Surface Polarity and Self-Structured Nanogrooves Collaboratively Oriented Molecular Packing for High Crystallinity toward Efficient Charge Transport

Abstract

Efficient charge transport in organic semiconductors is essential for construction of high performance optoelectronic devices. Herein, for the first time, we demonstrate that poly(amic acid) (PAA), a facilely deposited and annealing-free dielectric layer, can tailor the growth of organic semiconductor films with large area and high crystallinity toward efficient charge transport and high mobility in their thin film transistors. Pentacene is used as a model system to demonstrate the concept with mobility up to 30.6 cm V s, comparable to its high quality single crystal devices. The structure of PAA has corrugations with OH groups pointing out of the surface, and the presence of an amide bond further allows adjacent polymer strands to interact via hydrogen bonding, leading to a self-rippled surface perpendicular to the corrugation. On the other hand, the strong polar groups (-COOH/-CONH) of PAA could provide repulsive forces between PAA and pentacene, which results in the vertical orientation of pentacene on the dielectric surface. Indeed, in comparison with its imidized counterpart polyimide (PI), PAA dielectric significantly enhances the film crystallinity, drastically increases the domain size, and decreases the interface trap density, giving rise to superior device performance with high mobility. This concept can be extended to more organic semiconducting systems, e.g., 2,6-diphenylanthracene (DPA), tetracene, copper phthalocyanine (CuPc), and copper hexadecafluorophthalocyanine (FCuPc), demonstrating the general applicability. The results show the importance of combining surface nanogrooves with the strong polarity in orienting the molecular arrangement for high crystallinity toward efficient charge transport in organic semiconductors.

Understanding, Optimizing, and Utilizing Nonideal Transistors Based on Organic or Organic Hybrid Semiconductors

“…In light of the peculiarity, OFETs based on the dielectric modified by triptycene could exhibit exemplary performance compared with the bare dielectric‐based devices in Figure b,c. Beyond the aforementioned interface modification, Hu and coworkers recently utilized a polymer poly(amic acid) with strong polarity and interhydrogen‐bonding functionality to establish a self‐rippled polymer surface with corrugated nanogrooves (Figure d) . The polar carboxylic acid group also offered significant repulsive forces, which can induce the formation of densely packed vertical pentacene layers, facilitating fast carrier transport.…”

“…Copyright 2017, Nature Publishing Group. d) Molecular orientation of pentacene molecules on PAA with different coverages of pentacene (the polymer is shown in blue and the pentacene molecules in red) . e) AFM images of PAA and pentacene on PAA .…”

“…d) Molecular orientation of pentacene molecules on PAA with different coverages of pentacene (the polymer is shown in blue and the pentacene molecules in red) . e) AFM images of PAA and pentacene on PAA . f) Typical transfer curves of the OFET with 20 nm pentacene and device mobility in the saturated region up to 30.6 cm 2 V −1 s −1 .…”

“…f) Typical transfer curves of the OFET with 20 nm pentacene and device mobility in the saturated region up to 30.6 cm 2 V −1 s −1 . Reproduced with permission . Copyright 2017, American Chemical Society.…”

Probing Optical Anisotropy and Polymorph‐Dependent Photoluminescence in [Ln2] Complexes by Hyperspectral Imaging on Single Crystals

“…In this context, crystal packing and molecular arrangement have been recognized as important aspect fort he designo fi nnovative optical devices. [1][2][3][4][5][6][7][8][9][10] Most of these studies focusingo nc orrelations between crystal packing, polymorphism,a nd optical properties are foundw ithin the field of p-conjugated materials foro ptoelectronicd evices, that is, organic light-emitting diodes (OLEDs), organic thin-filmt ransistors, waveguides,r esonators or solar devices.A lternatively, photoluminescent lanthanide (Ln)-based molecules and materials are highly attractive candidates for opto-magnetic applications spanning the broad range from optical sensors, biomedical probesa nd contrast agents to waveguides, and single-molecule magnets, to name af ew. [11][12][13][14][15][16][17][18][19][20][21][22][23] While significant effect of crystal packing on the optical properties of Ln 3 + -based materials has been shown for coordi-nationp olymers and metal-organicframeworks (MOFs), surprisinglyt his has not yet been exploited in molecular species that exhibit polymorphism.…”