Effect of Pyrene-Alkyne Donors and the Preparation of a Phenothiazine Literature Record Dye - Synthesis and Evaluation in DSSCs
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- Institutt for kjemi 
The desire to reduce CO2 emissions, combined with an increasing energy demand from the world's increasing population, calls for new environmentally clean energy resources. Solar energy stands out as one of the most viable choices to meet our energy demand. Dye-sensitized solar cells (DSSCs) represent an alternative concept for harvesting solar energy. They are cost efficient, lightweight and have the possibility of application in flexible large-area devices. Further research is needed to improve efficiency, and increase stability. Two phenothiazine based compounds, the novel dye AGZ2 and the record dye AGZ3, were synthesized during this MSc thesis. AGZ2 was prepared to compare its abilities as a photosensitizer in DSSCs to that of dye AGZ1, allowing the effect of an alkyne moiety to be studied. A linear synthesis route of three steps was used to synthesize dye AGZ2. The starting material in this synthesis was the alkylated and formylated phenothiazine backbone, which was brominated using $N$-bromosuccinimide. The target molecule AGZ2 was obtained through a Suzuki cross-coupling followed by a Knoevenagel condensation. To arrive at target molecule AGZ3 an eight-step convergent synthesis was applied. To obtain the aryl triethylene monomethyl ether unit, methyltriglycol was tosylated, followed by a Williamson ether synthesis. Borylation of the aryl ether resulted in the the aryl boronic ester. The first step towards synthesizing the phenothiazine backbone was a Buchwald-Hartwig amination. Four different catalyst systems were tested and Pd2(dba)3/XPhos was selected as the preferred system, due to short reaction times and acceptable yields. A Vilsmeier-Haack formylation of the phenothiazine backbone was performed, followed by a bromination. Finally, target molecule AGZ3 was synthesized through a Suzuki cross-coupling followed by a Knoevenagel condensation. The overall yield of AGZ3 was 17$\%$. As a step towards the total synthesis of AGZ4, with a 2,7-geometry, the Buchwald-Hartwig amination with 2-chlorophenothiazine was studied. Two temperature experiments were designed, and the ideal reaction temperature range to avoid hydrolysis of the product was established. Dye sensitized solar cell devices, using AGZ1, AGZ2, AGZ3 and the reference N719 as dyes, were fabricated and their efficiency measured. Evaluation of the photovoltaic performance of DSSCs, with AGZ1 and AGZ2 as dyes, showed that introduction of an alkyne moiety increased the efficiency with 14%. The results from the photovoltaic studies on the DSSCs with literature record dye AGZ3 contradicted with previously reported results.