Semiconductors or silicon? The traditional material for electronic component parts of all kinds could soon be in for serious competition. At any rate, this is what scientists are hoping who have made and examined the properties of new semiconductors consisting of organic materials, i.e. materials based on carbon. With the support of the Deutsche Forschungsgemeinschaft (DFG), junior scientist Dr. Jan Hendrik Schön from Constance has examined the electronic properties of organic semiconductors made of pentacene with a research team at the Bell Laboratories in Murray Hill, New Jersey. Organic semiconductors of this kind are promising candidates for, say, organic solar cells.
Semiconductors are substances that acquire conductivity, i.e. allow electrical charges to be transported through them, once they are exposed to light or heat. At low temperatures, however, they act as insulators. This property can be controlled by adding carefully dosed amounts of chemical elements, which experts call "doping". Semiconductor elements form the basis of all electronic applications, whether it be in computers, flat screens, data storage systems or solar cells.
Only little is known about how the transport of charges actually works in organic semiconductors. This knowledge is needed to optimise material for future applications. For organic semiconductors bear a number of advantages. They are easy to manufacture and process, and unlike silicon, they can be applied to flexible surfaces. Moreover, they are very cheap. Experts are hoping that printing methods could be used to manufacture circuits by the yard.
Jan Hendrik Schön and his colleagues examined the hydrocarbon pentacene and related organic substances with regard to their suitability as semiconductors. They discovered that some of them could be used to make transistors combining the properties of two previously known types of semiconductor. This insight can pave the way for a considerable simplification of circuit manufacture.
Schön and his colleagues also succeeded in significantly improving the efficiency of organic solar cells. Pentacene doped with iodine and bromine caused the charged particles to become much more mobile within the substance. The scientists thus achieved efficiencies of up to 2.4 percent, which is very high in terms of organic solar cells. Nevertheless, there is still a long way to go before solar cells made out of pentacene can replace the conventional silicon ones, for solar cells on a silicon basis can already reach peak efficiencies of up to 15 percent.