Towards Harnessing Solar Energy with Iron N-Heterocyclic Carbene Complexes

Abstract

Negative impact of human activity-related emission of greenhouse gases on Earth's ecosphere has been known for decades, but has recently come into spotlight with unprecedented intensity. This is due to increasingly clear understanding that the global warming could soon spiral out of control. It is therefore essential to diminish the use of fossil fuels and switch to renewable energy sources. Despite extensive progress in solar cells technology, it is still very immature and further substantial improvements (lower cost, higher efficiency) are needed in order for it to compete with fossil fuels.The aim of the current study was to advance towards substituting currently dominating ruthenium for cheap and abundant iron as the metal atom in dye-sensitized solar cells (DSSC). The goal was to design, synthesize and characterize a series of iron-based organic complexes with a predefined set of characteristics for potential application as photosensitizers.Chapter 1 describes design and synthesis of a number of compounds, belonging to the homoleptic iron N-heterocyclic carbene family and investigation of their photophysical properties. The desired performance - efficient electron injection - was proven to occur, when one of the compounds was functionalized with an anchoring group and immobilized onto the semiconductor.Chapter 2 details how a series of heteroleptic Fe N-heterocyclic carbene complexes were synthesized and spectroscopically characterized. The production of the corresponding DSSC materials is currently in progress.In chapter 3 the influence of the complex geometry around the metal center is discussed. Higher octahedricity complex demonstrated promising photophysical behaviour, however further optimization is required in order to improve its excited state properties.Chapter 4 deals with tris N-heterocyclic carbene ligands, which were shown to be highly efficient in stabilizing the oxidation state 3+ of the central atom in bis-tridentate Fe complexes. One compound, containing tripodal anionic boron ligand with three N-heterocyclic carbenes was found to be photoluminescent at room temperature with a highest reported to date quantum yield