Vapor deposition rate modifies anisotropic glassy structure of an anthracene-based organic semiconductor

TL;DR

This study demonstrates how varying vapor deposition rate and substrate temperature can control the anisotropic molecular packing and stability of organic semiconductor glasses, with implications for OLED material fabrication.

Contribution

It introduces a deposition rate-substrate temperature superposition principle for controlling molecular order in non-mesogenic organic glasses, extending previous models.

Findings

Deposition rate significantly affects molecular orientation.

Vapor-deposited glasses show higher density and thermal stability.

RTS principle applies to non-mesogenic organic semiconductors.

Abstract

We control the anisotropic molecular packing of vapor-deposited glasses of ABH113, a deuterated anthracene derivative with promise for future OLED materials, by changing the deposition rate and substrate temperature at which they are prepared. We find that, at substrate temperatures from 0.65Tg to 0.92Tg, deposition rate significantly modifies the orientational order in the vapor-deposited glasses as characterized by X-ray scattering and birefringence. Both measures of anisotropic order can be described by a single deposition rate-substrate temperature superposition (RTS). This supports the applicability of the surface equilibration mechanism and generalizes the RTS principle from previous model systems with liquid crystalline order to non-mesogenic organic semiconductors. We find that vapor-deposited glasses of ABH113 have significantly enhanced density and thermal stability compared to their counterparts prepared by liquid-cooling. For organic semiconductors, the results of this study provide an efficient guide for using deposition rate to prepare stable glasses with controlled molecular packing.