Page 385 - Organic Electronics in Sensors and Biotechnology

362 Chapter Ten

implants. There is increased interest for application of these materials
in nanoscale assembly for advanced functional materials. 2
3
Organic electronics is a branch of electronics that deals with
(semi) conductive polymers, plastics, or small molecules. The field
of organic electronic devices is characterized by fast-paced progress
in both efficiency and device function. In addition to the prototypical
devices, such as organic light-emitting diodes (OLEDs), organic thin-
film transistors (OTFTs), and photovoltaic cells (OPVCs), many other
applications, e.g., sensors, memory cells, and light-emitting transis-
tors, have been demonstrated. The most intriguing benefits of using
organic materials include mechanical flexibility and light weight,
which makes this type of device most attractive for mobile applica-
tions or “smart clothing.” Moreover, entirely new design concepts for
consumer electronics have emerged, as organic electronic devices can
be adapted to follow complex surface shapes. For the past 40 years,
inorganic silicon and gallium arsenide semiconductors, silicon diox-
ide insulators, and metals such as aluminum and copper have been
the backbone of the semiconductor industry. However, there is a
growing research effort in organic electronics to improve the semi-
conducting, conducting, and light-emitting properties of organics
(polymers, oligomers) and hybrids (organic-inorganic composites)
through novel synthesis and self-assembly techniques. Performance
improvements, coupled with the ability to process these “active”
materials at low temperatures over large areas on materials such as
plastic or paper, may provide unique technologies, generate new
applications, and provide opportunities to address the growing needs
for pervasive computing.
The organic materials are often divided into two classes: small-
molecular materials and polymers. The fundamental properties of both
these classes are essentially the same, and the division mainly relates to
the way thin films are prepared. Small molecules are typically ther-
mally evaporated in vacuum whereas polymers are processed from
solution. Yet, most small-molecular materials are soluble as well, or
solubility can be increased by the synthetic addition of side chains.
Polymers have been utilized for fabrication of organic electronic devices
for decades. A report in 1977 on doped polyacetylene to achieve rela-
tively high conductivity opened up important new vistas for physics
and chemistry and for the technology in general. Early studies sug-
gested that a key feature of electronic polymers is a backbone consist-
ing of alternate single and double bonds resulting in a π-conjugated
network. This in turn leads to a small energy gap, enabling the appear-
ance of both semiconducting and metallic properties. Conductive
4
polymers are lighter, more flexible, and less expensive than inorganic
conductors. This makes them a desirable alternative for many applica-
tions. It also creates the possibility of new applications that would oth-
erwise be impossible using copper or silicon. Some of the other
applications include smart windows and electronic paper. In this