New solar-cell chemistry can make cells more sustainable, say researchers

August 02, 2013 // By Paul Buckley
Researchers at the University of Basel have replaced the rare element iodine in copper-based dye-sensitised solar cells by the more abundant element cobalt to take a step forward in the development of environmentally friendly energy production.

The researchers published their work on Cu-Co cells in the scientific journal Chemical Communications; dye-sensitised solar cells (DSCs) transform light to electricity. The cells consist of a semiconductor on which a dye is anchored. The coloured complex absorbs light and through an electron-transfer process produces electrical current. Electrolytes act as electron transport agents inside the DSCs.
Usually, iodine and iodide serve as an electrolyte. Chemists at the University of Basel have now been able to successfully replace the usual iodine-based electron transport system in copper-based DSCs by a cobalt compound. Tests showed no loss in performance.
The replacement of iodine increases the sustainability of solar cells.  “Iodine is a rare element, only present at a level of 450 parts per billion in the Earth, whereas cobalt is 50 times more abundant,” explained the Project Officer Dr. Biljana Bozic-Weber.
The replacement also removes one of the long-term degradation processes in which copper compounds react with the electrolyte to form copper iodide; long-term stability of DSCs is improved.
The research group supporting the Basel chemistry professors Ed Constable and Catherine Housecroft is currently working on optimising the performance of DSCs based on copper complexes. The group had previously shown in 2012 that the rare element ruthenium in solar cells could be replaced by copper derivatives.
This represents a critical step towards the development of stable iodide-free copper solar cells but the researchres caution that many aspects relating to the efficiency need to be addressed before commercialisation can begin in anything other than niche markets.
“In changing any one component of these solar cells, it is necessary to optimise all other parts as a consequence,” said Ed Constable. This is part of a new approach termed ‘Molecular Systems Engineering’ in which all molecular and material components of a system can be integrated and optimised to approach new levels of sophistication in nanoscale machinery.
The systems chemistry approach is particularly appropriate for the engineering