Synthesis and Characterisation of New Conjugated Polymers for Solar Cell Applications

Significant efforts were conducted during the last few decades to find a new alternative energy resource that replaces the current conventional resources and reduce emission of greenhouse gasses and Global Warming. The traditional silicon-based inorganic solar cells are efficient but their high cost limits their use. Organic photovoltaic devices offer many features including the low production costs and flexibility of devices. In addition, these materials are commercially available and easy to process compared to inorganic materials. The development of bulk heterojunction photovoltaic devices with high power conversion efficiency is still under investigation. Moreover, enormous numbers of conjugated polymers were synthesised and studied to achieve high power conversion efficiencies by designing conjugated polymers exploiting π-electrons delocalization within the polymer backbone. The solubility of conjugated polymers is an important matter to consider, so attaching alkyl chains to the backbone of the polymer will not only enhance the solubility of these materials but also increase the charge carrier mobility through the increase of molecular weight of conjugated polymer.In this thesis, different studies have discussed the synthesis of donor-acceptor (D-A) conjugated polymers based on benzothiadiazole (BTD) as an acceptor with donor units such as carbazole and fluorene using direct hetero arylation (DHA) polymerisation were undertaken. The synthesis of a series of conjugated polymers based on fluorinated or non-fluorinated BTD units with molecules such as naphthalene, anthracene, pyrene, carbazole, fluorene and bithiophene-based donor units is presented. The impact of fluorine substitution attached to polymer chains has clearly shown deep HOMO levels in the resulting materials, which agrees with findings in the literature. Another aspect was covered in this thesis which is the impact of extending the π-conjugated system by adding additional aromatic units to the polymers backbone. Interestingly, the results from UV-visible and cyclic voltammetry are both satisfying in obtaining low bandgap polymers regardless the type of donor units used in the conjugated polymer prepared.