Buried layers, hidden treasures
Adlershof’s ingenious strategies of analysis for solar cells and mine deposits
The inside of a solar cell contains areas in which the desired charge transport might be blocked. Prof. Klaus Lips from the Helmholtz-Centre Berlin (HZB), who teaches ”Analytics for Photovoltaics“ at the FU Berlin, calls it a ”buried layer“. ”This is the boundary layer between the lightactive layer, usually made of crystalline silica, and the charge-separating interface,“ says the head of the project Energy Materials In-Situ Laboratory Berlin (EMIL) which the HZB and the Max-Planck-Society (MPG) are involved in. At that point, losses can occur that impair efficiency.
New materials are in demand. Production, for example the growth of the light-active layer, often requires ultrahigh vacuum and highest purity. During the subsequent analysis using X-ray beamlines, for instance in the electron storage ring BESSY II, this is currently not possible. When transferring the sample into the X-ray tube, interfering dust particles or gas molecules cling to it.
This is due to change with EMIL, a worldwide unique sample preparation and analysis laboratory, which will be docked to BESSY II. ”As of 2015, we can transfer the samples directly into the X-ray spectrometer without having to remove them from the ultra-high vacuum,“ says Lips. Processes occurring on the sensitive boundary layers of the photovoltaic modules can thus be analysed already during production. It would also be possible to observe catalysts at work using this method. Private companies will be able to use the facility.
The industry may also be interested in the projects that are currently being coordinated in Adlershof by the Institute for Scientific Instruments (IfG) with substantial support by the Institute for Applied Photonics (IAP). They deal with on-site analysis of metallic materials. These include the rare-earth metals high-tech devices depend on. Whether exploitation is economically viable can only be determined by detailed on-site analysis. Corresponding tests are carried out using mobile X-ray fluorescence spectrometers that are specifically adapted to the requirements of mining. Combining these with X-ray diffractometry would significantly extend their range of application.
The analyses provided by the XRF-mine-spectrometer that is being developed in the context of the MEGA-project are superfast, precise and, what is more, rich in colour. This Xray colour camera shall be able to analyse even minuscule traces of metallic materials. ”The distribution of elements in the sample is displayed in pseudo-colour,“ says Wedell.
By Paul Janositz for Adlershof Special