Quantum dots promise to make solar cells more efficient than the current generation. They are also more economical with valuable raw materials, because a layer of only a few dozen atoms thick is enough. For the first time, it has now been possible to baptize quantum dots to make them suitable for solar panels.
Expensive, rare raw materials are still required for the production of solar cells. China is already erecting more and more barriers to the export of strategic minerals such as the so-called rare earths.
Quantum dots more efficient than traditional solar cells
Silicon transistors and silicon solar cells work because they consist of layers of electron-rich (n) and p-materials (with holes). This allows the flow of electrons through the semiconductor to be regulated with voltage: essential for both transistors and solar cells.
In theory it is possible to have what is now happening through a thick layer of semiconductor, also by quantum dots, groups of around a thousand atoms with a diameter of a few nanometers. The theoretical efficiency of this is even greater than that of classical solar cells, because the wavelengths to which quantum dots are sensitive can correspond exactly to those of sunlight, by giving the quantum dots the desired properties and size (1).
Obviously, this would save an enormous amount of raw materials. Quantum dots can also be produced cheaply. Unfortunately, it turned out to be impossible to “dip” quantum dots with atoms that, like n and p materials, produce extra electrons or an electron hole. Phosphorus and boron atoms, which are commonly used, do not function in a quantum dot. Materials at the nanoscale acquire completely different properties, as a result of which the other atoms knock them out of the quantum dot, as it were.
Inexpensive to manufacture
At least: until recently. Israeli researchers Eran Rabani of the University of Tel Aviv and his colleague Prof. Uri Banin of the University of Jerusalem have succeeded in producing separate baptized quantum dots. They start from a solution with silver or copper ions and gradually add this solution to a suspension (fine particles floating in liquid) of crystals of indium arsenide. This resulted in silver doped p-dots or copper doped n-dots.
The nanoparticles are dissolved in a liquid, so could easily be applied by a print head or via a printing press to foldable plastic sheets.
Indium and silver are not cheap at a few hundred euros per kilo, but less than a gram of each is needed per square meter of solar panel because quantum dots are so extremely small. If a working solar panel can be manufactured from this, it means that for a few tens of euros an entire roof can be covered with fully-fledged solar panels.