Novel head-to-tail coupled oligo(3-hexylthiophene) derivatives for photovoltaic applications

Abstract

This thesis contributes to the field of organic solar cells and elucidates novel concepts to increase the power conversion efficiency of this type of photovoltaic device. A main objective of this thesis has been the synthesis and characterization of new dye-derivatized head-to-tail coupled oligo(3-hexylthiophene)s which combine the outstanding hole charge carrier mobilities of the oligothiophene units and the possibility to absorb light in the low energy part of the terrestrial sun spectrum due to the covalently attached dyes. Furthermore, in order to manufacture cost effective organic solar cells it is desirable to substitute the expensive fullerene derivatives in bulk-heterojunction solar cells which in turn makes these novel donor-acceptor materials even more promising candidates due to their inherent property of photoinduced electron transfer. Another goal of this thesis has been the synthesis of novel derivatives of poly(3-hexylthiophene)s which can be employed in heterojunction solar cells consisting of polymer-fullerene blends as the photoactive layers. The incorporation of ethynylene moieties into the polymer backbone significantly lowers the energetic levels of the HOMO by 0.3 eV, resulting in an optimized overlap with the corresponding frontier orbitals of the fullerene acceptor. Furthermore, a new class of compounds based on oligothiophene-derivatized azobenzenes has been synthesized as light switchable molecules which by the application of light at appropriate wavelengths can be interconverted from the trans- to the cis-form and vice versa, making them promising candidates for the construction of self-assembled light-switchable monolayers. In the final chapter of this thesis, new hexabenzocoronene derivatives are disclosed which combine the p-type semiconducting properties of oligo(3-hexylthiophene)s and the capability of hexabenzocoronenes to form self-assembled columnar phases.