German researchers have developed a tandem solar panel that achieves 24 percent efficiency. This is measured by the percentage of photons converted to electricity (i.e. electrons). This is the world’s highest-ever combination of organic and perovskite absorbers. Professor Thomas Riedl, from the University of Wuppertal, developed the solar cell with the help of researchers from the Institute of Physical Chemistry in Cologne as well as other project partners from the Universities of Potsdam & Tubingen as Helmholtz-Zentrum Berlin as well as the Max-Planck-Institut fur Eisenforschng. Today’s results were published in Nature with the title “Perovskite/organic tandem sun cells with indium dioxide interconnect”
Conventional solar cell technology is primarily based on semiconductor silicon. Significant improvements in efficiency, i.e. more watts per watt of solar radiation received can be hardly expected. This makes it even more important to develop new solar technologies that are able to make a significant contribution to the energy transition. This work combined two of these alternative absorber materials. Organic semiconductors, which are carbon-based compounds capable of conducting electricity under certain conditions, were used in this work. They were paired with a Perovskite, which is a compound based on lead-halogen compounds and has excellent semiconducting characteristics. These technologies use significantly less material and energy to produce than conventional silicon cells. This makes it possible to make solar cell more sustainable.
Because sunlight has different spectral components (i.e. Solar cells must convert sunlight into electricity as efficiently as possible, as different spectral components of the sun are used. Tandem cells are a combination of different semiconductor materials in a solar cell. Each absorbs different parts of the sun’s spectrum. The organic semiconductors were used in this study to absorb the visible and ultraviolet parts of light. While the perovskite is capable of absorbing the near-infrared, it was not. Similar combinations of materials were explored before, but the current research team was able to significantly increase their performance.
The world’s most efficient perovskite/organic tandem cell had an efficiency of about 20 percent at the beginning of the project. The University of Wuppertal led the Cologne researchers and their other partners in the project to raise this value to 24 percent. Dr. Selina Olthof, from the University of Cologne’s Institute of Physical Chemistry, stated that to achieve such high efficiency the losses at the interfaces of materials within solar cells had been minimized. To solve this problem, the Wuppertal group developed an interconnect that links the organic and perovskite solar cells electronically and optically. Cologne researchers played an important role in the evaluation of the electrical and energetic properties of the interconnect and interfaces. This allowed for the identification and optimization of loss processes. The Wuppertal group demonstrated that tandem cells could achieve an efficiency of over 30% through simulations.