1.1 Organic Semiconductors: History and Applications

For the past fifty years, inorganic semiconductors such as silicon and gallium arsenide silicon dioxide insulators, and metals such as aluminum and copper have been the backbone of the semiconductor industry. However, in 1977 the first highly conducting polymer, chemically doped polyacetylene [1] was discovered, which demonstrated that polymers could be used as electrically active materials as well. This discovery resulted in a huge research effort on conjugated organic materials. In the earlier time, the performance and stability of organic semiconductors were very poor. However, with drastic improvements in synthesis and processing of new classes of molecular materials such as conjugated polythiophenes in the past two decades [2], the prospects of commercially using organic semiconductors in applications such as organic light-emitting diodes (OLEDs), field-effect transistors (OFETs) and solar cells are now greater than ever [3,4,5]. In fact, in 2002 Philips introduced the Sensotec Philishave [6] as the first product in the market featuring a display panel based on OLED technology, and following that, Kodak has introduced [6] the Kodak EasyShare LS633 digital zoom camera with an award-winning OLED display technology. Sony produced 27-inch protype OLED TV with a contrast ratio of greater than $10^{6}$ and NTSC color reproduction $\geq 100$ (Fig 1.1). Simplicity in manufacturing and lower costs of organic devices have been the primary reasons driving these devices towards commercialization.

Figure 1.1: Two examples of use of OLEDs in commercial products. The image on the left shows a new Philips shave introduced to the market in 2002. The image on the right shows the OLED TV produced by Sony recently. Images were taken from [6].