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Posted on August 22, 2007 by  & 

Scientific Challenges in Sustainable Energy Technology - DSSC

DSSC photoelectrochemical solar cells that mimic the action of chlorophyll in nature are already being commercialized. They are ten times as efficient as the version met in nature and they are more tolerant of reflected (polarized) light, light at narrow angles of incidence and low levels of light than most alternatives.
An example in production is the ink jet printed flexible film from the G24 Innovations factory in the UK where they utilize the latest breakthrough in material science and nanotechnology creating a new class of advanced solar cells which are the closest mankind has come to replicating nature's photosynthesis. This technology platform will enable a wide range of new products - from those used by consumers every day, such as mobile telephones and laptops, to more cutting-edge products ranging from sensors, water purification and LED lighting systems, portable tent structures and building products.
Despite this advance, the academics across the world feel that DSSC, invented in Switzerland and widely developed and commercialised across Europe, may be far from optimal in design. For example, questions of interest to the Department of Chemistry at California Institute of Technology in the USA currently include:
  • What controls the rate of charge injection from the dye into the semiconductor?
  • What controls the rate of back reaction of injected electrons with oxidized species in the solution?
  • Why is the iodide iodine redox couple the only redox shuttle that works well in these cells?
  • Can the iodide iodine system be replaced by other redox species that would allow more efficient use of the available energy in the photosensitized electrode systems?
  • What controls the rate of electron percolation through the TiO2 film and how do charge carriers "know" to move towards the back electrode as opposed to recombining with the species in the electrolyte?
To address some of these questions, Dr. Nathan Lewis, George L. Argyros Professor of Chemistry, California Institute of Technology says his team is studying a series of Os- and Ru-based metal complexes. This allows them to vary the ground state redox potential, the excited state redox potential, and the electronic coupling to the electrode surface in a systematic fashion. He is investigating the effects that these variations have on the performance of the photoelectrochemical cell.
He says, "We have performed an investigation of how these changes affect the steady-state current vs voltage properties of the cells, and also have performed nanosecond and femtosecond studies of the dynamics of charge injection and recombination at these interfaces. In addition, we are attempting to understand and block the back reaction of electrons in the TiO2 with oxidized species in the electrolyte and to block this reaction through controlled surface functionalization processes. Finally, we are synthesizing a novel series of linked donor-acceptor complexes in an attempt to suppress recombination and to open up the use of other redox couples than iodide iodine and thereby obtain significant improvements in energy conversion efficiency from these types of systems."
A typical DSSC construction
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Posted on: August 22, 2007

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