Solution-Processable Indenofluorenes on Polymer Brush Interlayer: Remarkable N-Channel Field-Effect Transistor...

Area of Science:

• Materials Science: Organic semiconductors for electronic applications.
• Chemistry: Synthesis and characterization of novel π-conjugated molecules.
• Physics: Charge transport mechanisms in organic field-effect transistors (OFETs).

Background:

• Solution-processable n-type molecular semiconductors with high electron mobility (μe ≥ 0.5 cm²/ (V·s)), high current modulation (Ion/Ioff ≥ 10⁶-10⁷), and near-zero turn-on voltage (Von) are crucial for organic field-effect transistors (OFETs) but lag behind other semiconductor types.
• Developing such materials requires careful molecular design, control over thin-film morphology, and optimized interfacial properties.

Purpose of the Study:

• To design, synthesize, and characterize a library of solution-processable, low-LUMO indenofluorene-dimalononitrile small molecules (β,β'-C-TIFDMTs) with varied alkyl chain lengths for n-type OFETs.
• To investigate the structure-property relationships, focusing on how alkyl chain length influences solubility, solid-state packing, and thin-film morphology.
• To achieve high electron mobility and performance in ambient conditions through molecular and interface engineering.

Main Methods:

• Synthesis of β,β'-C-TIFDMTs with varying alkyl chain lengths (n=8, 12, 16).
• Physicochemical characterization including solubility and solid-isotropic liquid transition enthalpy measurements.
• Fabrication of OFETs using spin-coating on ultrathin polystyrene-brush surfaces with controlled grafting densities.
• Thin-film characterization using techniques like Raman spectroscopy and microscopic imaging.
• Performance evaluation of OFET devices under ambient conditions.

Main Results:

• A correlation between transition enthalpies and solubility was identified, highlighting the role of alkyl chains in tuning cohesive energetics.
• The C12-substituted semiconductor exhibited superior thin-film crystallization via a 'zipper effect' during thermal annealing, leading to large crystallites with lamellar stacking and favorable in-plane π-interactions.
• OFETs fabricated with C12-TIFDMTs demonstrated excellent n-channel behavior in ambient conditions, achieving electron mobilities (μe) up to ~0.9 cm²/(V·s), current modulation (Ion/Ioff) of ~10⁷-10⁸, and near-zero turn-on voltage (Von ≈ 0 V).

Conclusions:

• The study presents one of the highest-performing solution-processed n-channel OFETs under ambient conditions.
• It elucidates the critical relationships between molecular structure (alkyl chain length), self-assembly, thin-film properties, and device performance.
• The design strategies involving alkyl chain and interface engineering offer a promising route for developing novel high-electron-mobility donor-acceptor π-architectures.