Optimum band gap for hybrid silicon/perovskite tandem solar cell
Sketch of the tandem cell. © H. Cords/HZB
Tandem solar cells based on silicon and perovskites have raised high hopes for future high efficiency solar modules. A team led by perovskite solar cell pioneer Henry Snaith at the University of Oxford has now shown, with contributions by Bernd Rech and Lars Korte of the Helmholtz-Zentrum Berlin, that an ultimate efficiency of 30% should be attainable with such tandem cells. They discovered a structurally stable perovskite composition with its band gap tuned to an optimum value of 1.75 eV. The results have been published in "Science".
Tandem solar cells based on silicon and perovskites have raised high hopes for future high efficiency solar modules (see also results here). A tandem solar cell works by absorbing the high energy photons (visible light) in a top cell which generates a high voltage, and the lower energy photons (Infra red) in a rear cell, which generates a lower voltage. This increases the theoretical maximum efficiency by about 50% in comparison to a standalone silicon cell.
To maximise efficiency, the amount of light absorbed in top cell has to precisely match the light absorbed in the rear cell. However, the band gap of ~1.6eV of the standard perovskite material is too small to fully exploit the efficiency potential of this technology.
A team led by perovskite solar cell pioneer Prof. Henry Snaith FRS at the University of Oxford, in collaboration with silicon solar cell experts Prof. Bernd Rech and Dr. Lars Korte of the Helmholtz-Zentrum Berlin, have shown that an ultimate efficiency of 30% should be attainable with such tandem cells.
They conceived together a tandem cell, in a configuration where the perovskite and the silicon cell are mechanically stacked and contacted separately. The HZB team contributed the silicon cell. The Oxford group did vary systematically the chemical composition of the perovskite layer, and with a precise cocktail of ions discovered a structurally stable perovsksite with its band gap tuned to an optimum value of 1.75 electron volts, maintaining a high electronic quality of the layer. At the same time, they increased the chemical and thermal stability of the material significantly.
Science 8 January 2016: Vol. 351 no. 6269 pp. 151-155
A mixed-cation lead mixed-halide perovskite absorber for tandem solar cells
- Kick-off for a new data and AI centre in BerlinBy establishing a new data and AI centre in Berlin, the Zuse Institute Berlin (ZIB) and the Helmholtz-Zentrum Berlin (HZB) are laying the foundations for a scalable and sovereign data infrastructure in the capital. The project strengthens the scientific capabilities of Berlin’s research community whilst making an important contribution to research security, resilience and technological independence.
- Berlin Battery Lab: BAM, HZB and HU are conducting joint research on sodium batteriesThe Federal Institute for Materials Research and Testing (BAM), the Helmholtz Zentrum Berlin (HZB) and Humboldt-Universität zu Berlin (HU) today officially inaugurated the Berlin Battery Lab (BBL). At this new research platform, BAM, HZB and HU jointly develop and test resource-efficient battery technologies with a focus on sodium-based systems. Together, they develop new materials, investigate innovative cell chemistries, and produce battery prototypes. The research infrastructure of the Berlin Battery Lab is also open to external partners from science and industry and is designed to accelerate the transfer from research to application.
- Humboldt-Fellow at HZB: Alexander R. UhlAlexander R. Uhl, UBC Okanagan School of Engineering in Kelowna, Canada, aims to develop with Roel van de Krol from the HZB Institute for Solar Fuels an efficient and inexpensive photoelectrolyser for producing hydrogen using sunlight. His stay is being funded by the Alexander von Humboldt Foundation.