Fraunhofer CSP and HTWK Leipzig Develop New Test Method for Photovoltaic Wafers as DIN SPEC

Press Release / 19.6.2017

The Fraunhofer Center for Silicon Photovoltaic CSP has developed a DIN SPEC together with the Leipzig University of Applied Sciences (HTWK Leipzig), regional industry partners and the German Institute for Standardization (DIN) for the strength testing of photovoltaic wafers. The standardized process facilitates quality control in the solar industry.

Biegeversuch Siliziumwafer
© Fraunhofer CSP/Cornelia Dietze
Stephan Schönfelder (left) from the HTWK Leipzig and Felix Kaule from the Fraunhofer CSP observing a 4-point bending test with a polycrystalline silicon wafer.

The DIN SPEC 91351: 2017-04 »Strength Testing for Photovoltaic Wafers«, allows to carry out a uniform strength test of 120 to 220 μm thin silicon plates, so-called wafers, for photovoltaic cells and modules. In this case, a standardized bending test is used to determine at which force effect a wafer of crystalline silicon breaks. The test is necessary because the brittle material is very susceptible to breakage and therefore must not be exposed to high mechanical loads during the production process. The DIN SPEC defines how this bending test must be constructed, carried out and evaluated. It is internationally the first standard specification in this field. For the users of the standard, complex non-linear problems are made available in charts and tables, which considerably facilitates communication across the value chain in solar cell production.

The working group for the DIN SPEC was led by Felix Kaule at Fraunhofer CSP and co-operated closely with Stephan Schönfelder, professor for the simulation of energetic and technical systems at HTWK Leipzig. The two research facilities have been working together for many years in the field of mechanics and finite element simulation and have gained new insights into the theoretical and material-mechanical interactions for brittle materials as well as valuable competences for the strength measurement of brittle silicon wafers.

»I am very pleased that the experience gained from our intensive cooperation and many thousands of broken wafers now enables a standard specification. Due to the optimization potential of the associated analysis and production processes, the DIN SPEC, that is now available, is very interesting for all industrial companies in the field of photovoltaics,« says Schönfelder.

»So far, the deformation behavior of the wafers has always had to be complexly simulated. This is because wafers do not deform linearly under load. By means of conversion tables in the DIN SPEC, anyone can now reliably evaluate the strength of silicon wafers without simulation models,« says Felix Kaule of Fraunhofer CSP.

The DIN SPEC is used to publish international standards and can be the basis for a DIN standard.