"We can make single crystals in a much simpler way, entirely at room temperature with a £5 artist spray brush."Grigorios Rigas, University of Surrey

Has the time come to replace the silicon traditionally used in electronic devices with printable organic semiconductor inks? Scientists at the University of Surrey in the UK believe so, especially for future electronics that need to be flexible, lightweight, wearable and low-cost.

Single crystal semiconductors, such as silicon, have been at the forefront of scientific interest for more than 70 years, serving as the backbone of electronic devices. These kind of inorganic single crystals are typically grown from a melt at very high temperatures, in special chambers filled with inert gas, using time-consuming and energy intensive processes.

A new class of crystalline materials, called organic semiconductors, can also be grown as single crystals, but in much cheaper, simpler ways, using solution-based methods at room temperature in air. As such, they open up the possibility of large-scale production of inexpensive electronics that could find use in applications ranging from field effect transistors and light emitting diodes to medical x-ray detectors and miniature lasers.

New research, conducted by a team of researchers from the University of Surrey and the UK National Physical Laboratory (NPL) and reported in a paper in Nature Communications, demonstrates for the first time a low-cost, scalable spray-printing process for fabricating high-quality, isolated organic single crystals. The method is suitable for a wide variety of semiconducting small molecules, which can be dissolved in solvents to make semiconducting inks and then be deposited on virtually any substrate.

This process combines the advantages of antisolvent crystallization and solution shearing. The crystals' size, shape and orientation are controlled by the spay angle and distance to the substrate, which also governs the spray droplets' impact on the antisolvent's surface. The resultant crystals are high quality structures, as confirmed by various characterization techniques, including polarized optical and scanning electron microscopy, x-ray diffraction, polarized Raman spectroscopy and field-effect transistor tests.

According to the scientists, this research will have direct impact on printed electronic applications for flexible circuits, advanced photodetector arrays, chemical and biological sensors, robotic skin tensile sensors, x-ray medical detectors, light emitting transistors and diodes, and miniature lasers. "This method is a powerful, new approach for manufacturing organic semiconductor single crystals and controlling their shape and dimensions," said Maxim Shkunov, lead scientist at the University of Surrey’s Advanced Technology Institute (ATI).

"If we look at silicon, it takes almost 1500°C to grow semiconductor grade crystals, while steel spoons will melt at this temperature, and it will fetch a very hefty electric bill for just 1kg of silicon, same as for running a tea kettle for over two days non-stop. And then, you would need to cut and polish those silicon 'boules' into wafers," explained Grigorios Rigas, a PhD researcher at ATI and NPL and first author of the paper.

"We can make single crystals in a much simpler way, entirely at room temperature with a £5 artist spray brush. With a new class of organic semiconductors based on carbon atoms, we can spray-coat organic inks onto anything, and get more or less the right size of crystals for our devices right away."

"The trick is to cover the surface with a non-solvent so that semiconductor molecules float on top and self-assemble into highly ordered crystals," added Shkunov. "We can also beat silicon by using light emitting molecules to make lasers, for example – something you can't do with traditional silicon. This molecular crystals growth method opens amazing capabilities for printable organic electronics."

This story is adapted from material from the University of Surrey, with editorial changes made by Materials Today. The views expressed in this article do not necessarily represent those of Elsevier. Link to original source.