Tandem Solar Cell Demonstrates 29.15% Efficiency

Scientists at Kaunas University of Technology (KTU) have achieved 29.15% efficiency in a solar cell made of perovskite and silicon. This value was certified by the CalLab of the Fraunhofer Institute for Solar Energy Systems. It represents a new world record for a tandem solar element, the KTU researchers said.

To produce the record-breaking cell, the scientists developed a material that self-assembles to form a molecular-thick electrode layer. The self-assembled monolayers (SAMs), which are as thin as 1-2 nm, cover the surface of the solar element. The molecules are based on carbazole head groups with phosphonic acid anchoring groups and are able to form SAMs on various oxides.

The tandem solar cell was realized on a typical laboratory scale of one square centimeter. However, scaling up is possible. Courtesy of Eike Köhnen/HZB.

The researchers integrated a SAM-based perovskite solar cell into a tandem architecture. This resulted in a cell that demonstrated the capability to convert 29.15% of the incident light into electrical energy.

Using traditional technologies, 1 gram (g) of silicon is enough to produce only a couple of square centimeters of a solar element, the researchers said. In contrast, 1 g of the material synthesized by the KTU team is enough to cover up to 1000 square meters (m²) of the element’s surface. In addition, the self-assembling organic material synthesized at KTU is less expensive than the materials currently used in photovoltaic elements. The self-assembling monolayers are formed by a scalable technique and form a strong connection with perovskite material.

Professor Vytautas Getautis, the head of the KTU research group behind the invention. Courtesy of KTU.

“Perovskite-based single-junction and tandem solar cells are the future of solar energy, as they are cheaper and potentially much more efficient,” professor Vytautas Getautis said. “The limits of efficiency of currently commercially used silicon-based solar elements are saturating. Moreover, existing production capacities of silicon solar cells can be used.”

The self-assembling material was applied in the production of a functioning solar cell in collaboration with Helmholtz Zentrum Berlin (HZB) in Germany and the Center for Physical Sciences and Technology in Lithuania. The material, called 2PACz and MeO-2PACz, will soon appear in the market, the KTU researchers said, making further study in labs around the world possible and putting the 30% efficiency mark for solar cells within reach.