on earth, making it pos-
sible to fabricate highly efficient thin film solar cells with largely decreased con-
sumption of raw materials. However, unanswered questions about the effects of
defects and techniques to grow pure crystalline material still remain. In the chapter
by Ren et al., the crystal structure and fundamental properties of pyrite are first
introduced to offer an overview as to why it is a promising material for photovoltaics,
followed by the detailed review on various synthetic methods for the preparation of
nanostructured pyrite with a focus on the most recently developed solution phase
synthesis of pyrite nanoparticles. In the last section of this chapter, the applications
of nanostructured pyrite for photovoltaics and photodetectors are presented.
3 Polymer-Based Solar Cells
Many organic semiconductors exhibit the electronic properties of their inorganic
counterparts while carrying the advantages of plastic processing and low fabri-
cation cost through well-established polymeric materials processing techniques,
thereby yielding a variety of organic-based electronic devices such as organic
photovoltaic devices (OPVs), organic light emitting diodes (OLEDs), organic thin
film transistors, etc. Organic photovoltaic devices have been regarded as promising
technologies for the conversion of solar energy to electricity due to their light
weight, flexibility, and cost-effective processibility. Additional advantages of
OPVs also include short energy payback time compared to existing photovoltaic
devices, non-toxic, and abundance on earth. In a chapter contributed by Fang-
Chung Chen et al., the fundamentals of OPVs are presented in detail, followed by a
comprehensive review on the recent progress on conjugated polymer-based OPVs.
Effects of thermal annealing, solvent annealing, and interface engineering on the
performance of OPVs are also discussed. In the last section of this chapter,
common optical methods used to improve light absorption in OPVs are summa-
rized, followed by an overview of the development of low-band gap conjugated
polymers for more efficient light harvesting.
Indium tin oxide is the most commonly used transparent conductive materials
for a wide range of electronic devices such as OPVs. However, ITO usage is
diminished due to high material cost and poor flexibility. Clearly, the development
of a low-cost replacement for ITO is crucial for the commercial feasibility of
OPVs and other organic-based electronic devices. In this regard, a variety of
nanomaterials have been investigated that have shown great potential as an ITO
replacement by providing comparable or better electronic and optical properties. In
the chapter by Krebs et al., the development of ITO-free polymer solar cells is