When photovoltaic modules are exposed to high system voltages with crystalline silicon solar cells and are operated in a humid environment, power losses can occur. This disturbance is called potential-induced degradation (PID), it can lead to the complete failure of affected modules.

Volker Naumann and his team succeeded in elucidating the physical basis of the PID and transforming this process into a model. Investigations on the microstructure plane show that crystal defects in the silicon generate shunts and are responsible for PID. These crystal defects are called stack defects and have lengths of only a few micrometers and a thickness of only one atomic layer. Short circuits are caused by the penetration of sodium atoms into the silicon of the photovoltaic cell.

Based on these findings, Fraunhofer CSP, together with Freiberg Instruments, developed a test device that measures the susceptibility of solar cells to this effect. The device »PIDcon« provides an innovative process for the error analysis of silicon solar cells. With the DIN SPEC 91348, a test standard for the PID tests on silicon solar cells has now been defined for the first time. The German Institute for Standardization e.V. therefore awarded the development as a convincing example of innovative norm and standardization projects. The award was presented by Rüdiger Marquardt, member of the board of DIN.

»I am very happy about this award. The award is evidence of the importance of an accurate knowledge of the microstructure for the reliability of materials. And it also recognizes that with our process we offer an important help for photovoltaic manufacturers and suppliers,« Naumann says.

With »PIDcon«, solar cells or encapsulation materials can be tested for susceptibility to PID in a simple procedure. The production of complete solar modules and their testing in large climatic chambers are being omitted. Instead, the device already allows the PID test for individual, non-encapsulated solar cells. This means significantly lower material, energy and labor costs as well as a process that is easier to handle with less expensive equipment, delivering the test result within a few hours - a decisive advantage for quality control and the production of PID-insensitive solar cells and modules.

Since 2014 »PIDcon« has been offered commercially, the test method is met with great demand. With a DIN standard, the DIN SPEC 91348, the original drawback of the cell test - there was still no standardized test procedure - was eliminated because the PID test procedure is now for the first time also possible on the basis of a test standard for unencapsulated solar cells.