In the photovoltaics industry, the need to reduce peripheral cracks on solar cells has received much attention. Thin film modules of CDTE or CIGS on glass or flexible substrates are susceptible to moisture ingress and require stringent quality control checks. Pressurex®, a pressure indicating film, is useful in checking quality. The film reveals pressure magnitude and distribution between any contacting or mating surfaces, which is useful for quality control checks during equipment setup, calibration, as well as re-qualification of a solar module production line. Negative occurrences such as cracked substrates squeeze out of materials from the module, and unwanted encapsulant thickness can be reduced, if not eliminated, by measuring and controlling applied pressure.
When placed at the interface of two contacting surfaces compressed together (as in a lamination or heat press, for example), the film measures pressure from 2 – 43,000 PSI (0.14 – 3,000 kg/cm²). It assures proper pressure magnitude to cause polymerization and securely bond multiple layers together during EVA and PVB lamination. To ensure even pressure distribution over the entire module during the press cycle, the film is placed into the assembled module layup stack. Then, force from the press is applied. The film captures this applied force permanently and irreversibly through a change in color. The intensity of the color change is proportional to the amount of pressure applied. Precise determination of pressure magnitude and distribution can be obtained by comparing the resultant sensor film’s color to a color calibration reference chart. A “pressure map” control sample can then be created and used for process control.
During the frame press stage, Pressurex® helps verify adequate frame-to-module placement and edge sealing. During the solar cell metallization stage, it checks pressure uniformity of the heat press that applies wire grid and bus bar components to the top conductive layer of the solar cell. Due to the relatively high temperature of the heat-press in the metallization process (>200° C), the film is covered by a layer of TemprX® film to shield it from the heat. The film stack is placed on top of solar cell and when the press is engaged it forms a pressure imprint. Alternatively, the pressure imprint can be taken with the heat turned off and without TemprX®.
Sensor Products Inc
Filed Under: Energy management + harvesting, Green engineering, Sensors (position + other)