Chlorosomes offer solar energy breakthrough

New research into the development of biologically inspired solar cell devices has shown that chlorosomes, a type of photosynthetic antenna complex, are very good at collecting sunlight and converting it into energy, even if there is little light available and they are in an extreme environment. The structures of light-harvesting complexes such as chlorosomes are central to the electron transfer at semiconductor electrodes in solar devices.

 

Now, a team from Washington University in St. Louis and the Department of Energy's Oak Ridge National Laboratory in the US, have found that chlorosomes are one of the most efficient light-harvesting antenna complexes available in nature, and are able to retain their structures even under extreme conditions. It is hoped that the ability to understand how chlorosomes work could allow researchers to copy their stability and effectiveness for applications involving biohybrid or bio-inspired solar cells and the harvesting of light in synthetic materials.

 

The study, which was led by Robert Blankenship of Washington University and published in the journal Langmuir [Tang et al. Langmuir (2011) doi: 10.1021/la104532b], used small-angle neutron scattering to examine the structure of chlorosomes in green photosynthetic bacteria. The neutron scattering technique allowed them to assess the complex biological systems at a nanoscale level without imposing any damage on the samples involved.

 

The analysis of the neutron experiment, carried out at the High Flux Isotope Reactor in Oak Ridge, provided useful information about how bacteria can be used for solar energy, and examined the structure of the chlorosome under a variety of thermal and ionic conditions. Blankenship, who has been working on photosynthetic systems for over 40 years, and the chlorosome complex from green photosynthetic bacteria for over 30 years, said “We discovered some new behaviors of these complexes to changes in ionic strength, a reversible salt-induced aggregation that was monitored both by dynamic light scattering (DLS) and small-angle neutron scattering (SANS). This must reflect surface charge effects that were not previously appreciated.”

 

Volker Urban, a co-author on the study, also pointed out “What's so amazing about the chlorosome is that this large and complicated assembly is able to capture light effectively across a large area and then funnel the light to the reaction center without losing it along the way”

 

He added “We're trying to find out general principles that are important for capturing, harvesting, and transporting light efficiently and see how nature has solved that.”

 

The team now hope to improve the coupling efficiency of the chlorosome complex to the TiO₂ surface; it is crucial that the complex is able to bind strongly to a surface such as TiO₂, as it allows them to better understand the surface charge properties involved. In addition, the team is also exploring applications of the biohybrid device.