A Solution-Processable Liquid-Crystalline Semiconductor for Low-Temperature-Annealed Air-Stable N-Channel...

Area of Science:

• Materials Science
• Organic Electronics
• Semiconductor Physics

Background:

• Development of high-performance n-channel organic semiconductors is crucial for advancing organic electronics.
• Organic semiconductors with donor-acceptor-donor (D-A-D) π-conjugation offer tunable electronic properties.
• Liquid-crystalline (LC) properties can influence molecular ordering and charge transport in organic semiconductors.

Purpose of the Study:

• To design, synthesize, and characterize a new solution-processable and air-stable liquid-crystalline n-channel organic semiconductor with a D-A-D π-conjugation.
• To evaluate the performance of the new semiconductor in organic field-effect transistors (OFETs).
• To investigate the impact of alkyl-chain engineering on the optoelectronic and physicochemical properties of D-A-D semiconductors.

Main Methods:

• Synthesis and full characterization of the novel organic semiconductor, α,ω-2OD-TIFDMT.
• Fabrication of top-contact/bottom-gate OFETs using spin-coated thin films of the semiconductor.
• Investigation of liquid-crystalline phase behavior and molecular orientation in thin films.
• Performance evaluation of OFETs, including electron mobility and on/off current ratios, under ambient conditions.

Main Results:

• The new semiconductor, α,ω-2OD-TIFDMT, exhibits a low LUMO energy (-4.19 eV) and a narrow optical bandgap (1.35 eV).
• A hexagonal columnar liquid-crystalline phase was observed over a wide temperature range.
• Spin-coated films showed highly crystalline platelike grains with edge-on molecular orientation.
• OFETs demonstrated high electron mobility (up to 0.11 cm²/Vs) and high on/off ratios (10⁷–10⁸) with excellent ambient stability, representing a 100-fold enhancement over a similar parent semiconductor.
• LC-state annealing was found to reduce electron mobility for transistor-type charge transport.

Conclusions:

• α,ω-2OD-TIFDMT is a promising n-channel semiconductor material for OFETs, particularly for flexible plastic substrates.
• Rational alkyl-chain engineering is an effective strategy to enhance D-A-D π-core coplanarity, solubility, and optoelectronic properties.
• The observed liquid-crystalline properties and molecular ordering significantly impact charge transport characteristics in OFETs.