Cobalt replacements improve solar cell sustainability

Researchers at the University of Basel in Switzerland have succeeded in replacing the rare element iodine in copper-based dye-sensitized solar cells with the more abundant element cobalt, taking a step forward in the development of environmentally friendly energy production.

Iodine and iodide normally serve as electrolytes. Chemists at the University of Basel successfully replaced the usual iodine-based electron transport system in copper-based dye-sensitized solar cells with a cobalt compound. Tests showed no loss in performance.

The replacement of iodine significantly increases the sustainability of solar cells, according to project officer Biljana Bozic-Weber. "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."

Cobalt also offers a major advantage over iodine by removing one of the long-term degradation processes in which copper compounds react with the electrolyte to form copper iodide and thus improves the long-term stability of dye-sensitized solar cells.

Dye-sensitized solar cells, which transform light to electricity, consist of a semiconductor on which a dye is anchored. The colored complex absorbs light and produces electrical current through an electron transfer process. Electrolytes act as electron transport agents inside the solar cells.

The research group, headed by Basel chemistry professors Ed Constable and Catherine Housecroft, is currently working on optimizing the performance of dye-sensitized solar cells based on copper complexes. They had previously shown in 2012 that the very rare element ruthenium in solar cells could be replaced by copper derivatives.

The breakthrough marks the first report of solar cells that combine copper-based dyes and cobalt electrolytes and thus represents a critical step towards the development of stable iodide-free copper solar cells, according to the researchers.

However, the group points out that many aspects relating to cell efficiency need to be addressed before commercialization can begin in anything other than niche markets.

"In changing any one component of these solar cells, it is necessary to optimize all other parts as a consequence," said Constable.

The group’s findings were detailed in the latest issue of Chemical Communications.