CdCl2 Activation of Wide Bandgap II-VI Alloys with Capping Layers
Carey L Reich1,2,3, Arthur Onno2, Drew E Swanson2,3, Tushar Shimpi1, Anna Kindvall1, Andrew Ferguson3, Wyatt K Metzger3, Walajabad S Sampath1, Zachary C Holman2
1Colorado State University, Fort Collins, CO, United States
/2Arizona State University, Tempe, AZ, United States
/3National Renewable Energy Laboratory, Golden, CO, United States

Alloys of the II-VI semiconductor CdTe with Mg or Zn have tunable bandgaps in the range modelled to be optimal for integration as a top cell in a tandem photovoltaic device with a Si bottom cell. Leveraging the low-cost production techniques developed for CdTe, this pairing has the potential to produce low-cost and highly efficient tandem PV cells. However, the CdCl2 post-deposition bulk passivation process widely used for CdTe reduces the concentration of the ternary elements in the absorber, reducing the bandgap from the modelled values, and shows poorer activation than the same process applied to the base CdTe material. We study the effectiveness of the CdCl2 passivation on CdMgTe and CdZnTe when CdTe, CdS, MgZnO, or Al2O3 cap the back absorber surface to provide a barrier to Mg or Zn out-diffusion. For example, using CdS as a barrier layer during CdCl2 produces relatively high efficiency CdMgTe (7.4%) and CdSeTe/CdMgTe (10.6%) devices.

Area: Sub-Area 2.1: Absorber Preparation and Material Properties