Iron-Based Dye-Sensitized Solar Cells - From Theory to Working Solar Cell

Abstract: In the hunt for fossile-free energy-harvesting techniques, solar cells constitute one of the most promising techniques. Today, silicon-based solar cells are the dominant technique on the market but even the Silicon solar cell has limitations which means that there is a motivation for developing new solutions. One of those techniques is the dye-sensitized solar cell. Just as in photosynthesis, the solar cell contains a dye molecule that when absorbing the light from the sun can separate an electron from an electron hole. The electron is injected into titania and from there extracted as current. In this Master's thesis, two new dye molecules called FeCAB26 and FeCABCN2 have been investigated by spectroscopic methods (absorption spectroscopy, emission spectroscopy and transient absorption spectroscopy), quantum-chemical calculations and electrical measurements with the purpose to investigate the potential for usage as sensitizers in dye-sensitized solar cells. The molecules are iron-carbene-complexes, synthesized by colleges at Lund University, which are at the frontier of this research field since many traditionally used sensitizers have been ruthenium-complexes. Both molecules were able to sensitize films of titania and absorb light in the visible part of the spectrum. Quantum-chemical calculations indicated that the molecules did excite an electron from metal-centred orbitals to ligand-centred orbitals upon absorption of light. The molecules did also inject electrons into titania via the excited metal-to-ligand charge transfer state. The excited states had lifetimes of 21 ps and 36 ps for the different molecules. When the dye molecules were used as sensitizers in solar cells, a photocurrent was measured upon illumination in a solar simulator for the molecule FeCABCN2. Without having optimized the fabrication process, the efficiency of the best solar cell was 0.13 %. This shows a proof of concept that FeCABCN2 could work as a sensitizer in DSSCs. The optical characterization of both molecules will contribute to the development of iron-carbene-complexes as dye molecules to be used for applications in a broader context than just solar cells.