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Title: Thermal stability of vapor-deposited stable glasses of an organic semiconductor

Vapor-deposited organic glasses can show enhanced kinetic stability relative to liquid-cooled glasses. When such stable glasses of model glassformers are annealed above the glass transition temperature T{sub g}, they lose their thermal stability and transform into the supercooled liquid via constant velocity propagating fronts. In this work, we show that vapor-deposited glasses of an organic semiconductor, N,N′-bis(3-methylphenyl)-N,N′-diphenylbenzidine (TPD), also transform via propagating fronts. Using spectroscopic ellipsometry and a new high-throughput annealing protocol, we measure transformation front velocities for TPD glasses prepared with substrate temperatures (T{sub Substrate}) from 0.63 to 0.96 T{sub g}, at many different annealing temperatures. We observe that the front velocity varies by over an order of magnitude with T{sub Substrate}, while the activation energy remains constant. Using dielectric spectroscopy, we measure the structural relaxation time of supercooled TPD. We find that the mobility of the liquid and the structure of the glass are independent factors in controlling the thermal stability of TPD films. In comparison to model glassformers, the transformation fronts of TPD have similar velocities and a similar dependence on T{sub Substrate}, suggesting universal behavior. These results may aid in designing active layers in organic electronic devices with improved thermal stability.
Authors:
;  [1] ;  [2]
  1. Department of Chemistry, University of Wisconsin—Madison, Madison, Wisconsin 53706 (United States)
  2. Department of Chemistry and Biochemistry, Arizona State University, Tempe, Arizona 85287 (United States)
Publication Date:
OSTI Identifier:
22415617
Resource Type:
Journal Article
Resource Relation:
Journal Name: Journal of Chemical Physics; Journal Volume: 142; Journal Issue: 13; Other Information: (c) 2015 AIP Publishing LLC; Country of input: International Atomic Energy Agency (IAEA)
Country of Publication:
United States
Language:
English
Subject:
37 INORGANIC, ORGANIC, PHYSICAL AND ANALYTICAL CHEMISTRY; ACTIVATION ENERGY; ANNEALING; BENZIDINE; COMPARATIVE EVALUATIONS; DIELECTRIC MATERIALS; ELECTRONIC EQUIPMENT; ELLIPSOMETRY; FILMS; GLASS; LIQUIDS; MOBILITY; ORGANIC SEMICONDUCTORS; RELAXATION TIME; TRANSFORMATIONS; TRANSITION TEMPERATURE; VAPOR DEPOSITED COATINGS