Conductive adhesive based shingled solar cells: Electrical degradation under cyclic loading

Abstract

Shingled solar cells based on electrically conductive adhesive (ECA) interconnection have emerged as a commercially viable option for photovoltaic (PV) modules with attractive attributes including no soldering process (lead-free), tight packing with no gap between cells, and resulting efficiency gains. Reliability of such modules is, however, less certain due to the lack of long-term outdoor performance data. Here we report numerical simulation of thermo-mechanical stress in shingled solar cells using finite element modelling, and identify stress concentration in silicon in the interconnect region not anticipated from simpler analytical models. We also present design and fabrication of samples using ECA interconnection with geometry and characteristics that closely match production modules for realistic fatigue testing under cyclic loading. The setup is combined with real-time electrical measurements that permit monitoring of fatigue-induced changes in the electrical resistance of ECA joint. Detailed measurements are presented using samples with different types ECA and varying patterns of the glue-line aimed at evaluating reduced material usage for cost-reduction. This study demonstrates that the sample structure and experimental setup presented here can be effectively used to evaluate electrical and mechanical degradation of shingled PV modules to guide their design process.