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HL: Halbleiterphysik

HL 32: Photovoltaik

HL 32.1: Vortrag

Donnerstag, 14. März 2002, 10:30–10:45, H14

Analysis of interface formation in CdTe/CdS thin film solar cells — •Mathias Terheggen¹, Helge Heinrich¹, Gernot Kostorz¹, Alessandro Romeo², and Ayodhya Tiwari² — ¹ETH Zurich, Institute of Applied Physics, CH-8093 Zurich, Switzerland — ²ETH Zurich, Laboratory for Solid State Physics, Thin Film Physics Group, Technopark ETH-Building, Technoparkstr. 1, CH-8005 Zurich, Switzerland

The p-n interface in CdTe/CdS thin film solar cells is located between the CdTe and the CdS layer. As CdTe and CdS show lattice mismatch, a high defect density and a poor electrical performance of the p-n junction are to be expected. This can be overcome by depositing a CdCl₂ layer on the cell and annealing the stack. The treatment is expected to lead to an interdiffusion of S and Te and to a better lattice match. However, little agreement on the extent of diffusion and the diffusion mechanisms has been achieved. Cells were grown by high vacuum deposition and close space sublimation. Cross sectional samples were studied by transmission electron microscopy. After the CdCl₂ treatment, recrystallization was observed for both the CdTe and CdS layers. The distribution of S, Te and Cl at the interface and at grain boundaries were investigated. The chemical composition at the interfaces was studied directly with energy dispersive X-ray spectroscopy mapping. The diffusion of S is found to depend on the extent of CdCl₂ treatment. While a diffusion of Te at the interface was not observed, segregation of Cl and Te at the CdTe/CdS interface was clearly revealed.