Integration and modification of photosystem I for bio-photovoltaics

The photosystem I (PSI) from thermophilic cyanobacteria, which is able to harvest light and perform charge separation, was intensively studied in this thesis. It was shown how the PSI protein complex can be immobilized on a surface with the help of two different linker molecules, 2-mercaptoethanol and sodium 3-mercapto-1-propanesulfonate. The two preferential orientations of the PSI protein complexes, downwards and upwards, were determined by successfully employing  single molecule techniques, such as  atomic force microscopy, and combining these with macroscopic techniques such as  sharp metal tips from eutectic Ga/In for both orientation and temperature dependent  conductivity measurements. These experiments allowed to determine the origin of tunnelling current rectification in PSI junctions being induced from the protein dipole moment.

Next, the PSI monolayers were integrated into conventional and inverted bulk heterojunction solar cells, where the dipole properties of the PSI monolayer were measured as a shift of the open-circuit voltage in both devices. Fabricated solely PSI-based solid-state solar cells showed PSI activity and stable functionality in an environment that is very different from the thylakoid membrane. Moreover, the enhancement of PSI functionality was realized by increasing the  PSI light harvesting capabilities at its green gap by simple coupling of artificial chromophores to the protein scaffold. It turned out that 96 dyes per PSI trimer is the best ratio for labelling since it resulted in an four-fold increase in photo activity in solution. Finally, it was proven that PSI modified with many covalently attached organic dyes functions in  a dry state. 

Dissertation: http://hdl.handle.net/11370/1252796a-2903-4dd3-8e8b-8091966caed5