A Cheaper Solar Cell Process Shows Promise

An abundant resource, solar energy represents a possible alternative to burning fossil fuels for human energy consumption. The supply of fossil fuels is shrinking, and their continued use could negatively affect the environment. Dye-sensitized solar cells could be a step toward more cost-effective solar technology, possibly replacing silicon solar cells, which are expensive to manufacture.

Dye-sensitized solar cells imitate the conversion of sunlight into energy in the natural world, as found in plants and light-sensitive bacteria. Annemarie Huijser has improved a process in these cells and has written a doctoral thesis on the subject for Delft University of Technology. It was published in March.

Huijser attempted to partially re-create in solar cells the process she had found in plants. Plants transport excitons, or energy parcels formed on absorption of sunlight, over distances of about 15 to 20 nm to a location where they are converted to chemical energy. The chlorophyll molecules in their leaves are arranged in an efficient sequence for this process.

Huijser focused her research on dye-sensitized solar cells, which comprise a semiconductor, such as titanium dioxide, covered with a layer of dye. The dye absorbs energy from sunlight, which creates excitons that must move to the semiconductor to generate electrical power.

By studying the best sequence of dye molecules, Huijser increased the average distance that the excitons moved within the cell twentyfold, approximately as far as 20 nm. This could lead to a significant increase in the efficiency of solar cells. The mobility of the excitons would have to increase further by a factor of three before the technology could be considered for commercial applications.

The solar cells used in Huijser’s study are closely related to the more well-known Grätzel cells, which have a complicated method of charge transport. Huijser’s approach was to adapt the simple dual-layer system of dye and semiconductor.