Large-Size Single-Crystal Oligothiophene-Based Monolayers for Field-Effect Transistors.

Area of Science:

• Materials Science
• Organic Electronics
• Crystallography

Background:

• High structural quality in organic semiconductors is crucial for superior electrical performance.
• Quasi two-dimensional (2D) organic semiconductor films, particularly monolayers, offer advantages like flexibility and transparency, challenging bulk materials.
• Oligothiophene-based materials are promising for light-emitting applications due to their luminescence and charge-carrier mobility.

Purpose of the Study:

• To demonstrate the growth of single-crystal monolayers of alkyl-substituted thiophene and thiophene-phenylene oligomers with high structural order.
• To investigate the crystallization process and structural properties of these monolayer films.
• To evaluate the electrical performance of these monolayers in organic field-effect transistors.

Main Methods:

• Solution processing techniques (drop-casting, spin-casting) with slow solvent evaporation.
• Grazing-incidence X-ray diffraction/reflectivity (GIXD/R).
• Atomic force microscopy (AFM), differential interference contrast (DIC) microscopy, and imaging spectroscopic ellipsometry.

Main Results:

• Successfully grew large-size (up to 3 mm) single-crystal monolayers with unprecedented structural order.
• Identified the receding gas-solution-substrate contact line as the site for 2D crystallization.
• Monolayers exhibited excellent performance in organic field-effect transistors, comparable to state-of-the-art thiophene-based materials.

Conclusions:

• Simple solution-processing techniques can yield large-size, highly ordered single-crystal organic semiconductor monolayers.
• These monolayers offer competitive electrical performance, rivaling bulk single crystals.
• The findings support the potential of monolayer organic electronics and advanced solution-processing methods.