Teams at HZB showed perovskite silicon tandem solar cells with an efficiency of about 30% by the end of 2021. In this highly fought area of research, this value held the world record for eight months. The researchers explain how they used reflecting coatings and nanooptical structuring to obtain this record value in the prestigious journal Nature Nanotechnology. Perovskite and silicon tandem solar cells are capable of much better efficiency than silicon solar cells alone. HZB tandem cells have already broken a number of world records. Most recently, in November 2021, HZB research teams used a tandem cell constructed of perovskite and silicon to attain a certified efficiency of 29.8%. For eight months, this unbroken record was the absolute best in the world. This value was not surpassed until the summer of 2022 by a Swiss team at EPFL.
The record-breaking tandem cell was the result of tight collaboration between three HZB teams. The specifics are now presented in Nature Nanotechnology. They were also given the opportunity to summarize their findings and provide a forecast for future developments in a research briefing that was requested by the journal. Prof. Dr. Christiane Becker, who built the world-record cell with the team lead by Dr. Bernd Stannowski (silicon bottom cell) and Prof. Dr. Steve Albrecht, adds that their specialties “quite well compliment each other” (perovskite top cell). A subtly corrugated nanotexture on the silicon surface was incorporated by Becker’s team as a nanooptical structure in the tandem cell. Most surprisingly, Becker notes, “this roughness offers dual benefits at once: it lowers reflection losses and enables a more regular perovskite film development.” In addition, the silicon’s back has a dielectric buffer layer that lessens parasitic absorption at near-infrared wavelengths. The researchers claim that customized nanotextures can aid perowskite semiconductor materials on a variety of levels. These findings are useful for perovskite-based light-emitting diodes as well as tandem solar cells comprised of perovskite and silicon.