Scientists from DTU Energy at the Technical University of Denmark have in collaboration with researchers from the Paul Scherrer Institute (PSI) in Switzerland exploited the unique capability of non-destructive three-dimensional imaging with nanometer resolution to make a 3D tomographic reconstruction of an organic solar cell.
Polymer solar cells are in the spotlight as a candidate for the sustainable energy production of the future. Among the challenges to realize this, their production needs to become efficient and reliable while avoiding the use of chemicals which are harmful for the environment. Because the relevant structures in solar cell devices are as small as a few tens of nanometers or, equivalently, a thousand times smaller than a human hair, their visualization without destroying the entire layered structure of the device remains a challenge even for the most advanced imaging techniques using electron microscopy. Yet this characterization is crucial for identifying the failure mechanisms in developing mass production of environmentally friendly organic solar cells.
Scientists from DTU Energy at the Technical University of Denmark have in collaboration with researchers from the Paul Scherrer Institute (PSI) exploited the unique capability of non-destructive three-dimensional imaging with nanometer resolution. They did it by using the large Synchrotron light research facility called Swiss Light Source to visualize a complete tandem solar cell device including layers coated from solutions of nanoparticles in water that convert solar energy to electricity.
“We used a newly developed method that made it possible to test an entire solar cell stack with very high resolution. The method was not our invention, but we've used it on a solar cell made of materials that have never been tested in this way before”, explains senior researcher at DTU Energy, Jens Wenzel Andreasen.
"We used a newly developed method that made it possible to test an entire solar cell stack with very high resolution"
Jens Wenzel Andreasen, senior researcher at DTU Energy
By analyzing the resulting three-dimensional images, the failure mechanism of the water based solar cells was identified and improved performance was demonstrated by alternative fabrication routes.
“We were able to increase the voltage from at 0.5 to 1 V, thereby showing that both solar cell layers work, where as a starting point one layer was short-circuited. This is not THE solution for water-based tandem solar cells, but part of the reason why they did not work as they should”, explains Jens Wenzel Andreasen.
The researchers of DTU and PSI found that to make nanoparticle active layers a viable alternative to bulk heterojunctions, the coatability of the active nanoparticles need to be improved.
Their conclusion was – to quote the researchers’ recent paper – “By top coating conducting polymer on the nanoparticle layer, we demonstrate that tandem potentials above 1 V can be achieved when the nanoparticle layers’ structural flaws, i.e. porosity and roughness, are reduced. We conjecture that the structure of the nanoparticle layer can be improved either through polar surface modifications, heating steps or by reduction of the net charge on the particles, for instance by the use of non-ionic surfactants.”
3D rendering of the tomographic reconstruction of a fragment of an organic solar cell. The different layers involved in the functioning device have been virtually cropped at different positions to facilitate their visualization.
Figure courtesy of Emil Pedersen/DTU Energy.