Low-Dose Electron Total Scattering Analysis Resolves Non-Crystalline Phase Separation in Polymer Semiconductors and...

Area of Science:

• Materials Science
• Polymer Science
• Nanotechnology

Background:

• Nanoscale phase separation in polymer semiconductor blends affects device performance and longevity.
• Current electron microscopy methods struggle to analyze blends with similar molecular structures.

Purpose of the Study:

• To develop and apply advanced electron diffraction techniques for characterizing nanoscale phase separation in polymer blends with similar molecular structures.
• To enable detailed analysis of both crystalline and amorphous phase-separated domains.

Main Methods:

• Low-dose scanning electron diffraction
• Crystallographic texture analysis
• Angle-dependent scattering analysis coupled with intramolecular scattering intensities
• Cryogenic focused ion beam milling for sample preparation

Main Results:

• Successfully identified and analyzed phase-separated domains in poly(9,9-di-n-octylfluorenyl-2,7-diyl) (F8) and poly(9,9-dioctylfluorene-alt-benzothiadiazole) (F8BT) blends.
• Demonstrated phase identification and crystallographic texture analysis for semicrystalline blends.
• Developed a novel method using angle-dependent scattering to map distinct amorphous phases, overcoming limitations of ePDF analysis.
• Characterized a model device cross-section, visualizing non-crystalline organic multilayer interfaces.

Conclusions:

• The developed electron diffraction workflows effectively decouple phase separation and crystallization processes in F8:F8BT blends.
• These techniques provide insights into intermolecular π - π stacking in both crystalline and amorphous phases.
• Enables direct visualization of interfaces crucial for failure analysis in organic optoelectronics.