Performance of large area thin film Si:H modules: a link between shunting and stability

A connection is emerging between stability of TFS (thin film Si:H) modules and the degree of shunting; physical shunting is found to increase during light soaking, and it appears that this increase can be a cause of excessive degradation. Outdoor and accelerated light-soaking test results are presented which suggest this link, and a tentative model is presented. In outdoor exposure testing it was observed that modules tend to divide into two groups. Those with relatively good as-built shunt characteristics stabilize with ≈23% power loss. In contrast, those with poorer as-built shunting have less predictable stability, and can show significantly greater power loss, up to more than 30%. The as-built shunting density appears to be an important factor which can influence stability. Implications for large-area module manufacture are considered