Single-Crystal-like Structure of Poly(9,9-dioctylfluorene) Thin Films Evaluated by Synchrotron-Sourced Grazing-Incidence X-ray Diffraction

Abstract

ABSTRACT:Detailed structures of friction-transferred poly(9,9-dioctylfluorene) (PFO) thin films have been studied using synchrotron-sourced grazing-incidence X-ray diffraction (GIXD). The results of in-plane GIXD were in full agreement with those of electron diffraction in our previous study. We also revealed the structures of liquid-crystalline (LC) and crystalline films that were prepared by rapid and slow cooling from the LC melted state of the friction-transferred films, respectively. For the crystalline films, the results of in-plane GIXD were not in full agreement with those of electron diffraction; additional weak peaks of the odd 00l reflections were observed only in the GIXD profiles. This implies that the twofold screw symmetry along the c-axis of PFO is broken. The rocking profiles for each reflection gave the order parameter of almost one for the crystalline films and 0.67 for the LC films. These results suggest the ability of friction transfer for obtaining single-crystal-like thin films and the importance of carefully designed annealing process for the applications of the films to various optoelectronic devices.

Oriented Thin Films of Insoluble Polythiophene Prepared by the Friction Transfer Technique

“…The half-width of the distribution of the (110) diffraction plane was estimated to be 4°, which means that the molecular chains are excellently oriented along the friction direction in the film. This distribution of the PT films is comparable to that of PTFE films (about 3°) [ 40 ] and poly(9, 9′-dioctylfluorene) films (about 2–3°) [ 57 ].…”

Investigation and Control of Charge Transport Anisotropy in Highly Oriented Friction-Transferred Polythiophene Thin Films

“…Orientation methods for CPs are generally categorized by the physical state, in which they were processed such as by processing in solution state or in solid state . Solution processing made the device fabrication possible at low cost and low temperature; nonetheless, there are some limitations such as a need for good solubility of the CPs, surface wettability, and, in some techniques, pre-aggregation in solution is essential for orientation. , At the same time, a need for halogenated organic solvents for film fabrication may also create serious health and environmental hazards during large-scale production. , Friction transfer is a solvent-free processing method to orient CPs and is effectively utilized to overcome these issues. − There are reports on the high optical anisotropy of such thin films and their impact on controlling the anisotropic charge transport. − …”

Correlation between Molecular Stereostructure, Film Microstructure, and Electronic Structure of Polyfluorene and Fluorene Based Alternating Copolymers F8BT and PFO–DBT

“…The structural observations of PFO based on TEM and selected area electron diffraction patterns were previously published by Chen et al, Misaki et al, and Brinkmann . GIWAXS diffraction study of PFO structure was published by Misaki et al and Kawana et al Here, the structure of the TA PFO was recorded in grazing-incidence geometry using a 2D X-ray detector. The GIWAXS pattern of TA PFO reveals many diffraction spots suggesting the preferential spatial orientation of the PFO molecular crystals (Figure a).…”