Organic photovoltaic technologies are one of the most sustainable and economical alternatives to traditional silicon-based solar technologies. At present, however, organic and dye-sensitized solar cells convert light into electricity with less efficiency than traditional thin-film cells. A solution comes from multijunction solar cells that can overcome the fundamental efficiency limits of single-junction devices.
A German research team has developed a perovskite-organic tandem solar cell that reaches 24% efficiency – measured according to the fraction of photons converted into electricity. According to the researchers, this set a new world record as the highest efficiency achieved so far with this combination of organic and perovskite-based absorbers.
The perovskite-organic tandem solar cell was developed by Professor Dr. Thomas Riedl’s group at the University of Wuppertal, together with researchers from the Institute of Physical Chemistry at the University of Cologne and other project partners.
At the start of the project, the world’s best perovskite-organic tandem cells had an efficiency of around 20%. The research team was able to increase this value to an unprecedented 24%.
“To achieve such high efficiency, the losses at the interfaces between the materials within the solar cells had to be minimized,” said Dr. Selina Olthof of the University of Cologne’s Institute of Physical Chemistry. “To solve this problem, the group in Wuppertal developed a so-called interconnect that couples the organic sub-cell and the perovskite sub-cell electronically and optically.”
To keep losses as low as possible, a thin layer of indium oxide was integrated as interconnect in the solar cell with a thickness of merely 1.5 nanometres. The researchers assess the energetic and electrical properties of the interfaces, and the interconnect in order to identify loss processes and further optimize the components.
The group’s simulations showed that tandem cells with an efficiency of more than 30% could be achieved in the future with this approach. Scientists from the Universities of Potsdam and Tübingen as well as the Helmholtz-Zentrum Berlin and the Max-Planck-Institut für Eisenforschng in Düsseldorf also took part in the project.