Low Stress Encapsulants? Influence of Encapsulation Materials on Stress and Fracture of Thin Silicon Solar Cells as Revealed by Synchrotron X-ray Submicron Diffraction

Abstract

We study the effect of two polymer encapsulations with different material properties such as Young's modulus (E), yield strength etc. on the residual stress of mono-crystalline silicon. We observe through synchrotron X-ray microdiffraction that, solar photovoltaic (PV) module laminated with encapsulants A (soft) and B (stiff) which have Young's modulus of 6.34 and 28.32 MPa respectively, reveals distinct variations in residual stress of silicon. The stress of silicon measured near the solder (stress concentration region), showed a maximum quantitative value of ∼ 300 MPa with encapsulant A whereas for the solar PV with encapsulant B, it showed a much higher value of ∼ 450 MPa. Further correlation of stress to fracture/crack initiation events of silicon were also understood using three point bending tests. The result shows that with encapsulant A, crack initiation of silicon at a mean force of ∼ 1.2 KN is observed whereas for the PV with encapsulant B, silicon cracked at much lower force of ∼ 0.3 KN. These studies confirm that encapsulant materials have a significant effect on the residual stress of silicon, which directly affects the working efficiency and reliability of the solar PV.