When solar modules are partially shaded they will be under conditions of partial reverse bias. To test and evaluate the effect of reverse bias, CIGS thin film PV modules were placed under extreme conditions of reverse stress. Stressing caused modules to exhibit visible "wormlike" damages. These damages were caused by hot spot activity during reverse stress. Local heating resulted in pore formation and forced the hot spot to move within the cell. This effect appeared to cause intermixing of the top ZnO layer with the CIGS absorber. Some phase segregation of an undetermined, Cu rich compound was also found near the back contact. Electrically, the observed damages caused local shunt conductance to increase resulting in irreversibly reduced module fill factors.
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