Silicon Heterojunction System Field Performance

A silicon heterostructure photovoltaic system fielded for 10 years has been investigated in detail. The system has shown degradation, but at a rate similar to an average Si system, and still within the module warranty level. The power decline is dominated by a nonlinear V_oc loss rather than more typical changes in I_sc or Fill Factor. Modules have been evaluated using multiple techniques including: dark and light I-V measurement, Suns-V_oc , thermal imaging, and quantitative electroluminescence. All techniques indicate that recombination and series resistance in the cells have increased along with a decrease of factor 2 in minority carrier lifetime. Performance changes are fairly uniform across the module, indicating changes occur primarily within the cells.