CdTe cell stability vs. CdS thickness

We have studied the stability in air of sputtered CdTe/CdS cells with a focus on the thickness of the CdS layer and the substrate used during cell fabrication. The stability of cell efficiencies under light soak is compared for CdTe cells on both HRT-coated Pilkington TEC 15 glass and standard TEC15 glass for a range of seven different CdS layer thicknesses from 0 to 230 nm. Little difference in stability can be found between cells with or without the HRT layer for all CdS thicknesses. The buffer layer helps to produce high initial performance and uniformity of cells by maintaining high VOC for very thin CdS layers. But there is no indication that the buffer layer improves the stability of unencapsulated, sputtered cells under one-sun light soak at open circuit. Devices with the thicker CdS layers show better stability under one-sun light soak in air.