Quantum Dot-Sensitized Solar Cells - Low-cost Nanomaterials: Toward Greener and More Efficient Energy Applications - page 87

power during the last period of industrialization is compensated with the use of
nonrenewable sources, fossil fuels such as coal and oil. Their use not only rep-
resents an irreplaceable depletion of stocks, avoiding its use on other beneficial
issues especially in the case of oil, but it has caused serious side effects as the
greenhouse effect. Gases from combustion have a potentially catastrophic impact
in the global warming and the climate change as it has been recognized since the
end of the twentieth century by the United Nations [ 2 ]. In this sense, energy has
become one of the most striking problems of the humankind. It is easy to recognize
that the energy problem is not only important in itself but for its implications in
many of the great challenges of humanity in the twenty-first century (wars,
environment, food, water…). This situation strongly demands a change in the
weighting of the different energy sources in the energy cocktail that powers the
world. The weight of nonrenewable energy sources necessarily has to decrease,
even if this decrease in nonintentional due to the stock reduction. It is debatable
whether the size of the nonrenewable energy source reserves is large or small, but
the irrefutable fact is that these reserves are finite. On the other hand, to maintain
the economic development the energy consumption cannot be significantly
decreased, and the reduction of energy from nonrenewable sources has to be
compensated with power coming from renewable sources.
Undoubtedly photovoltaic energy is the renewable power source with higher
potentiality, as the Earth receives from the Sun in just 1 hour the same amount of
energy that it is expended by all the humankind in 1 year [ 3 ]. But the devices that
we currently have to harvest energy from this huge pool, they are expensive
compared to other energy sources. In this sense, a reduction of cost in photovoltaic
devices is mandatory to take full advantage of the tremendous potentialities of
these systems. There are two ways to attain this scope: (i) reducing the fabrication
cost of the device; (ii) increase the efficiency of the photovoltaic devices. To attain
both solutions nanoscience can help us.
The new technologies capable of constructing material structures with dimen-
sions from 0.1 to 50 nm have opened numerous possibilities to investigate new
devices in a domain heretofore inaccessible to the investigators and technologists.
A considerable activity exists in nanoscience and technology in university and
industrial laboratories around the world. The requirements of improved efficiency
and versatility, and of reduced cost of the photovoltaic devices, have led to search
for extending the field of traditional study in inorganic semiconductors, incorpo-
rating new materials, and structures capable of satisfying these requirements. In
the field of the photovoltaic solar power, the challenge of the future for the new
concepts on nanoscale is to reduce the present cost of the devices by a factor
10-100. Candidates to lead this revolution are the new nanocomposite solar cells,
formed by coatings deposited from liquid solutions. These procedures avoid the
need of treatment in vacuum, and improve substantially the time and cost of
production. Also the highly energetic stages of the process of production are
avoided, improving the time of recovery of the spent energy. With the advanced
optimization on nanoscale, and the application of solution low cost, it is possible to
achieve the efficient use of minuscule quantities of matter.