Spatially-resolved intensity monitoring in illuminated belt furnaces with a heat-resistant data tracker

This mobile intensity tracker for solar module production withstands the high temperatures in a continuous furnace belt for a short time and can therefore be transported through the furnace together with solar cells. For the first time, reliable intensity measurements can be carried out directly during the regeneration process of cells and the processes can be efficiently monitored and optimized during operation. In the future, the system will contribute to a constantly higher efficiency of solar cells.

The regeneration of recombination-active defects in monocrystalline silicon solar cells is a standard step in their production in order to effectively neutralize light-induced degradation (LID) that would otherwise occur during initial illumination. The regeneration treatment comprises intensive illumination at elevated temperatures. If this process does not take place or does not take place in an optimal way, these recombination-active defects remain in the solar cell and reduce its efficiency. An optimally regenerated solar cell can achieve up to 5%_rel higher, long-term stable efficiency. However, the regeneration process developed at the University of Konstanz, which is used worldwide, usually has to be optimized for the specific manufacturing process of the solar cell.

Up to now, there is no measuring system available that is able to reliably measure the light intensity in belt furnaces in a spatially resolved manner without disturbing the running operation, i.e. especially at typical process temperatures in the range of 200-300°C. Up to now, meter-long measuring lances have been used, if at all, whose use requires an interruption of production, or even the belt furnaces to be opened. Alternatively, the power of the light sources is also used to estimate the intensity. A precise control of an industrial regeneration process is thus not possible.

At the University of Konstanz, a mobile intensity tracker has been developed that can withstand the high temperatures in an illuminated belt furnace for a short time and can therefore be sent through the belt furnace together with solar cells. The measuring system consists of an intensity sensor (small solar cell) on a heat sink, which prevents excessive heating due to its thermal mass. The signal of the intensity sensor is recorded by means of electronics protected against high temperatures. The measuring system can be adapted to the specifics of a production line. A fully functional prototype is already available.

• Spatially-resolved intensity measurement in belt furnaces during running operation
• Short-term use even above 200°C
• Optimized regeneration and thus higher solar cell efficiency thanks to an ideal illumination profile
• Mobile measurement system – Retrofitting simple and cost-efficient

Solar cell production: The mobile measuring system presented here enables the light intensity and temperature to be monitored during the regeneration process in an illuminated belt furnace during running operation. It thus allows an optimization of the process parameters and a recurring monitoring without interruption of operation or downtimes.