High temperature induced mechanical degradation in flexible solar cell and its effect on reliability of the packaging module

Polymer based organic photovoltaic systems, which can be mass-produced by roll-to-roll printing technology, hold the promise for a cost-effective, lightweight and mechanical flexible solar energy conversion platform. Nevertheless, challenges still remain for large-scale applications of these flexible solar cells. One of the issues of great importance is the long-time reliability of solar cell module. It is demonstrated that organic solar cells can have wide range of applications, and therefore the surrounding temperature, humidity and load conditions vary. Rapidly changing thermo-mechanical loads often produce early failure of certain parts of the solar cell module, or even fracture of overall packaging which may result in the degradation of performance and life of solar cell. Therefore our work mainly focuses on the effect of elevated temperature on mechanical properties of materials in flexible solar cell panel. Temperature induced mechanical degradation and its effect on reliability of the packaging module are investigated. In our test, the samples made from flexible solar cell panel are stretched at a certain strain rate by test machine at 25°C, 75°C and 125°C, respectively. We find that Young's modulus of the materials decrease sharply with increasing temperature from the nominal stress-strain curve of materials and interfacial delamination occurs prior to material fracture at higher temperatures. Test results indicate that high temperature will not only reduce the mechanical stiffness of the materials in flexible solar cell, but also weaken the tensile strength of the material, which eventually undermined the reliability of solar cell packaging.