Organic materials consist of long chains of protein molecules repeatedly linked with smaller carbon-based molecules (hence the term "organic"). Unlike semiconducting crystals, which are small interlocking molecules, organic polymer semiconductors are composed of very large, chainlike molecules repeatedly linked with smaller carbon molecules.
Like all of the things that foster life, air and water also affect organic semiconductors like OLEDs, but they do so negatively. The corrosive effects of oxygen, moisture and high temperatures lead to "denaturing" in any organic molecule. Denaturing means the long complex folded interlocking strands of the organic molecule unravel, thereby eliminating its former functions.
In living things, denaturing means the protein dies; in organic semiconductors, it's just as bad.
Fortunately, it's also just a matter of time until these problems are engineered away, even if the chemists don't come up with a weatherproof polymer formula anytime soon. Either way, organic semiconductors open up a brave new world. For instance, at the other end of the solar spectrum-absorbing light rather than emitting it-plastic solar cells that embed semiconducting nanocrystals in a polymer-are creating a flexible, lower-cost alternative to solar cells fashioned atop silicon wafers.
From plastic solar cells to plastic magnets to plastic displays to ink-jet-printed circuitry using organic semiconductor "ink," the advantage of organic films is cost, cost, cost over a wide, wide, wide area. Even if their performance remains in the fraction-of-a-MHz range, compared with the 10,000-fold faster GHz speeds of silicon chips, organic semiconductors are here to stay.
Instead of processing wafers at thousands of degrees, polymer-based semiconductors can be fabricated at tens of degrees. Instead of requiring pure crystalline silicon wafers as a substrate, organic semiconductors can make due with a preparatory polymer film sprayed on almost any surface-say the wall of your family room, or the side of a building. Instead of diffusion, defects and doping, with organic semiconductors all you have to do is mix up the chemicals slightly differently, to tailor the materials compared to the expense, time and specialized high-temperature equipment needed to process silicon as a semiconductor.
Two possible solutions to organic semiconductor's "big problem" exist: firstly, modifying the formulae; second, encapsulation.
The first method is best. If organic semiconductors can be formulated to make them more stable in harsh environments, such a "weather-proof" organic material would require no encapsulation. Just such a formulation is being sought by the inventor of the plastic magnet, University of Nebraska professor Andrzej Rajca. "Magnetic polymers were predicted more than 30 years ago, and a large volume of work has been done on this," said Rajca.
Second, while chemists painstakingly search for the right formulation, engineers nevertheless are perfecting inexpensive encapsulation methods. For instance, Iowa State University recently engineered an ultrathin polymer coating for protecting delicate microelectromechanical systems (MEMS). The self-assembled process provides MEMS parts with a permanent coating that reduces friction and repels environmental contaminants.