The Application of Wide Band Gap Conjugated Polymers in Single Junction Polymer Solar Cells

In this research, a new phenanthroline derivative was synthesized and characterized on purpose to polymerize the monomer via a Stille-polymerization with different electron donating moieties leading to a range of new wide band gap polymers. The novelty in this monomer would be the long side chains in order to ensure the solubility of the entire polymer. Hence there would be no necessity for the donor moiety to have sidechains in order to make the polymer soluble. Beside this phenanthroline synthesis two new benzothiadiazole based wide band gap polymers were synthesized characterized an implemented in photovoltaic devices. These wide band gap polymers are normally used in the front cell of tandem photovoltaic devices, however, in this research the application of wide band gap materials in single junction photovoltaic devices is investigated. Chapter one starts with an outline of the concerns about global warming and climate change. In order to address the consequences of these phenomena, a gradual replacement of the conventional resources by renewable energy resources is necessary. Solar radiation is a free and globally available energy resource and hence solar energy appears to be a good candidate as renewable energy resource. A small history is outlined for photovoltaic devices in general and organic photovoltaic in particular. This chapter also includes the working principle, device layout and characterization methods of organic photovoltaic devices. Chapter two describes the synthesis of a phenanthroline derivative containing decyltetradecyl side chains at the 4 and 7 positions. Three different synthesis routes were performed to synthesize 2,9-dibromo-4,7-di(tricosan-11-yl)dithieno[3,2-c:2',3'-i] [1,10]phenanthroline on purpose to polymerize this monomer afterwards. The purification of this monomer was the drawback leading to the inability of performing a Stille-polymerization. Also a direct(hetero)arylation polymerization did not result in high molecular weight polymers. In order to ease the purification of the phenanthroline derivative, the length of the side chains was reduced to hexyldecyl. The bromination of the hexyldecyl-phenanthroline derivative was unsuccesfull, implying that the length of the side chains is not the bottleneck in this synthesis. Chapter three includes the synthesis of two wide band gap polymers via a Stillepolymerization. The polymers differ in their side chains as one contain octyldodecyl carboxylate side chains (PDCDTBT-OD) and the other polymer is the hexyldecyl analogue (PDCDTBT-HD) Both polymers were characterized and implemented in both conventional and inverted geometry photovoltaic devices. The photovoltaic properties corresponds to the expectations that the devices containing the hexyldecyl derivative in its active layer reaches higher efficiencies with a maximum PCE of 6.2%. However, these results were not reproducible. The photovoltaic devices were optimized for solvent system, thickness and donor:acceptor (D:A) ratio. The best results obtained for the PDCDTBT-OD was a PCE of 4.82% for the photovoltaic devices which were processed from 2% DPE in chloroform in a 1:1.5 donor:acceptor ratio. On the other hand, an efficiency of 6.2% was reached for the PDCDTBT-HD processed from a 1% DIO in chlorobenzene solvent system with a 1:1.5 D:A ratio. The inverted device processed from the same solvent system and donor acceptor ratio resulted in a PCE of 5.26%