To improve solar cell efficiency, Stanford researchers added a self-assembling monolayer (SAM) of an organic molecule to a titanium oxide semiconductor and cadmium sulfide quantum dots.

In the search for cheap and efficient solar cells, Stanford University researchers are mixing in new ingredients.

Chemical engineering professor Stacey Bent on Sunday presented the results of a paper at the annual meeting of the American Association for the Advancement of Science that showed how a new combination of materials boosted the performance of solar cells made with quantum dots.

The research is in very early stages, but it could provide clues on how to make solar cells with relatively inexpensive materials that have higher efficiency than is currently possible.

Many researchers are trying to use materials with quantum dots as a replacement for traditional semiconductors, such as silicon, in a solar cell. Quantum dots are tiny crystals only a few nanometers in size and can be far cheaper to produce than a silicon wafer or thin-film solar cell. Quantum-dot-sensitized solar cells can also be tuned for different wavelengths of light.

But the efficiency of quantum-dot-sensitized solar cells is very low, making them impractical for commercial use. Bent and her research team added an organic molecule to a solar cell using titanium oxide semiconductor and cadmium sulfide quantum dots in an effort to improve the conversion of light to electricity

Although the efficiency is still very low, researchers found that inserting the additional material improved the efficiency threefold. Surprisingly, the size of the organic molecule mattered, but not the type of material, according to Stanford.

When sunlight hits a solar cell, an electron gets excited and "jumps" to another layer of material and carries an electric charge. Bent's theory is that the added layer to quantum-dot-sensitized solar cells helps keep that free electron separated, rather than recombining and losing its energy.