Presenter's Name(s)

Yang LiFollow

Primary Faculty Mentor Name

Randall Headrick

Status

Graduate

Student College

College of Arts and Sciences

Program/Major

Materials Science

Primary Research Category

Engineering & Physical Sciences

Presentation Title

Enhancement of charge transfer in thermally-expanded and strain-stabilized TIPS-pentacene thin films

Time

1:00 PM

Location

Chittenden Bank Room

Abstract

We present an extensive study of the optical absorption and electronic properties of TIPS-pentacene thin films utilizing in situ x-ray diffraction, polarized optical spectroscopy and ab initio density functional theory. The influence of molecular packing on the optical and electronic properties are reported for thin films deposited in the temperature range from 25˚C to 140˚C, and for films that are strain-stabilized at their as-deposited lattice spacings after cooling to room temperature. Anisotropic thermal expansion causes neighboring molecules to “slide” relative to each other. This modest change of structure leads to a large blueshift in the optical absorption spectrum as the temperature increases since charge transfer excitations depend sensitively on the nodal structure of the frontier molecular orbitals. This effect is correlated with an enhancement of the field-effect transistor mobility in strain-stabilized thin films. These results suggest a new approach to improve carrier mobility in strained thin films by decreasing the sensitivity to dynamic disorder.

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Enhancement of charge transfer in thermally-expanded and strain-stabilized TIPS-pentacene thin films

We present an extensive study of the optical absorption and electronic properties of TIPS-pentacene thin films utilizing in situ x-ray diffraction, polarized optical spectroscopy and ab initio density functional theory. The influence of molecular packing on the optical and electronic properties are reported for thin films deposited in the temperature range from 25˚C to 140˚C, and for films that are strain-stabilized at their as-deposited lattice spacings after cooling to room temperature. Anisotropic thermal expansion causes neighboring molecules to “slide” relative to each other. This modest change of structure leads to a large blueshift in the optical absorption spectrum as the temperature increases since charge transfer excitations depend sensitively on the nodal structure of the frontier molecular orbitals. This effect is correlated with an enhancement of the field-effect transistor mobility in strain-stabilized thin films. These results suggest a new approach to improve carrier mobility in strained thin films by decreasing the sensitivity to dynamic disorder.