Inkjet printing of single-crystal films

Abstract

The use of single crystals has been fundamental to the development of semiconductor microelectronics and solid-state science. Whether based on inorganic or organic materials, the devices that show the highest performance rely on single-crystal interfaces, with their nearly perfect translational symmetry and exceptionally high chemical purity. Attention has recently been focused on developing simple ways of producing electronic devices by means of printing technologies. 'Printed electronics' is being explored for the manufacture of large-area and flexible electronic devices by the patterned application of functional inks containing soluble or dispersed semiconducting materials. However, because of the strong self-organizing tendency of the deposited materials, the production of semiconducting thin films of high crystallinity (indispensable for realizing high carrier mobility) may be incompatible with conventional printing processes. Here we develop a method that combines the technique of antisolvent crystallization with inkjet printing to produce organic semiconducting thin films of high crystallinity. Specifically, we show that mixing fine droplets of an antisolvent and a solution of an active semiconducting component within a confined area on an amorphous substrate can trigger the controlled formation of exceptionally uniform single-crystal or polycrystalline thin films that grow at the liquid-air interfaces. Using this approach, we have printed single crystals of the organic semiconductor 2,7-dioctyl[1]benzothieno[3,2-b][1]benzothiophene (C(8)-BTBT) (ref. 15), yielding thin-film transistors with average carrier mobilities as high as 16.4 cm(2) V(-1) s(-1). This printing technique constitutes a major step towards the use of high-performance single-crystal semiconductor devices for large-area and flexible electronics applications.

Small Molecule/Polymer Blend Organic Transistors with Hole Mobility Exceeding 13 cm2 V−1 s−1

“…[1] [3] [4] Over the past few years, this evolution has not only allowed organics to outperform dominant inorganic technologies such as amorphous silicon (aSi), but it has excelled to the point that solution-processed organic transistors have now surpassed the benchmark mobility of 10 cm 2 /Vs, moving OTFTs into the realm of industrial applications. [5] [6] [7] [8] [9] [10] [11] [12] Organic semiconducting blends consisting of a small molecule and a polymerrenowned for their complexity as well as their advantageous electronic qualities -provide one of the most auspicious systems for realising the application of OTFTs in future electronic technologies. [4] [13] [14] Small molecules are well-known for their high charge carrier mobilities due to their high crystallinity, however they are difficult to process from a solution-phase.…”

“…[4] It has been previously shown that C8-BTBT layered crystallinity -which is known to form herringbone structures with lattice constants a = 0.593, b = 0.788 and c = 2.92 -favours hole transport along the film planes (x-y plane). [7] [50] It is therefore important to investigate the crystal structure and quality of the polycrystalline planes parallel to the C8-BTBT:C16IDT-BT:C60F48(1%) film surface, i.e. the charge carrier direction.…”

“…By considering additional processing improvements, we believe that it is feasible for the C8-BTBT:C16IDT-BT:C60F48(1%) transistors to reach hole mobilities close to the maximum value of 31.3 cm 2 /Vs reported for single crystal C8-BTBT based devices. [7] Experimental Section…”

Reversible Optical Control of Conjugated Polymer Solubility with Sub-micrometer Resolution

“…2,3,11,14,28 Unfortunately, none of these methods are universally effective and many require numerous processing steps, reducing the cost advantage of solution-processing. Cross-linking reactions permanently alter the chemical structure and generally require chemical tailoring, which usually results in degraded material properties.…”

Determination of crystal orientation in organic thin films using optical microscopy

“…Polarized light microscopy (PLM) is by far the most popular optical technique for imaging highly-crystalline organic thin films [15,16]. The advantages of PLM are good contrast between different crystal orientations, fast image acquisition, submicrometer lateral resolution and large field of view.…”