Journal
CHEMISTRY OF MATERIALS
Volume 33, Issue 4, Pages 1455-1461Publisher
AMER CHEMICAL SOC
DOI: 10.1021/acs.chemmater.0c04725
Keywords
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Funding
- Fonds de la Recherche Scientifique (FNRS)
- Fonds voor Wetenschappelijk Onderzoek -Vlanderen (FWO) under EOS project [30489208]
- Austrian Science Fund (FWF) [P30222]
- FNRS [30489208, 2.4565.11, T.0058.14, T.0072.18]
- French Community of Belgian (ARC) [20061]
- Spanish Ministry project GENESIS [PID2019-111682RB-I00]
- Severo Ochoa Programme for the Centers of Excellence in RD (FUNFUTURE) [CEX2019-000917-S]
- Generalitat de Catalunya [2017-SGR-918]
- Spanish Ministry
- Walloon Region (WCS) [1117306]
- Walloon Region (SOLIDYE) [1510602]
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Ph-BTBT-10 is an organic semiconductor with unique performance in thin-film transistors due to its asymmetric shape causing unusual phase behavior. The preparation of thin films involves crystallization from melt, thermal-gradient crystallization, and bar coating at elevated temperatures, with X-ray diffraction revealing unusual peak-broadening effects. A specific type of molecular disorder, induced by crystallization kinetics, is identified and quantified within the thin films, with temperature-dependent experiments showing that defects can be healed by transitioning to a different state at 145 degrees C.
The molecule 2-decyl-7-phenyl-[1]benzothieno[3,2-b][1]benzothiophene (Ph-BTBT-10) is an organic semiconductor with outstanding performance in thin-film transistors. The asymmetric shape of the molecule causes an unusual phase behavior, which is a result of a distinct difference in the molecular arrangement between the head-to-head stacking of the molecules versus head-to-tail stacking. Thin films are prepared at elevated temperatures by crystallization from melt under controlled cooling rates, thermal-gradient crystallization, and bar coating at elevated temperatures. The films are investigated using X-ray diffraction techniques. Unusual peak-broadening effects are found, which cannot be explained using standard models. The modeling of the diffraction patterns with a statistic variation of the molecules reveal that a specific type of molecular disorder is responsible for the observed peak-broadening phenomena: the known head-to-head stacking within the crystalline phase is disturbed by the statistic integration of reversed (or flipped) molecules. It is found that 7-15% of the molecules are integrated in a reversed way, and these fractions are correlated with cooling rates during the sample preparation procedure. Temperature-dependent in situ experiments reveal that the defects can be healed by approaching the transition from the crystalline state to the smectic E state at a temperature of 145 degrees C. This work identifies and quantifies a specific crystalline defect type within thin films of an asymmetric rodlike conjugated molecule, which is caused by the crystallization kinetics.
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