Polyfluorinated Naphthalene-bis-hydrazimide for Solution-Grown n-Type Semiconducting Films

Area of Science:

• Materials Science
• Organic Electronics
• Crystallography

Background:

• Naphthalene tetracarboxylic diimides (NDIs) are promising n-type organic semiconductors due to their tunable electronic properties and solution processability.
• Developing stable and efficient n-type organic semiconductors is crucial for flexible electronics and cost-effective device fabrication.

Purpose of the Study:

• To investigate the chemical and environmental stability of NDI-based aromatic hydrazidimides.
• To characterize the thin-film properties and identify new crystalline phases of NDI derivatives.
• To explore the potential for solution-processed, flexible semiconducting films.

Main Methods:

• Spin coating for thin-film preparation.
• Optical microscopy and atomic force microscopy (AFM) for morphology and roughness analysis.
• X-ray diffraction (XRD) in specular and grazing incidence geometry, and X-ray reflectivity for structural characterization.
• 2D Grazing Incidence Wide-Angle X-ray Scattering (GIWAXS) for polymorph identification and structural determination.

Main Results:

• Pentafluorinated NDI derivatives form crystalline, highly oriented, and molecularly flat thin films (roughness = 0.3 nm).
• A novel thin-film polymorph (TF-F5) was discovered and structurally characterized (monoclinic, P2/c).
• The TF-F5 phase forms on diverse substrates (Si, glass, PMMA), indicating substrate-independent formation.
• TF-F5 films show excellent molecular alignment conducive to electron mobility (μ = 0.02 cm²/Vs).
• Polyfluorinated analogues with -CF3 residues did not yield measurable conductivity in thin films.

Conclusions:

• A new, stable thin-film polymorph (TF-F5) of NDI-based hydrazidimides enables the preparation of solution-grown flexible semiconducting films.
• The TF-F5 phase's molecular arrangement is optimized for electron transport, highlighting its potential in organic electronics.
• Understanding structure-property relationships is key to designing high-performance organic semiconductors, with fluorination strategy playing a critical role.