A German research team has developed a tandem solar cell with a photoelectric conversion efficiency of 24%. This sets a new world record for the highest efficiency ever achieved with this combination of organic and peroxide-based absorbers.
The solar cell was developed by the group of Prof. Thomas Riedel at the University of Wuppertal together with researchers from the Institute of Physical Chemistry at the University of Cologne, other project partners at the Universities of Potsdam and Tübingen, as well as the Helmholtz Center Berlin and Düsseldorf Co-developed with the Max Planck Institute for Essen-Foss.
Traditional solar cell technology, mainly based on the semiconductor silicon, is now considered to have "reached a bottleneck". It is therefore difficult to make further improvements in photoelectric conversion efficiency (ie, collecting more watts of electricity per watt of solar radiation). This makes it all the more necessary for us to develop new solar technologies that will make a decisive contribution to the energy transition.
In this work, two such alternative absorber materials were combined. Here organic semiconductors are used, which are carbon-based compounds that can conduct electricity under certain conditions. These materials are paired with a lead-halide-based peroxide that has excellent semiconducting properties. Both technologies require far less material and energy to produce than conventional silicon cells, making solar cells more sustainable.
At the start of the project, the world's best peroxide/organic tandem cells were around 20 percent efficient. Led by the University of Wuppertal, the Cologne researchers, together with other project partners, were able to increase this figure to an unprecedented 24%.
"In order to achieve such high efficiencies, interfacial losses between materials within a solar cell must be minimized," says Dr. Selina Olthof from the Institute of Physical Chemistry at the University of Cologne. To solve this problem, Wuppertal's research group developed a so-called interconnect that electronically and optically connects organic and peroxide sub-cells.
As an interconnect, a thin layer of indium oxide is integrated into the solar cell with a thickness of just 1.5 nanometers to keep losses as low as possible. Researchers in Cologne played a key role in evaluating the energetic and electrical properties of interfaces and interconnects to identify loss processes and further optimize components. Simulations by the Wuppertal research group show that with this approach, tandem cells with efficiencies in excess of 30% can be realized in the future.
