A Study on Structure-property Relationships of P3HT-based Conjugated Polymers for Photovoltaic Devices

Download or read book A Study on Structure-property Relationships of P3HT-based Conjugated Polymers for Photovoltaic Devices written by Bobak Gholamkhass and published by . This book was released on 2011 with total page 374 pages. Available in PDF, EPUB and Kindle. Book excerpt: The focus of this research is to investigate structure-property relationships of a series of graft copolymers synthesized using a post-functionalization methodology in which non--conjugated segments are grafted onto a -conjugated polymer, poly(3-hexylthiophene). Taking advantage of the synthetic methodology, electron-acceptor molecules of fullerene are covalently attached to azide-functionalized graft chains grown from the polymer backbone. The goal is to gain knowledge regarding how to control the development of nanostructure morphology in binary blends of photoactive materials used in thin film solar devices. The study was initiated in the context of an increasing interest in nanostructure-molecular assemblies for organic photovoltaics. Post-functionalized poly(3-hexylthiophene) and fullerene (C_60) were employed as the primary materials in the study. Poly(3-hexylthiophene), a benchmark material for organic electronics, is selected as the structure of choice for testing hypotheses, which includes measures to stablilize the morphology of the bulk heterojunction thin films and improve the durability of organic solar cells. In this thesis research, the synthetic approach to obtain a series of donor-acceptor graft copolymers is explored with an emphasis on controlling structural parameters such as graft chain density, length and nature of the functional groups for attaching the fullerene moieties. The research involved detailed synthetic, characterization and morphological studies of these donor- and acceptor-type materials used for solar devices. The individual effects of the several structural parameters that could influence the property systematically investigated. The research outcome demonstrates that performance of a bulk heterojunction solar device is very sensitive to the morphology of the photoactive layer. Specifically, a stable morphology was achieved through a solid state, thermal reaction that initiated covalent attachment of the azide-functionalized graft chains to fullerene, "locking-in" the preformed domains. By purposely locking in the nanostructure, it was shown that stabilization of the morphology enhanced the stability of the solar devices. In addition, a novel device architecture that took advantage of a robust photoactive layer/metallic interface was proposed. The new device architecture in combination with morphology stabilization led to substanial improvements in performance stability. Novel polymeric structures, synthetic advancements and device architecture were the highlights of this research allowing a true study of durability of organic photovoltaic devices.