Page 315 - Organic Electronics in Sensors and Biotechnology

292 Chapter Seven

Depending on signal level and wavelength and needed signal infor-
mation, most often semiconductor-based detectors, photomultipliers,
or spectrophotometers are employed. Lock-in amplifiers and boxcar
integrators offer a high sensitivity sensing when combined with these
detectors.
Organic semiconductor-based detectors would, of course, be an
interesting alternative to these standard techniques. The possibilities
offered by organic devices regarding integration and low-cost manu-
facturing render such devices very attractive for integration in optical
sensor systems.
Research activities in the field of photodetectors are mainly driven
by the strong interest in organic solar cells as a future cost-efficient
6, 5
way to generate electricity. The rapid progress in device efficiencies
also led to investigations of the usage of organic materials in photo-
detectors. Optical sensor systems as well as optical data transfer
3, 4
98
setups comprising organic photodiodes (OPDs) have been demon-
strated. Even a complete data transmission system using solely
99
organic optoelectronic devices was presented. 23, 100 A high sensitivity
to light pulses is one key factor in these applications.
For certain sensing schemes, a fast photoresponse of the detectors
is important. The fastest photodetectors today are fabricated using
small-molecule materials. 101, 102 They show response times in the nano-
second regime, but unfortunately their fabrication is relatively compli-
cated due to the needed multilayer structures. Advances in the
temporal response of photodiodes made of polymer materials show
their prospects. 103, 104 Figure 7.26 shows the temporal behavior of the

Time (ns)

FIGURE 7.26 Normalized pulse response of a P3HT:PCBM photodiode
following a 1.6 ns laser pulse with a wavelength of 532 nm. The FHWM of
the −5 V biased device is 11 ns. (Reprinted with permission from Ref. 104.
Copyright 2007, American Institute of Physics.)