Despite ongoing efforts to research, develop and manufacture renewable and environmentally friendly sources of energy, an often overlooked factor is the sustainability of the materials required to produce technologies such as solar cells.
New research from the University of Basel Department of Chemistry, published in Chemical Communications
has suggested one potential solution to the use of prohibitively expensive rare metals - which have previously been chosen for their high efficiency levels - in solar cells.
In their work on dye-sensitised solar cells (DSCs) as part of the team of Professor Ed Constable and Professor Catherine Housecroft, Nik Hostettler and Ewald Schoenhofer have made two principal discoveries.
A DSC is made up of titanium dioxide – a semiconductor – coated in a coloured dye which absorbs sunlight and transmits electrons into the semiconductor. This is what produces the 'photocurrent', the current that flows through a light-sensitive device when it is exposed to radiant power. The researcher's first achievement was to develop a new method for coating titanium dioxide nanoparticles with coloured dyes; a method which involves simultaneously synthesising the dye and attaching it to the semiconductor's surface.
The second significant breakthrough was to show that zinc-based dyes can be used. Although most zinc compounds are colourless, the team discovered in the course of their work that zinc combines with various organic compounds to produce coloured substances. As yet, devices constructed using these dyes are not very efficient, but the low cost of zinc means that the possibility of using them may be well worth further investigation.
Ruthenium, the rare element usually found in DSCs, costs in the region of €2,990 (£2400) per kilogram. It has already been demonstrated that copper can work as a less expensive and more readily available alternative, at around €6.30 (£5.10) per kilogram. However the possibility of using zinc, at a price of only €1.50 (£1.20) per kilogram, could increase the sustainability and availability of DSCs considerably if the efficiency of this type of cell can be improved.
"This is a significant step towards our dream of coupling photovoltaics and lighting in an intelligent curtain which can store solar energy during the day and function as a lighting device at night," commented Professor Constable.