An investigation of the effect and nature of shunts in a-Si solar cells

Shunted cell and module segments cause a reduction in initial efficiency and yield, and can also lead to increased degradation. Shunts in small area (0.25 cm²) cells are apparently the result of a number of small defects which are grouped together in fields and are hypothesized to be linked to imperfections in the tin oxide. The defects which are active in small area diodes also affect large area modules. Modules suffer as well from larger shunt-causing defects which occur preferentially near the module perimeter. The effect of shunting on module initial efficiency can be nearly eliminated by moving the laser isolation scribe 1/2" to 1" away from the edge of the module. The best modules lose only about 15% of their initial efficiency as a result of prolonged light-soaking; however, they more typically lose about 18-25%. Much of this excess degradation can be attributed to shunt formation