#semiconducting polymers

Stretchable, self-healing and semiconducting polymer films for electronic skin (e-skin)

Next-generation polymers developed in the lab must become stretchable and self-healing to form novel skin-like sensory devices to meet the demands of futuristic electronic skin applications. Although researchers have made notable advances in skin-inspired electronic materials, it is challenging to include desired functions into an active semiconductor for improved sensing. In a new report on Science Advances, Jin Young Oh and an interdisciplinary research team in the departments of Chemical Engineering, Biomedical Research, Electrical Engineering, Materials Science and Mechanical Engineering in the U.S. and South Korea, developed a strain-sensitive, stretchable and autonomous self-healing semiconductor film.

They engineered the new material by blending a polymer semiconductor and self-healing elastomer, dynamically cross-linked using metal coordination bonds. Young Oh et al. controlled the percolation threshold of the polymer semiconductor to form a strain-sensitive film with a gauge factor of 5.75 x 105 at 100 percent strain during stretchable transition. The composite film was highly stretchable with a fracture strain greater than 1300 percent with demonstrated autonomous self-healing at room temperature. The research team then developed an integrated five-by-five stretchable active-matrix transistor sensor array (electronic skin) to detect strain distribution during surface deformation.

New synthesis method opens up possibilities for organic electronics

Semiconducting polymers, large, chain-like molecules made from repeating subunits, are increasingly drawing the attention of researchers because of their potential applications in organic electronic devices. Like most semiconducting materials, semiconducting polymers can be classified as p-type or n-type according to their conducting properties. Although p-type semiconducting polymers have seen dramatic improvements thanks to recent advances, the same cannot be said about their n-type counterparts, whose electron conduction (or 'electron mobility') is still poor.

Unfortunately, high-performance n-type semiconducting polymers are necessary for many green applications, such as in types of solar cells. The main challenges holding back the development of n-type semiconducting polymers are the limited molecular design strategies and synthesis procedures available. Among the existing synthesis methods, DArP (which stands for 'direct arylation polycondensation') has shown promising results for producing n-type semiconducting polymers in an environmentally friendly and efficient way. However, until now, the building blocks (monomers) used in the DArP method were required to have an orienting group in order to produce polymers reliably, and this severely limited the applicability of DArP to make high-performance semiconducting polymers.

Doubling the efficiency of organic electronics

Researchers from Chalmers University of Technology, Sweden, have discovered a simple new tweak that could double the efficiency of organic electronics. OLED-displays, plastic-based solar cells and bioelectronics are just some of the technologies that could benefit from their new discovery, which deals with "double-doped" polymers.

The majority of electronics are based on inorganic semiconductors such as silicon. Crucial to their function is a process called doping, which involves weaving impurities into the semiconductor to enhance its electrical conductivity. This allows various components in solar cells and LED screens to work.

For organic—that is, carbon-based—semiconductors, this doping process is also highly important. Since the discovery of electrically conducting plastics and polymers, a field for which the Nobel Prize was awarded in 2000, research and development of organic electronics has accelerated quickly. OLED-displays are one example already on the market, for example, in the latest generation of smartphones. Other applications have not yet been fully realised, due in part to the fact that organic semiconductors are not yet efficient enough.

Doping in organic semiconductors operates through what is known as a redox reaction. This means that a dopant molecule receives an electron from the semiconductor, increasing the electrical conductivity of the semiconductor. The more dopant molecules that the semiconductor can react with, the higher the conductivity—at least up to a certain limit, after which the conductivity decreases. Currently, the efficiency limit of doped organic semiconductors has been determined by the fact that the dopant molecules could only exchange one electron each.

Electrical enhancement: Engineers speed up electrons in semiconductors

Researchers from the Graduate School of Bio-Applications and Systems Engineering at Tokyo University of Agriculture and Technology (TUAT) have sped up the movement of electrons in organic semiconductor films by two to three orders of magnitude. The speedier electronics could lead to improved solar power and transistor use around the world, according to the scientists. They published their results in the September issue of Macromolecular Chemistry and Physics.

Led by Kenji Ogino, a professor at Graduate School of Bio-Applications and Systems Engineering at TUAT, Japan, the team found that adding polystyrene, commonly known as styrofoam in North America, could enhance the semiconducting polymer by allowing electrons to move from plane to plane quickly. The process, called hole mobility, is how electrons move through an electric field consisting of multiple layers. When a molecule is missing an electron, an electron from a different plane can jump or fall and take its place.

Through various imaging techniques, it's fairly easy to follow the electron trail in the crystal-based structures. In many semiconducting polymers, however, the clean, defined lines of the crystalline skeleton intertwine with a much more difficult-to-define region called the amorphous domain.