Surface-induced alignment of pentacene by photo-alignment technology for organic thin film transistors

Abstract

A series of highly soluble maleimide-based polymers with photoreactive pendant group were synthesized and used as a gate dielectric insulator for organic thin film transistors. Photoalignment properties were characterized by UV-visible spectroscopy and the alignment of liquid crystals. Photopolymerization of polymer-coated organic thin film transistors with linearly polarized UV light induces anisotropy in field-effect mobility. The gate dielectric insulator based on the photoalignable maleimide shows higher field-effect mobility and on/off current ratio than those from a SiO 2 gate dielectric insulator with the values of 0.3 cm 2 V 21 s 21 and 10 4 , respectively. Our results demonstrate that the photo-induced anisotropy of alignment films to control the molecular order of semiconducting pentacene is a promising technology for improving the performance of organic thin film transistors.

Morphological Origin of Charge Transport Anisotropy in Aligned Polythiophene Thin Films

“…It is well known that the morphology of organic semiconductor films plays a significant role in dictating their electrical properties. In particular, anisotropic packing of organic semiconductors typically results in anisotropic charge transport properties, as has been demonstrated for a number of organic semiconductor materials . In single crystal small molecule semiconductors such as rubrene, the anisotropy in charge transport can be directly related to the molecular packing structure and subsequent band structure .…”

Anisotropic Structure and Charge Transport in Highly Strain‐Aligned Regioregular Poly(3‐hexylthiophene)

“…Films with high levels of morphological anisotropy show features of charge transport that are difficult to distinguish in semicrystalline polymer films that are azimuthally isotropic (e.g., lacking in‐plane orientation) 2, 3. To obtain aligned conducting polymer films, there has been a range of approaches that include solution processing,3–5 nanostructured confinement,6 embossing,7 rubbed or templated substrates,8–15 direct rubbing of the active film,16–18 directional solidification from a solvent or within a magnetic field,2, 19–21 and stretching or other physical deformation methods 22–30. Here, we employ a method of straining the semicrystalline polymer, poly(3‐hexylthiophene) (P3HT), to align the polymer and gain insight into film morphology and charge‐transport properties.…”

Direct Photoalignment and Optical Patterning of Molecular Thin Films

“…Here, LDSA is applied to produce structured and polarized light emission as applicable for example in polarized organic light emitting diodes (OLEDs). We anticipate LDSA to facilitate the fabrication of organic devices such as transistors with improved charge carrier mobility, vortex retarders, or photonic metasurfaces from active materials …”

“…In polymer films, alignment of polymer chains has been achieved via stretching, polarization selective photocrosslinking/photodissociation, or reorientation due to actuation via photoswitches such as azobenzene . For small molecule systems alignment has been induced by epitaxial growth on single crystals, directional solution processing, alignment layers, and mixed small molecule‐photopolymer systems . However, many of these techniques require additional layers or photosensitive dopants, thereby increasing processing complexity or introducing unwanted impurities.…”