Degradation kinetics of CIGS solar cells

The moisture-induced degradation rate of CIGS solar cells at 22–85oC and 0#x2013;100% RH has been measured and fit to a kinetic rate expression. This expression is coupled to a model of moisture diffusion into a package and typical meteorological input data to create a cumulative damage model to predict lifetime of packaged cells. Analytic solutions are also derived. In the diffusion-controlled regime, the life depends on the square root of package permeability and cell degradation rate. Early results indicate that a barrier of ≪10 −4 g/m 2 /day or better will be required to assure 20 year lifetime in Miami for the Global Solar cells used here. Other less stable cells will require 10–100X better moisture barrier. Estimated acceleration factors for damp heat (85C/85%RH) vs. Miami range from 15X to 50X, depending on the package, since diffusion through the package is accelerated differently than the cell degradation kinetics. These low accelerations are a direct result of the square root dependence in this diffusion-controlled process.