An alternative design of a type of solar cell first discovered 20 years ago, the dye-sensitized nanocrystal cell (DSC),  could lead to cheap, printable cells that would massively boost the worldwide use of solar power.

Electrochemist Michael Grätzel at the Swiss Federal Institute of Technology and colleagues have found alternatives to the expensive dyes and voltage limits of the DSC, achieving record-breaking voltages (up to 0.97 V) and efficiencies (up to 12.3%). If efficiency can be pushed up to about 15%, the devices should become cost-effective competitors to silicon photovoltaic cells.

Grätzel devised the dye-sensitized nanocrystal cell in 1991. It uses organic dye molecules to absorb sunlight, the energy of which then kicks electrons onto tiny nanoparticles of the ceramic titanium dioxide (titania) on which the dye sits. These electrons are collected by electrodes to generate an electrical current.

But use of the technology was restricted. The dyes used to harvest sunlight contained atoms of ruthenium, an expensive metal. And because of conversion inefficiencies, DSCs tended to produce only low voltages (less than 0.8 V).

Ref.: Sandra M. Feldt et al., Design of Organic Dyes and Cobalt Polypyridine Redox Mediators for High-Efficiency Dye-Sensitized Solar Cells, J. Am. Chem. Soc., 2010 [DOI: 10.1021/ja1088869]