Molecular tweak boosts efficiency of natural semiconductors for versatile digital units

(Nanowerk News) Adding a easy, sulfur-containing chemical group to a semiconducting molecule can dramatically enhance the molecule’s efficiency in a transistor, RIKEN chemists have discovered (Advanced Materials, ““Manipulation” of crystal structure by methylthiolation enabling ultrahigh mobility in a pyrene-based molecular semiconductor”). This means that the properties of carbon-based semiconductors could possibly be tuned by incorporating these teams. Most digital units are at present based mostly on silicon. However, natural semiconductor molecules provide a technique to make cheaper, versatile units akin to show screens, wearable sensors and disposable radio-frequency identification tags. But most natural semiconductors can’t but match the efficiency of their silicon rivals. Two benchmark natural semiconductors are pentacene and its by-product TIPS-pentacene. They include electrons that smear out throughout the molecules, forming the so-called p-conjugated system, which aids the transport {of electrical} cost. In pentacene crystals, the molecules are organized in a herringbone sample, a standard construction for natural semiconductors. When these herringbone patterns type a sandwich-like construction, the cost transport could be very poor. In distinction, TIPS-pentacene molecules have a extra uncommon sample—stacking like bricks in a wall. This shapes the molecules’ p-conjugation in a approach that improves cost transport and reduces the impression of imperfections within the crystal. However, it has been tough to make sure that new natural semiconductors undertake the brickwork construction. Now, Kazuo Takimiya of the RIKEN Center for Emergent Matter Science and his colleagues have discovered that including methylthio teams (CH3S–) to natural semiconductors may help molecules to type this helpful sample. Optical microscopy photos of a single crystal of MT-pyrene (gold trapezoid). It boosted the efficiency of a field-effect transistor. (Image: RIKEN Center for Emergent Matter Science) The researchers examined their strategy on a molecule known as pyrene, modifying every molecule with both two or 4 methylthio teams. Pyrene itself has a sandwich herringbone construction, however the compound carrying 4 methylthio teams, known as MT-pyrene, had a brickwork construction. The workforce then grew 50–150 nanometer-thick plates of crystalline MT-pyrene and used them to provide 26 field-effect transistors. The units all carried out properly, exhibiting one of many highest recorded cost mobilities for any natural semiconductor with the brickwork construction. The researchers discovered that when every molecule had 4 methylthio teams, they disrupted sure interactions between neighboring molecules. This prevented them from forming a sandwich herringbone construction, and ensured that they might solely stack face-to-face, like bricks. This optimized the interactions between p-electrons and in the end enhanced cost transport. The workforce is assured that this technique may be prolonged to different natural molecules. “We think that methylthiolation is a promising approach that can be applied to many other organic semiconductors,” says Takimiya. The workforce plans to evaluate how different easy chemical teams have an effect on the crystal constructions of supplies. They additionally hope to develop easier strategies to provide bigger quantities of such crystals.