Electroluminescent displays, lighting (organic light-emitting diodes (OLED), circuits on flexible substrates, and photovoltaic cells are all applications of organic electronics that rely on industrial organic semiconductors (OSC).
Due to a fundamental lack of the understanding of how molecular structure and supramolecular organization affects optoelectronic properties Prof. Yves Henri Geerts and his colleagues at Université Libre de Bruxelles have undertaken a study of single crystal thin films of Terthiophene by directional crystallization by means of a thermal gradient using the Linkam GS350 stage.
Optoelectronic properties can also be affected by the method of fabrication, therefore determining a method to control deposition and crystallisation is important.
As part of his research Prof. Yves Henri Geerts used polarized optical microscopy (POM) and X-ray diffraction to characterise the shape, size, and orientation (in and out of the plane of the substrate) of the crystals produced by the thermal gradient technique.
A sample of Terthiophene was placed on a cover slip on the hot side of the stage and is slowly translated to the cold side at a constant speed until all the sample is on the cold side.
One side is above the melting temperature (hot side) and the other at a temperature below the crystallization temperature (cold side).
The conclusion of the experiment was that temperature gradients could potentially be used to control crystal growth and these conditions induce a preferential fast growth direction perpendicular to the gradient direction. In addition it is found that nucleation and growth can be decoupled for OSC crystallizing from the melt in a temperature gradient and that these conditions lead to the generation of highly textured thin films with uniaxial in-plane orientation of crystallites.
By Caroline Feltham