Title: Structural Characterization of Vapor-Deposited Glasses of an Organic Hole Transport Material with X-ray Scattering

Abstract

Vapor-deposited organic glasses can be produced with enhanced thermal stability and tunable molecular orientation by controlling the substrate temperature during deposition. Recent work has also shown improved charge carrier mobility associated with anisotropic molecular packing in organic electronics. Here grazing-incidence wide-angle X-ray scattering (GIWAXS) is used to characterize the structural anisotropy in glasses of a hole transport material, N,N'-bis(3-methylphenyl)-N,N'-diphenylbenzidine, commonly referred to as TPD. The TPD glasses were prepared by physical vapor deposition at substrate temperatures between 0.79 T_g and 0.98 T_g, where T_g is the glass transition temperature. A GIWAXS-derived orientation order parameter is used to quantify the anisotropy observed in the scattering patterns of the glasses. The GIWAXS-order parameter exhibits both positive and negative values as a function of substrate temperature, indicating either face-on or edge-on packing, and correlates well with a spectroscopic ellipsometry-derived order parameter that is sensitive to molecular orientation. We propose molecular packing arrangements based on the combination of the two order parameters and explore the relationship between kinetic stability and glass structure.

Authors:

Gujral, Ankit ^[1]; O’Hara, Kathryn A. ^[2]; Toney, Michael F. ^[3]; Chabinyc, Michael L. ^[2]; Ediger, M. D. ^[1]

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+ Show Author Affiliations

1. Department of Chemistry, University of Wisconsin—Madison, Madison, Wisconsin 53706, United States
2. Materials Department and Materials Research Laboratory, University of California Santa Barbara, Santa Barbara, California 93117, United States
3. Stanford Synchrotron Radiation Lightsource, SLAC National Accelerator Laboratory, Menlo Park, California 94025, United States

Publication Date:

Tue Apr 28 00:00:00 EDT 2015

Research Org.:

SLAC National Accelerator Lab., Menlo Park, CA (United States)

Sponsoring Org.:

USDOE Office of Science (SC), Basic Energy Sciences (BES) (SC-22). Materials Sciences & Engineering Division

OSTI Identifier:

1413156

Alternate Identifier(s):

OSTI ID: 1261999

Grant/Contract Number:  

AC02-76SF00515; SC0002161; DMR-1121288; DMR-1410438

Resource Type:

Published Article

Journal Name:

Chemistry of Materials

Additional Journal Information:

Journal Name: Chemistry of Materials Journal Volume: 27 Journal Issue: 9; Journal ID: ISSN 0897-4756

Publisher:

American Chemical Society (ACS)

Country of Publication:

United States

Language:

English

Subject:

36 MATERIALS SCIENCE; molecules; scattering; deposition; amorphous materials; order