Self-Assembled Chromophores Within Mesoporous Nanocrystalline TiO<SUB>2</SUB>: Towards Biomimetic Solar Cells

Abstract

Artificial light-harvesting antennas consisting of self-assembled chromophores that mimic the natural pigments of photosynthetic bacteria have been inserted into voids induced in porous titania (TiO2, anatase) in order to investigate their suitability for hybrid solar cells. Mesoporous nanocrystalline TiO2 with additional uniform macropores was treated with precursor solutions of the pigment which was then induced to self-assemble within the voids. The chromophores were tailored to combine the self-assembly characteristics of the natural bacteriochlorophylls with the robustness of artificial Zn-porphyrins being stable for prolonged periods even upon heating to over 200 degrees C. They assemble on the TiO2 surface to form nano- to micro-crystalline structures with lengths from tens of nm up to several microm and show a photosensitization effect which is supposed to be dependent on the assembly size. The natural examples of these antennas are found in green sulfur bacteria which are able to use photosynthesis in deep water regions with minute light intensities. The implementation of biomimetic antennas for light harvesting and a better photon management may lead to a rise in efficiency of dye-sensitized solar cells also under low light illumination conditions.

Hierarchal Light-Harvesting Aggregates and Their Potential for Solar Energy Applications

“…In contrast, an amazing 99% of the chlorophyll molecules of plants are devoted to light harvesting, while only 1% participate in electron transfer. If we were to borrow more heavily from nature, then perhaps dye aggregates would be advantageously applied as energy relays that, like the light-harvesting complexes of photosynthetic organisms, funnel energy to the redox-active molecules. There have been some efforts to exploit biomimetic supramolecular assemblies for dye-sensitized solar energy conversion. − Better understanding of the relationship between structural and electronic properties of chromophore aggregates would further the goal of exploiting them to enhance solar photoconversion efficiencies.…”

Biomimetic Dye Aggregate Solar Cells

“…This resulted in a further increase of the photocurrent, even without the treatment in the aqueous TiCl 4 .…”

“…With the term self-assembly commonly a degree of spontaneous ordering is meant, which has a sophisticated growth mechanism or error correction mechanism during the crystal growth, which is often encountered in primitive natural organisms [4]. This may combine a fast growth rate with a low density of defects, due to an error correction mechanism, which effectively inhibits the further growth onto a misplaced unit.…”