Hybrid solar cell could attain record efficiency of 30%: Helmholtz Scientists realize optimum band gap for silicon/perovskite tandem solar cell

08. January 2016

Hybrid solar cell could attain record efficiency of 30%

Helmholtz Scientists realize optimum band gap for silicon/perovskite tandem solar cell

Schema des Aufbaus der Tandem-Zelle. Das Licht kommt von unten. Bild: Felix Lang/HZB

Sketch of the tandem cell. Light is coming from below. Credit: Felix Lang/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
DOI: 10.1126/science.aad5845

More information:

Helmholtz-Zentrum Berlin für Materialien und Energie
Institute Silicon Photovoltaics

Dr. Lars Korte

Tel.: (030) 8062-41351
Fax: (030) 8062-41333
Email: korte@helmholtz-berlin.de

Prof. Dr. Bernd Rech
Tel.: (030) 8062-41331
Fax: (030) 8062-41333
Email: bernd.rech@helmholtz-berlin.de

Press office:
Dr. Antonia Rötger
Tel.: (030) 8062-43733
Fax: (030) 8062-42998
Email: antonia.roetger@helmholtz-berlin.de

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