Researchers at the University of Toronto have developed a technique to greatly improve the efficiency of nano-scale solar panels, or "quantum dots", which can be sprayed onto almost any surface to generate solar power.

To date, solar cells based on this technology have been too inefficient to be practical.

Conventional solar cells are tuned to convert light of only one wavelength into electricity. Quantum dots can be tuned to absorb different parts of the solar spectrum by varying their size. The Toronto researchers have created the first two-layer solar cell made up of light-absorbing nanoparticles. By combining two different types of quantum dots in the solar cell, the researchers have opened the way to making such cells much more efficient. The approach could be used to make triple-layer, or even quadruple layer, cells.

In the Toronto researchers’ cell, one layer of quantum dots is tuned to capture visible light and the other to capture infrared light. They have also introduced a transition layer, made up of four films of different metal oxides, that keeps resistance between the layers low.

The team’s current solar cell has an efficiency of 4.2%. Their goal is to exceed 10% efficiency within five years and keep improving from there. Conventional solar panels are around 15% efficient, but less efficient quantum-dot cells could still be more cost-effective as they could be much  less expensive to manufacture and install.