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