The present work addresses several issues in the field of organic and transparent
electronics. One of them is the prevailing high power consumption in state-of-the-art
organic field-effect transistors (OFETs). A possible solution could be the
implementation of complementary, rather than unipolar logic, but this development is
currently inhibited by a distinct lack of high performance electron transporting (n-channel)
OFETs. Here, the issue is addressed by investigating a series of solution
processable n-channel fullerene molecules in combination with optimized transistor
architectures. Furthermore, the trend towards complementary circuit design could be
facilitated by employing ambipolar organic semiconductors, such as squaraine
molecules or polymer/fullerene blends. These materials can fill the role of p- or n-channel
semiconductors and enable the facile implementation of power saving
complementary-like logic, eliminating the cost-intensive patterned deposition of
discrete p-and n-channel transistors. Alternatively, a patterning method for organic
materials adapted from standard photolithography is discussed. Furthermore,
ambipolar FETs are found to be capable of light sensing at wavelength of 400-1000
nm. Hence their use in low-cost, organic based optical sensor arrays can be envisioned.
Another strategy to reduce the power consumption and operating voltages of
OFETs is the use of ultra-thin, self-assembled molecular gate dielectrics, such as
alkyl-phosphonic acid molecules. Based on this approach solution processed n- and p-channel
OFETs and a complementary organic inverter circuit are demonstrated, which
operate at less than 2 Volts.
Finally, transparent oxide semiconductors are investigated for use in thin-film
transistors. Titanium dioxide (TiO2) and zinc oxide (ZnO) films are deposited by
means of a low-cost large area compatible spray pyrolysis technique. ZnO transistors
exhibit high electron mobility of the order of 10 cm2/Vs and stable operation in air at
less than 2 Volts. These results are considered significant steps towards the
development of organic and transparent large-area optoelectronics.