The method developed by scientists from the Technical University of Denmark (DTU) in Roskilde can reliably produce efficient tandem plastic solar cells of many metres in length, as a team around senior researcher Jens W. Andreasen reports in the journal Advanced Energy Materials.
Layered solar cells are the future
The scientists used a production process, where the different layers of a polymer (plastic) solar cell are coated from various solutions onto a flexible substrate. This way, the solar cell can be produced fast and cheap in a roll-to-roll process and in almost any desired length – up to several kilometers long single solar cell modules have already been manufactured. However, the energy harvesting efficiency of this type of solar cell is not very high. To increase the efficiency, a DTU team around Frederik C. Krebs stacked two such solar cells onto each other. Each of these absorbs a different part of the solar spectrum, so that the resulting tandem polymer solar cell converts more of the incoming sunlight into electric energy.
Deep insights with X-ray ptychography
To check shape and function of the protective coating and the other layers of the tandem solar cell, the scientists used the X-ray vision of DESY’s research light source PETRA III that can reveal finest details. At DESY’s experimental station P06, samples only two by four microns in size were being investigated. With the X-ray beam from PETRA III, the researchers could peer into the layer structure in fine detail, using a technique called 3D ptychography. This method reconstructs the three-dimensional shape and chemistry of a sample from the way it diffracts the incoming X-rays. The advantage of ptychography is that it yields a higher resolution than would be possible with conventional X-ray imaging alone. And in contrast to electron microscopy, X-ray ptychography can also look deep inside the sample. The polymer tandem solar cell developed by the scientists converts 2.67 per cent of the incoming sunlight into electric energy.
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