| About this Abstract |
| Meeting |
2011 Electronic Materials Conference
|
| Symposium
|
2011 Electronic Materials Conference
|
| Presentation Title |
EE2, Following Charge-Trapping Chemical Reactions in Pentacene Films by Selective Chemical Doping and Wavelength-Resolved Electric Force Microscopy |
| Author(s) |
Louisa Brown, Vladimir Pozdin, Justin Luria, Chad Lewis, John Marohn |
| On-Site Speaker (Planned) |
Louisa Brown |
| Abstract Scope |
Despite continued study, the nature of charge traps in pentacene and related polyacenes remains poorly understood. Numerous products of pentacene degradation have been identified in solution, in the solid post sublimation, and in thin films. Which, if any, of these chemical defects is responsible for charge trapping remains unclear. It has been demonstrated in a bulk current-voltage measurement that trapped charge in pentacene can be rapidly cleared under illumination and that the activation energy and prefactor for charge trap formation is consistent with a chemical reaction. Trap clearing rates have recently been measured in a scanned probe microscope experiment as a function of illuminating wavelength to obtain a (localized) trap clearing action <I>spectrum</I> for the first time. In this recent work, a large peak in the pentacene trap-clearing spectrum was observed at an energy well above the peak absorbance of pentacene, which was explained in terms of chemical charge trapping and a new trap-clearing mechanism involving an internal photoexcitation of the charged trap species. Based on quantum-mechanical calculations of the charged trap species’ absorbance spectra, pentacene-6(13<I>H</I>)-one and 6,13-dihydropentacene were identified as likely charge trap precursors. These precursors are proposed to react with pentacene cation radicals to form charged trap molecules. To provide even more definitive evidence that charge trapping in polyacenes is the result of chemical reactions of pentacene cations with chemical defects, we have chemically synthesized two proposed pentacene defect molecules and have developed a method for co-depositing these defect molecules in thin films with pentacene. We have studied these films by electric force microscopy with <I>in situ</I> variable-wavelength illumination. We find that doping with pentacene-6(13<I>H</I>)-one gives a transistor whose localized trap-clearing spectrum is in quantitative agreement with that observed in aged pentacene thin-film transistors. Studies of localized trap-clearing spectra for 6,13-dihydropentacene as a dopant are underway. Our work suggests that acquiring localized trap-clearing spectra and comparing spectra of nascent and intentionally doped films is a powerful approach to identifying the chemical reactions leading to charge-trap formation in polyacene films. |
| Proceedings Inclusion? |
Undecided |