COLL 93 |
| Organic-organic heterojunctions (OOH) are of paramount importance for devices such as multi-layer OLED structures or photovoltaic cells. Their interface energetics control charge transport through, or charge separation in, the device. This talk will review the extensive body of work done on OOH energetics over the past few years via direct and inverse photoemission spectroscopy and Kelvin probe contact potential difference measurements. This work shows three main points. First, although the electronic structure of many OOH interfaces obey vacuum level alignment, substantial interface dipoles (~ 0.2-0.5 eV) are also observed at a significant number of these interfaces.1 Automatic assumption of vacuum level alignment may therefore lead to erroneous OOH energetics. Second, a model based on alignment of the charge neutrality levels of the constituent materials was successfully developed for these weakly interacting, van der Waals-bonded, interfaces. This model was found to provides a quantitative justification for these observations.2 Third, our most recent work shows that the electronic structure of OOHs can be modified when the materials move away from their original intrinsic condition, i.e. by artificially imposing changes in the Fermi level of the substrate via chemical doping or substrate substitution.3,4 This latter point is key to the important issue of OOH engineering. |
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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 |