Semiconducting insoluble thin films are prepared by spin-coating soluble molecules then heating the thin film to release the volatile solubility-imparting groups.
Pc and Nc are insoluble so Ono and Okujima added functional groups to the molecules to improve solubility. They then dissolved the molecules in an organic solvent and spun the solution rapidly on glass plate, evaporating the solvent and forming a thin film of the molecules on the glass. When they heated the films, a retro Diels-Alder reaction released the volatile solubility-imparting groups. The final films were totally insoluble and acted as semiconductors.
The group then made an organic field-effect transistor (OFET) using the films. OFETs are essential components of flexible organic electronic displays, which are starting to appear on the market but are hampered by high-cost production.
Tetsuo Okujima says that his work could result in organic electronic devices becoming cheaper and easier to make. 'This is the first example of solution-processed parent Pc- or Nc-based OFETs which are fabricated easily, at low-cost and over a large-area,' he explains.
Jerzy Kanicki, an expert in organic electronics at the University of Michigan, Ann Arbor, US, is impressed by the synthesis. 'This work represents a step forward to realising organic semiconductor-based, low-cost, printable and flexible electronics,' he says. 'From this we can further confirm that the versatility of organic synthetic methods and new soluble precursors allows seemingly infinite flexibility in tuning the electrical properties of OFETs.'