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Systèmes Modèles Donneur-Accepteur pour le Photovoltaïque Organique étudiés par Microscopie à Sonde Locale

Jeudi 25 septembre 2014 14:00 - Duree : 1 heure
Lieu : Amphithéâtre du CNRS bâtiment A, 3ème étage - 25 rue des Martyrs – Grenoble

Orateur : Franz FUCHS (UMR5819 SPrAM CEA-CNRS-UJF)

During this thesis, model donor-acceptor (DA) systems for organic photovoltaics have been studied by non-contact atomic force microscopy (nc-AFM) and Kelvin probe force microscopy (KPFM). To enhance the understanding o f the optoelectronic processes on the nanoscale, DA systems with better defined structural and electronic properties than the one of most bulk heterojunction blends (BHJ), have been studied. With DA phase-separations of below 10nm in organic photovoltaic systems, the highest possible resolution has to be achieved by KPFM to investigate optoelectronic processes. It has been shown that nc-AFM/KPFM measurements in the regime of short range (SR) forces can increase imaging resolution. In preparation of such investigations, the influence of the interaction regime on the topographic measurement via KPFM has been studied for a self-assembly of P3DDT on HOPG. It is demonstrated that imaging in the SR-regime not only increases the lateral resolution, but also assures correct topographic height values. In a next step, DA blends of FG1 :[70]PCMB have been studied by KPFM. For these BHJs, the structure and the scale of the DA phase-separation can be tuned via the liquid crystal behavior of the donor FG1. The in dark potential contrasts are consistent with surface and bulk morphology. The relationship between the surface photovoltage (SPV) and the tip-sample interaction regime has been analyzed. Increased SPV resolutions and image contrasts are obtained in the SR-regime. Furthermore, due to an optical field exaltation caused by the AFM tip, an amplified SPV signal is observed at small tip-sample distances. Finally, a new generation of DA dyads with donor and acceptor moieties has been studied. Its self-assembly on HOPG has been determined via a comparative study by scanning tunneling microscopy and nc-AFM plus molecular mechanics and dynamics simulations. By KPFM the charge carrier generation and collection has been analyzed down to the level of a single molecular layer. A clear relationship between the dyads’ molecular assembly and their photovoltaic properties can be established.

Contact : benjamin.grevin@cea.fr

Discipline évènement : (Physique)
Entité organisatrice : (INAC/SPRAM)
Nature évènement : (Soutenance de thèse)
Site de l'évènement : Polygone scientifique

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