An innovative packaging process for low power loss solar modules

Abstract

This paper presents an innovative interconnecting process for the 5 inch × 5 inch photovoltaic (PV) modules based on single crystalline silicon solar cells using epoxy-based conductive adhesive (CA), and a conventional soldering type solar cell is also performed for comparison. The electrical performance of solar modules with innovative interconnecting process (Inno 1, 2, and 3) was characterized by a flasher system in AAA class, and the long-term durability of the solar modules was verified by thermal cycling test in accordance with IEC 61215 standard. The result shows that the power loss for innovative stringing solar cell with epoxy-based CA exhibits a two-stage degradation mechanism, in which a higher lossrate occurs before TC 600 times. For Sn-Pb solder solar module, a linear degradation is observed during the 1600 thermal cycling test, suggesting a single degradation mechanism. Compare the power loss of the solar modules, the innovative modules are around 4.31% to 5.21%, while a high power loss of 7.49% is obtained in soldering type module after 1600 TC test. According to the cross-sectional images focusing on the solder joints, a better performance of the epoxy-based CA solar module was due to the good adherence and stability of the soldering interfaces between the cell metallization and the interconnecting element. Electroluminescence (EL) detection was applied to identify the defects and high series resistance area which may degrade the power of the cell. Some dark failure area on the central region after 1600 thermal cycling test (TCT) is shown in soldering type sample. And a high contrast of the emission intensity is obtained, which implies a mismatch of minor carrier diffusion length in the solar cell. The dark regions observed in the soldering type sample indicated that a higher Rs was generated in the module. On the other hand, CA sample showed a clear image on the cell itself and the p-n junction borderline area.