Organic solar cells

Now the use of solar panels has been demonstrated, it can be considered to improve the current concept. The problem with this concept is that the manufacturing of the main raw material of the panels (high-grade pure silicon) is a relatively expensive and energy inefficient process. The hunt for a sustainable replacement has been engaged for a while, though it is only with the recent market growth in solar panels it has got into high gear. The most promising technology is that of the “organic photovoltaic” or organic solar cells. The material could lead to a revolution …

Based on organic solar cells they work differently than ‘normal’ solar cells do. The light absorbed by an organic cell produces so-called ‘excitons’, electrons and holes that can not (as in a standard panel) move independently. Because the electron and the hole are bound together, there can not flow a current. At the interface between two different materials  one exciton can disintegrate into a free electron and a hole corresponding to it. This is an organic cell of the following layers: positive electrode / electron donor (material 1) / electron acceptor (material 2) / negative electrode. When sunlight falls on the material and creates an exciton, the exciton moves to the boundary between the two objects. Here it falls apart into an electron and a hole, the electron moves to the negative electrode and the hole moves to the positive electrode. In short: there’s a current flowing.

The idea of organic thin-film solar cells started in the 70s, when it was discovered that the conductivity of some polymers (with alternating single and double carbon-carbon bonds) greatly increased by subtly contaminate them with other chemicals. Since this discovery was based on these conductive materials used in LEDs and solar cells among others. Organic materials are very diverse, they exist in many properties to adjust so as the ideal material for the job is to become. Organic material is also very flexible in form and can be applied on virtually any surface. Here you can think of thin plastic films or even several layers of paint. Finally, the material is very cheap, comfortable a factor 10-20 cheaper than the current silicon for solar cells.

There are a number of problems. First, energy efficiency, organic solar cells based on a yield of about 3 to 5%, much lower than the 15% of silicon. Part of this low yield is inherent to the technique, excitons can usually move up 3 to 10 nanometers for lifting themselves. The result is actually true that organic solar cells, the thinner the better the chance that the exciton takes the border and can be split. So: the thinner the better. In addition, organic materials are vulnerable to UV radiation (and other high-energy radiation), without UV-filter the organic layer breaks quickly. Finally, another organic material also vulnerable to oxidation, a good protective coating has yet to be invented.

In recent years there have been significant advances made in the lifetime of organic solar cells. There is still much to be done for the technology to become commercially interesting. One thing is certain: the technique is very widely applicable. Consider an energy-generating tent where you can cook, clothes to recharge your mobile, a car that recharges itself and windows that generate electricity. Organic photovoltaic work well in environments namely low light environments, because the material is not reflective and therefore relatively more light absorbent. You see, the possibilities are exciting and diverse. That the revolution is coming is certain, the question is when. These materials are not commonly used when making a solar panel yourself.