X-rays Reveal Details of Plastic Solar Cell Production

Estimated reading time: 3 minutes

Working in cooperation with the Lawrence Berkeley National Laboratory in the USA, Stephan Pröller, doctoral candidate at MSE, used X-rays to make the molecules and their processes visible during the printing of a plastic film. He identified different phases that unfold during the drying of the film.

Initially the solvent evaporates while the other materials stay in solution. This leads to an increase in the concentration of the plastic molecules in the wet film until the electron donor starts crystallizing. At the same time the electron acceptor starts to form aggregates. A fast crystallization process follows, pushing the aggregates of the electron acceptor closer together. At this stage the distance between the interfaces of the two materials is defined, which is closely related to efficiency. To systematically improve the solar cells, this step in the printing process needs to be controlled.

In the last stage optimizing processes within the individual materials are taking place, like the optimization of the packing of the crystals.

"The production speed also plays an important role," explains Pröller. Although this pattern is preserved with faster drying processes, the aggregates and crystals formed by the materials influence the remainder of the structure formation so that slower structure formation has a more positive impact on the final efficiency.

The researchers would now like to use their insights into the processes to gain specific control over the arrangement of the materials using other parameters. These results could then be transferred to industrial production and help to optimize it. 

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