Multi-scale simulation of Mo–Ag laminated metal matrix composites with Mo–Ag diffusion layer and parallel gap resistance welding in solar cells

Abstract

Thus far, Mo/Ag laminated metal matrix composites (LMMCs) have been widely used as interconnectors in solar cells. In order to enhance the connection strength between Mo–Ag LMMCs and solar cells, a multi-scale simulation technique (MSM) was utilised to simulate the parallel gap resistance welding (PGRW) process. This method involved molecular dynamics (MD) simulation and the finite element method (FEM). The structure of the Mo–Ag diffusion layer was examined by high-resolution transmission electron microscopy (HRTEM), which revealed a thickness of around 5 nm. It exhibited a wedge-shaped configuration that augmented the bonding between Mo and Ag. The characteristics of the Mo–Ag diffusion layer were computed using molecular dynamics (MD), which has a substantial influence on the properties of the interconnectors. The FEM model was provided with these characteristics, and a total of nine sets of orthogonal simulation experiments were devised. The findings indicate that when a voltage of 0.5 V is applied, the distance between the electrodes is 0.15 mm, and the pressure on the electrodes is 8.89 N, the temperature at the interface of the workpiece can reach 940 °C. Furthermore, the internal stress (90 MPa) remains below the material's yield strength (430 MPa). In addition, based on the specifications of nine sets of orthogonal trials, the interconnectors were welded to the solar cells, and further 45° tensile tests were performed on the resulting joints. According to the simulation, the connection strength can achieve a maximum value of 558 gf (5.47 N) using the optimal parameters. Meanwhile, the findings from electron backscatter diffraction (EBSD) revealed that the primary process involved in the connection mechanism of PGRW is the mutual diffusion and recrystallization that occur due to electrode pressure and resistance heat.

Keywords

• Parallel-gap resistance welding (PGRW)
• Multiscale simulation method
• Mo–Ag diffusion layer
• Molecular dynamics (MD)
• Finite element method (FEM)
• Orthogonal experimental design