COLL 89 |
| Charge transport at or across interfaces is central to the operation of a wide variety of molecule-based devices, including organic light-emitting diodes, organic thin film transistors (OTFT), and organic photovoltaic cells. In each of these devices, the critical charge transporting interfaces are buried interfaces, which are not readily accessible to conventional structural or spectroscopic probes. Though there have been tremendous advancements in organic semiconductor based devices in the last few years, the difficulty in determining structure-property relationships at buried interfaces has produced a knowledge gap that is a key obstacle to future development. To probe the buried interfaces, we apply attenuated-total-internal-reflection Fourier transform IR and near-IR spectroscopy to directly probe active layers in organic thin film devices fabricated on top of waveguides. When electrical charge is induced in an organic semiconductor by gate-doping, changes in molecular vibrations and low energy electronic transitions are observed; they are attributed to charge carriers inside the active region of the device. This measurement allows the determination of charge carrier identity and density independent of charge transport. Analyzing the rate at which mobile charges fill up and empty out of the active layer of the device allows their mobilities to be quantitatively measured. Examples include quantitative determination of gate-induced n-type doping in OTFT from N-N'dioctyl-3,4,9,10-perylene tetracarboxylic diimide (PTCDI-C8) or –CN substituted PTCDI-C8 and p-type doping and the metal-to-insulator transition in poly-3-hexyl-thiophene (P3HT). |
|
Interfacial Electron Transfer and Solar Energy Conversion: From Molecules to Nanomaterials
8:20 AM-12:00 PM, Monday, April 7, 2008 Morial Convention Center -- Rm. 226, Oral
Division of Colloid & Surface Chemistry |