A New Class of Solar Cells Based on Stable Protein-Dye Hybrids
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Design and operating principle of the prototype of an MspA-
based “hybrid soft cell” consisting of an (Ru-Diad)8MspA
double layer
adsorbed onto nanosized TiO2.
Credit: Ayomi Perera.
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For decades, the high level of organization in the
photosynthetic process has dazzled researchers. Attempts to incorporate the
light-harvesting proteins involved into functioning devices with long-term
stability, however, have been unsuccessful so far. Now, researchers at Kansas
State University and the University of North Texas have reported the
development of a new kind of photovoltaic device based on the highly stable
protein MspA.
The researchers recognized that the key to functional
protein solar cells was thermal stability, so they relied on mycobacterial
porin MspA. “MspA is an incredibly stable protein, even surviving temperatures
of up to 220°C, and indefinitely stable at room temperature,” explains Stefan
Bossmann, professor of chemistry at Kansas State University. The researchers
capitalized on this knowledge, and in a highly interdisciplinary effort with
Francis D’Souza’s group at the University of North Texas, produced a prototype
solar cell with incident-photon-to-current-conversion efficiencies of up to 1%.
In order to achieve this result, MspA mutants expressing
cysteine residues were produced and linked to eight ruthenium dyes bearing
maleimides via Michael addition reactions. Additionally, MspA self-assembles
into a nanostructured supramolecular complex on titanium dioxide, forcing the
light-harvesting dyes into a well-defined geometry. This type of hierarchical
structure is reminiscent of the protein’s organization in nature.
As reported recently in the Journal of the American Chemical Society, the two
groups then used time-resolved emission measurements to determine that MspA is
capable of supporting electron transfer between the dyes and TiO2.
Lastly, the group produced Grätzel-type Dye-Sensitized Solar Cells and showed
that the ruthenium dye–protein hybrids on TiO2 had a higher
photoconductance compared with ruthenium dyes on TiO2 or MspA on TiO2.
The results are promising for the production of a “greener”
class of solar cells, since the protein component can be harvested from plants,
bacteria, or algae. The protein can be readily isolated from the host organisms
since it is thermally stable and the other proteins are quickly denatured at
higher temperatures. This type of production would be more environmentally
friendly compared with other types of photovoltaics, which generally require
costly amounts of energy or hazardous solvent processing.
Although the device efficiency is fairly modest, the
researchers stress that this is just a prototype. “MspA conducts current, but
not very well, and there are two pathways for improvement. One is introducing
mutations, such as more tryptophane residues, which are better for charge
transport. A more promising pathway utilizes the empty channels in MspA, and
fills them with molecules that are adept at moving charges,” notes Bossmann.
Overall, the incorporation of a stable protein into a
functional device demonstrates the power of biomimicry and offers a promising
new genre of solar cells with greener production. The authors propose that this
new class of photovoltaics be referred to as “hybrid soft” solar cells.
Read the abstract in the Journal of the American Chemical
Society.
Found here http://www.materials360online.com/newsDetails/40404
