Epitaxial thin-film organic semiconductor crystals and devices
Start date: Jan 1, 2013,
End date: Dec 31, 2017
"Today, organic semiconductor devices are severely limited by the strong disorder in the amorphous or polycrystalline semiconductor films. This disorder is in fact due to the nature of the films, and is NOT an intrinsic molecular property. Indeed, single-crystal organic semiconductors are known, and display exciting characteristics and high performance. Unfortunately, they are today only grown as individual objects, not applicable to integrable thin-film transistors (TFT), solar cells (OPV), and light-emitting diodes (OLED) or transistors (OLET).In this project, we propose a radical shift in the film formation of organic semiconductors, to master the nucleation and growth of highly crystalline thin films on arbitrary surfaces. We propose several possible templates for crystal growth, control of nucleation sites and new techniques to impose gradients in supersaturation of the environment from which the molecules condense in a growing crystal. Fundamental understanding of the thin-film crystal forming processes will be acquired by in-situ monitoring, and by modelling of nucleation and growth processes. We will apply similar methodologies to hetero-epitaxy of thin-film crystals, i.e. growth of crystalline layers of different types of molecules, and to doping of crystals. This will open a gateway to use the immense libraries of organic semiconducting molecules for application in high-performance crystalline heterojunction devices.Proof-of-principle devices will complement the materials science study and establish new research domains. We propose integrable crystalline TFTs, as these are also useful to further probe the physics of crystalline organic semiconductors. Crystalline heterojunction OPVs promise combined high exciton diffusion lengths and carrier mobilities. We will explore the benefits of crystallinity in heterojunction OLEDs and OLETs towards higher current densities and brightness, which may lead to the elusive electrically pumped organic laser."
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