Low-dose electron total scattering analysis resolves non-crystalline phase separation in polymer semiconductors and device multilayers
Author(s)
Pham, Sang T
Sapnik, Adam F
Collins, Sean
Type
Journal Article
Abstract
Nanoscale phase separation in polymer semiconductor blends significantly influences their mechanical, optical, and transport properties, and uncontrolled phase separation ultimately contributes to the long-term degradation of devices. Recent advances in electron microscopy have enabled imaging and diffraction-based analysis of polymer components, but these approaches are typically limited to blends with components exhibiting sharp differences in crystallinity or molecular structure. Here, we employ low-dose scanning electron diffraction to characterize phase-separated domains of components with nearly identical molecular structure, namely poly(9,9-di-n-octylfluorenyl-2,7-diyl) (F8) and poly(9,9-dioctylfluorene-alt-benzothiadiazole) (F8BT). For semicrystalline blends, we demonstrate phase identification and crystallographic texture analysis. In fully amorphous systems with partial phase separation, we highlight the limitations of electron pair distribution function (ePDF) analysis. Instead, we exploit differences in angle-dependent scattering, coupled with calculated intramolecular scattering intensities, to reliably map distinct amorphous phases. Finally, we showcase this suite of techniques for characterizing a model device cross-section, prepared by cryogenic focused ion beam milling. These workflows decouple phase separation and crystallization processes in F8:F8BT blends, provide corroborating insights into F8 crystalline and amorphous intermolecular π − π stacking, and support the direct visualization of non-crystalline organic multilayer interfaces in cross-section needed for failure analysis in organic optoelectronics.
Date Issued
2026-06-08
Date Acceptance
2026-05-05
Citation
Small Methods, 2026, 10 (11)
ISSN
2366-9608
Publisher
Wiley
Journal / Book Title
Small Methods
Volume
10
Issue
11
Copyright Statement
© 2026 The Author(s). Small Methods published by Wiley-VCH GmbH This is an open access article under the terms of the Creative Commons Attribution License, which permits use, distribution and reproduction in any medium, provided the original work is properly cited.
License URL
Identifier
10.1002/smtd.70719
Subjects
amorphous solid
analytical electron microscopy
crystallinity
crystallization
electron diffraction
focused ion beam
materials science
pair distribution function
polymer
semiconducting polymer
Publication Status
Published
Article Number
ARTN e70719
Date Publish Online
2026-05-17