New solar cell sets new efficiency record

German scientists combined two types of absorbers to develop solar cells with a light conversion efficiency of 24%.

The research team of Professor Thomas Riedl at the University of Wuppertal and experts at the Institute of Physical Chemistry of the University of Cologne, the University of Potsdam, the University of Tübingen, the Helmholtz - Zentrum Berlin and the Max-Planck Iron Research Institute, developed developing a dual-panel solar cell that is 24% efficient - measured in terms of the amount of photons converted into electricity.

Solar cells in pairs in a solar simulator at the University of Wuppertal (left) and an energy level meter by optoelectronic spectroscopy at the University of Cologne (right).

This helps the battery to set a world record for highest efficiency with a combination of organic absorbers and perovskite materials. The results of the study were published April 13 in the journal Nature.

Traditional solar cell technologies are mainly based on semiconductor silicon and are considered to have reached the limit of efficiency. This makes it all the more necessary to develop new solar technologies.

In the new study, the team of scientists used a combination of two absorbent materials. The first are organic semiconductors - carbon-based compounds that can conduct electricity under certain conditions. They are paired with perovskite, which is a lead-halogen compound with very good semiconductor properties. Producing both of these requires much less material and energy than traditional silicon batteries.

Sunlight consists of different spectral components, namely colors, so an efficient solar cell must convert as much light into electricity as possible. Experts can do this with solar cells that double. This type of battery incorporates a variety of semiconductor materials, each of which absorbs different bands of the solar spectrum.

In the new study, organic semiconductors were used for visible and ultraviolet light, while perovskite effectively absorbed in the near-infrared region. Similar material combinations have been studied before, but the German team succeeded in significantly increasing the efficiency.

Initially, the world's best organic perovskite batteries were about 20% efficient. The German team of experts increased this efficiency to 24%. "To achieve such high efficiency, it is necessary to minimize the loss at the interface between the materials in the solar cell. To solve this problem, the team at the University of Wuppertal developed a linker that helps connect organic and perovskite materials electronically and optically," said Dr Selina Olthof at the Institute of Physical Chemistry of the University of Cologne.

Specifically, a thin layer of indium oxide is incorporated into the solar cell with a thickness of just 1.5 nanometers to keep the loss as small as possible. Scientists at the University of Cologne played an important role in assessing the energetic and electrical properties of the interface and the interconnection, thereby determining the loss process and optimizing the components. Simulations by a team of experts at the University of Wuppertal show that the new method could create double solar cells with more than 30% efficiency in the future.