The direct correlation of CDTE solar cell stability with mobile ion charge generation during accelerated lifetime testing

CdS/CdTe cells deposited on cadmium and zinc stannate (CTO/ZTO) transparent conducting oxide (TCO) substrates show greater degradation than similar devices fabricated on SnO₂-based substrates. This has been confirmed in two separate studies in which J-V changes during stress suggest different degradation mechanisms believed to be due to differences in processing. In addition, cells made using the CTO/ZTO substrates exhibit greater variations in initial performance relative to SnO₂-based substrates. A capacitance-voltage (CV) method using different initial bias conditions is used to quantify mobile ion concentration. CV hysteresis was observed in Cu-containing cells and was absent in cells that were not intentionally doped with Cu. With increasing stress, hysteresis increased. A faster rate of hysteresis gain was observed in CTO/ZTO cells relative to SnO₂ cells. A model is introduced for explaining the origin of the hysteresis and why it increases with increasing stress.