Walter Schottky Institute
Center for Nanotechnology and Nanomaterials

Welcome to the Brandt group
Group leader: Prof. Dr. Martin Brandt

Home Donors as qubits Decoherence in QDs Silicon solar cells Ferromagnetic semiconductors Surface functionalization Doping in Si nanocrystals Black Silicon surfaces Sheet polymers

Black Silicon surfaces

Light is reflected whenever it passes from one material to another. This also happens when light enters a solar cell. The reflection can be minimized by using anti-reflection coatings such as those often found on glasses/spectacles. On crystalline Silicon, this anti-reflection coating usually consists of a thin layer of SiN3. It is optimized to suppress reflection of red light and does not work as well in the blue, which accounts for the slightly bluish color exhibited by most multicrystalline Si solar cells.

Brandt 16 We have developed a new method to structure the surface of Si-based solar cells so that it transmits light with minimal reflection losses over the whole useful spectral range. The technique is based on the local catalytic action of nanometer-sized Au dots when the surface coated with them is exposed to a particular etching solution. The result is a nanostructured surface where the refractive index gradually changes from that of air to that of Si. If this happens on a length scale smaller than the wavelength of light, its reflection is suppressed.

The technique works on all different kinds of Si-based solar cells, including single- and multicrystalline cells as well as cells made from hydrogenated amorphous Silicon. In addition to a reduction of the reflection losses, the nanotextured surfaces lead to the trapping of light, which allows the solar cells to be thinner than those with conventional anti-reflection coatings, resulting in a significant cost reduction.

Selected publications

  • Black nonreflecting silicon surfaces for solar cells
    Applied Physics Letters 88 203107 (2006)
    S. Koynov, M. S. Brandt, M. Stutzmann

  • Black multi-crystalline silicon solar cells
    physica status solidi-rapid research letters 1 R53 (2007)
    S. Koynov, M. S. Brandt, M. Stutzmann

Walter Schottky Institut About the Institute Research

Technische Universität München Annual Reports Photonics & Optoelectronics
Am Coulombwall 4 Events and News Quantum Technologies
D-85748 Garching History of WSI Energy Materials
Germany How to get to WSI Engineered Nanomaterials
Scientific Background Functional Interfaces
Tel: +49-(0)89-289-12761 Seminars Nanofabrication
Fax: +49-(0)89-289-12737 The WSI in Numbers

Partners Publications
(c) 2018 Walter Schottky Institut WSI Association


Walter Schottky Institut Navigation

Technische Universität München Contact
Am Coulombwall 4 Groups
D-85748 Garching Institute
Germany Partners
Tel: +49-(0)89-289-12761 Research
Fax: +49-(0)89-289-12737 Groups
(c) 2018 Walter Schottky Institut