Structural Control over the Self-assembly of pi-conjugated Semiconductors for Advanced Organic Electronic Applications

초록

Recently, it has been shown that the inorganic semiconductor components can be replaced by organic semiconductors capable of achieving reasonably high field-effect mobilities and power conversion efficiencies. These organic semiconductors are inexpensive to synthesize and can be solution-processed in a roll-to-roll fashion with high throughout. In particular, inherently poor polymer properties, such as low exciton diffusion lengths and low mobilities, can be overcome by nanoscale morphology. In the not too distant future, it may be possible to create integrated organic electronics with low-cost processing, flexibility, reliable device stability, etc. We discuss organic semiconductorbased electronics, paying particular attention to structural control of semiconductor films, device design, and potential improvements. The key to developing advanced organic electronics is the establishment of an understanding of the interplay between the various physical scales present. By controlling self-assembled structure of pi-conjugated semiconductors intelligently, we have developed ordered nanostructures showing high charge-carrier transport. As one of present topics, pi-conjugated diblock copolymers with an amorphous (non-conjugated) block have several potential advantages in that they microphase-separate into well-ordered preformed nanostructures. This property significantly improves solubility in most organic solvents. Using poly(3-hexyl thiophene)-block-poly(methyl methacrylate) copolymers, we found that a better solvent for both blocks, which contained both soft and hard segments, produced highly ordered microphase-separated structures during film casting, in contrast with the common nanofibrillar morphologies that formed from toluene. In particular, the controlled alignment of microphase-separated P3HT domains and the characterization of the direction of pi-overlap may be useful in research related to organic field-effect transistors and other organic electronics, such a