SiOxNy back-contact barriers for CZTSe thin-film solar cells

The formation of molybdenum diselenide (MoSe2) is widely observed at the back-contact interface for copper zinc tin selenide (CZTSe) thin-film solar cells. Depending on individual selenium (Se) supply and thermal conditions for forming CZTSe absorbers on molybdenum (Mo) substrates, the thickness of MoSe2 can vary from a few hundreds of nanometers up to ≈ 1 μm, which is comparable to the commonly adopted thickness of 1 ~ 1.5 μm for CZTSe absorbers. In this study, for controlling the thickness of interfacial MoSe2, thin diffusion barrier layers of silicon oxynitride (SiOxNy) are deposited onto Mo layers prior to the growth of CZTSe absorbers in the fabrication process. As a result, a reduction in the thicknesses of MoSe2 layers is achieved. In terms of energy conversion efficiency (η), CZTSe solar cells grown on Mo/SiOxNy back contacts suffer a deterioration as the SiOxNy layers get thicker. CZTSe solar cells grown on Mo/SiOxNy/Mo back contacts preserve their efficiencies at ≈ 11% with thin 10 nm SiOxNy layers.

Modifications of the CZTSe/Mo back-contact interface by plasma treatments

Molybdenum (Mo) is the most commonly used back-contact material for copper zinc tin selenide (CZTSe)-based thin-film solar cells. For most fabrication methods, an interfacial molybdenum diselenide (MoSe₂) layer with an uncontrolled thickness is formed, ranging from a few tens of nm up to ≈1 μm. In order to improve the control of the back-contact interface in CZTSe solar cells, the formation of a MoSe₂ layer with a homogeneous and defined thickness is necessary. In this study, we use plasma treatments on the as-grown Mo surface prior to the CZTSe absorber formation, which consists of the deposition of stacked metallic layers and the annealing in selenium (Se) atmosphere. The plasma treatments include the application of a pure argon (Ar) plasma and a mixed argon–nitrogen (Ar–N₂) plasma. We observe a clear impact of the Ar plasma treatment on the MoSe₂ thickness and interfacial morphology. With the Ar–N₂ plasma treatment, a nitrided Mo surface can be obtained. Furthermore, we combine the Ar plasma treatment with the application of titanium nitride (TiN) as back-contact barrier and discuss the obtained results in terms of MoSe₂ formation and solar cell performance, thus showing possible directions of back-contact engineering for CZTSe solar cells.

Molybdenum (Mo) is the most commonly used back-contact material for copper zinc tin selenide (CZTSe)-based thin-film solar cells. The effect of a pure Ar plasma and a mixed Ar–N₂ plasma on the back-contact interface of CZTSe solar cells is reported in this study.

Testing the Uniform Needs Assessment Instrument for hospital discharge planning with older adults

The Uniform Needs Assessment Instrument (UNAI) was developed to systematically assess the continuing care needs of high-risk older adults in response to the 1986 Omnibus Budget Reconciliation Act. Based on previous studies, a revised UNAI was tested with 103 hospitalized older adults, comparing usual discharge planning with the UNAI. High interrater reliability was obtained. The UNAI had high (> or = 85%) sensitivity and specificity when comparing needs identification on the UNAI with subjects' reported needs at 10 to 14 days after discharge. Overall, the UNAI was more effective (sensitive and specific).