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Title: Nanostructured templates for donor/acceptor interface engineering in organic solar cells
Author: Berhanu, Sarah
ISNI:       0000 0004 2690 9351
Awarding Body: Imperial College London
Current Institution: Imperial College London
Date of Award: 2010
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Organic solar cells have shown promising results as a cheap alternative to inorganic photovoltaic devices. However, they still exhibit low power conversion efficiencies mainly ascribed to short exciton diffusion lengths as well as poor charge transport properties in organic semiconductors. These problems could be solved by controlling the structure of the active layer, which is made of an electron donor and an electron acceptor. Ideally this active layer would show (i) an increased donor/acceptor interface, (ii) a nanostructure that would reduce the distance an exciton needs to diffuse to reach an interface and dissociate and (iii) continuity of each of the donor and acceptor phases in order to provide a continuous pathway to the electrodes for the free charge carriers. However, the formation of such a structure is challenging. In this thesis, a templating strategy using colloidal crystals - 3D ordered nanosphere arrays - has been developed to create an active layer structure aimed at overcoming these issues. Porous donor films and donor/acceptor thin films were grown. The resulting nanocomposites consist of an interpenetrating interconnected donor/acceptor network with a large donor/acceptor interfacial area. Results obtained for films made of copper (II) phthalocyanine tetrasulfonic acid tetrasodium salt (tsCuPc) as the donor material and [6,6]-phenyl-C61-butyric acid methyl ester (PCBM) as the electron acceptor material are presented. The synthesis of monodisperse colloidal polystyrene spheres, the fabrication of colloidal crystals using these spheres and their characterisation by scanning electron microscopy (SEM) and reflectance spectroscopy are first discussed. Then, the growth of tsCuPc porous films and tsCuPc/PCBM nanocomposites is presented and results of material characterisation carried out by Raman spectroscopy and X-Ray diffraction are shown. SEM and pseudo-tomography experiments performed using focused ion beam microscopy provide information on the film 3D nanostructure and network interconnection and confirm that the targeted nanostructure has been fabricated.
Supervisor: De Mello, John ; McComb, David Sponsor: Not available
Qualification Name: Thesis (Ph.D.) Qualification Level: Doctoral