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
- HZB congratulates Peter Hegemann on winning the Nobel PrizeOur warmest congratulations go to Peter Hegemann, Professor of Neuroscience and Experimental Biophysics at Humboldt University in Berlin. Together with Prof. Georg Nagel (Julius Maximilian University of Würzburg) and Prof. Karl Deisseroth (Stanford University, USA), he has been awarded the 2026 Nobel Prize in Physiology or Medicine. We are delighted for him, his team, Humboldt University and the entire Berlin scientific community.
- Does African Architecture exist?The world’s first Pan-African Architecture Biennale took place this September in Nairobi, Kenya. People from the worlds of architecture, art, academia and politics from 54 African countries and the diaspora had travelled to Nairobi to exchange ideas on traditional and contemporary building methods, materials, experiences and projects. Samira Aden co-organised this biennial as lead curator. We spoke to her about it.
- Nanosilver as an electrocatalyst for CO₂ reductionVia electrolysis, CO2 can be reduced to CO, a raw material for further chemical products such as fuels. Within the GreenQuest Project, an internation team led by HZB chemist Prashanth Menezes has now systematically investigated catalyst layers made of silver nanoparticles, varying both the size of the particles and their density. The best yield was achieved with nanoparticles with diameters of around 10 nm, which were loosely distributed. Furthermore, they demonstrated how the economic efficiency of the electrochemical cell can be enhanced by integrating an additional chemical reaction at the anode, enabling the simultaneous production of a valuable formic acid, hydrogen, and CO in one device.