Influence of Molecular Shape on the Thermal Stability and Molecular Orientation of Vapor-Deposited Organic Semiconductors.

High thermal stability and anisotropic molecular orientation enhance the performance of vapor-deposited organic semiconductors, but controlling these properties is a challenge in amorphous materials. To understand the influence of molecular shape on these properties, vapor-deposited glasses of three disk-shaped molecules were prepared. For all three systems, enhanced thermal stability is observed for glasses prepared over a wide range of substrate temperatures and anisotropic molecular orientation is observed at lower substrate temperatures.

Vapor-deposited glasses of methyl-m-toluate: How uniform is stable glass transformation?

AC chip nanocalorimetry is used to characterize vapor-deposited glasses of methyl-m-toluate (MMT). Physical vapor deposition can prepare MMT glasses that have lower heat capacity and significantly higher kinetic stability compared to liquid-cooled glasses. When heated, highly stable MMT glasses transform into the supercooled liquid via propagating fronts.

Orientational anisotropy in simulated vapor-deposited molecular glasses.

Enhanced kinetic stability of vapor-deposited glasses has been established for a variety of glass organic formers. Several recent reports indicate that vapor-deposited glasses can be orientationally anisotropic. In this work, we present results of extensive molecular simulations that mimic a number of features of the experimental vapor deposition process.

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 Tg, 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.

Tunable molecular orientation and elevated thermal stability of vapor-deposited organic semiconductors.

Physical vapor deposition is commonly used to prepare organic glasses that serve as the active layers in light-emitting diodes, photovoltaics, and other devices. Recent work has shown that orienting the molecules in such organic semiconductors can significantly enhance device performance. We apply a high-throughput characterization scheme to investigate the effect of the substrate temperature (Tsubstrate) on glasses of three organic molecules used as semiconductors.