1. The role of oxygen doping on elemental intermixing at the PVD‐CdS/Cu (InGa)Se 2 heterojunction
- Author
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Joel B. Varley, Xiaoqing He, Jeff Bailey, Angus Rockett, Dmitry Poplavskyy, Atiye Bayman, Neil Mackie, Vincenzo Lordi, Geordie Zapalac, Peter Ercius, and Tim Nagle
- Subjects
010302 applied physics ,Materials science ,Renewable Energy, Sustainability and the Environment ,Doping ,Energy conversion efficiency ,Analytical chemistry ,Heterojunction ,02 engineering and technology ,021001 nanoscience & nanotechnology ,Condensed Matter Physics ,Epitaxy ,01 natural sciences ,Copper indium gallium selenide solar cells ,Electronic, Optical and Magnetic Materials ,Sputtering ,Physical vapor deposition ,0103 physical sciences ,Scanning transmission electron microscopy ,Electrical and Electronic Engineering ,0210 nano-technology - Abstract
Author(s): He, X; Ercius, P; Varley, J; Bailey, J; Zapalac, G; Nagle, T; Poplavskyy, D; Mackie, N; Bayman, A; Lordi, V; Rockett, A | Abstract: Elemental intermixing at the CdS/CuIn 1−x Ga x Se 2 (CIGS) heterojunction in thin-film photovoltaic devices plays a crucial role in carrier separation and thus device efficiency. Using scanning transmission electron microcopy in combination with energy dispersive X-ray mapping, we find that by controlling the oxygen in the sputtering gas during physical vapor deposition (PVD) of the CdS, we can tailor the degree of elemental intermixing. More oxygen suppresses Cu migration from the CIGS into the CdS, while facilitating Zn doping in the CdS from the ZnO transparent contact. Very high oxygen levels induce nanocrystallinity in the CdS, while moderate or no oxygen content can promote complete CdS epitaxy on the CIGS grains. Regions of cubic Cu 2 S phase were observed in the Cu-rich CdCuS when no oxygen is included in the CdS deposition process. In the process-of-record sample (moderate O 2 ) that exhibits the highest solar conversion efficiency, we observe a ~26-nm-thick Cu-deficient CIGS surface counter-doped with the highest Cd concentration among all of the samples. Cd movement into the CIGS was found to be less than 10nnm deep for samples with either high or zero O 2 . The results are consistent with the expectation that Cd doping of the CIGS surface and lack of Zn diffusion into the buffer both enhance device performance.
- Published
- 2018