Overcoming degradation mechanisms in CdTe solar cells: First annual report, August 1998--August 1999

The authors have studied the importance of chemical processes for the stability of CdTe solar cells, in particular, diffusion in the ohmic contact/absorber junction regions. Both whole cells and test systems containing only the ohmic contact and the absorber are used. They found several experimental methods to be useable tools to follow the effects of impurity diffusion on the CdTe grain boundaries, grain bulk, and surface. In addition, they have explored alternative contacting schemes. The first year of activities led to the following tentative conclusions: Grain boundaries in CdTe/CdS cells are NOT fully passivated and are expected to be electrically active; There appears to be fast ionic diffusion in the vicinity of the Cu/HgTe/graphite back-contact, possibly enhanced by grain boundary diffusion; The macroscopic response to stress is different for cells with identical back-contact, but from different manufacturers. Different factors and/or different reactions to identical factors are possibly at work here; and Ni-P appears to be a promising back-contact material