Electrical Signatures of Corrosion and Solder Bond Failure in c-Si Solar Cells and Modules

Moisture- and temperature-activated corrosion of metal fingers, mechanical stress induced delamination, and failure of solder bonds rank among the leading failure mechanisms of solar modules. The physics of moisture ingress, diffusion, and reaction have been explored in detail, but the electrical implications of corrosion and delamination on specific front-surface grid geometry is not fully understood. In this paper, we show that the module efficiency loss due to corrosion, delamination and solder bond failure (CDS) involves a complex interplay of voltage/current redistribution, reflected as a loss in photocurrent, as well as decrease/increase in shunt/series resistances. The analysis presented in this paper will redefine the interpretation of experimental I-V characteristic features due to degradation mechanisms, integrate a variety of scattered and counter-intuitive experimental results within a common theoretical framework, and inform CDS-resistant grid design for solar modules.

I. Introduction

The levelized cost of electricity of solar energy can be reduced by lowering the manufacturing cost, increasing the efficiency of the cells, and enhancing the reliability of the modules. Thus, the ability to predict the lifetime and improve the reliability of modules plays a pivotal role in commercial photovoltaic (PV) systems. Among various reliability issues [e.g., yellowing, potential induced degradation (PID), partial shading, etc.], Jordan et al. identified internal circuitry (IC) discoloration caused by corrosion as the second most significant degradation mode in the systems installed in the past ten years [1]. Indeed, corrosion, delamination, solder bond failure (CDS) have always played a critical role in defining module lifetime [2], [3].