The Electrophoretic Deposition of Conjugated Polymer Functionalized Carbon Nanotubes for Photovoltaic Applications

Abstract

<p><p lang="en-US">This experimental research thesis describes the combination of conjugated polymers and carbon nanotubes with the fields of electrophoretic deposition (EPD) and organic solar cells. Prior to these contributions, soluble conjugated polymers and carbon nanotubes that have been functionalized by them had not yet been deposited by EPD from solution or by using non-toxic solvents. Additionally, EPD had not yet been utilized to deposit the active layer in a solid organic photovoltaic device. <p lang="en-US">The EPD of soluble conjugated polymer functionalized carbon nanotubes from non-toxic solvents was achieved through an iterative process of experimentation and technique refinement. The developed EPD technique utilized the high pH region at the cathode substrate to neutralize positively charged weak polyelectrolytes macromolecules. Their functional groups were protonated using a minimized amount of acetic acid which also enabled their solubility. Deprotonation of the quaternary ammonium functional groups rendered them neutrally charged and insoluble tertiary amines. This mechanism facilitated the formation of coatings that were predictable and uniform in appearance and thickness. <p lang="en-US">Control over coating thickness was demonstrated by coatings spanning 100 nm to 10 μm. These coatings were produced by adjusting the applied voltage, solution concentration, and tuning the deposition duration. <p lang="en-US">Techniques for the fabrication of a photovoltaic device using an active layer produced by EPD were established though modifications of general organic photovoltaic device fabrication procedures. These modifications involved redesigning the photolithographic ITO etching pattern, adding an insulating barrier strip, thickening the aluminum electrode layer, and switching the top buffer layer from LiF to BCP.</p>