Quantifying Molecular Disorder in Tri-Isopropyl Silane (TIPS) Pentacene Using Variable Coherence Transmission...

Area of Science:

• Materials Science
• Solid-State Physics
• Crystallography

Background:

• Structural disorder in molecular crystals is a primary obstacle to achieving high charge carrier mobilities.
• Quantifying and understanding the origins of this disorder in organic semiconductors is exceptionally difficult.

Purpose of the Study:

• To develop and apply a novel transmission electron microscopy technique for analyzing structural disorder in molecular films.
• To elucidate the mechanistic origins of disorder in tri-isopropyl silane pentacene films.

Main Methods:

• Utilized variable coherence transmission electron microscopy (VC-TEM).
• Analyzed diffuse scattering patterns, including linear streaks and isotropic background, in pentacene films.
• Differentiated between thermal vibrations and static defects contributing to disorder.

Main Results:

• Identified linear streaks in diffuse scattering attributed to thermal vibrations (amplitude ~0.4 Å) along the pentacene molecular axis.
• Observed a slowly varying, isotropic background linked to static defects (displacement parameter ~1.0 Å) frozen during film deposition.
• Demonstrated that thin film fabrication significantly impacts crystallinity.

Conclusions:

• VC-TEM is an effective method for quantifying disorder in molecular crystals.
• The technique can distinguish between dynamic (thermal) and static disorder contributions.
• This approach provides a valuable tool for comparing and optimizing thin film fabrication processes for improved crystallinity.