Impurity and self-diffusion related to the copper sublattice in CIGSe thin-film solar cells

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The proposal aims at the comprehensive characterization of diffusion processes in Cu(In,Ga)Se2 (CIGSe) layers, in order to provide a scientific basis for the further optimization of the corresponding thin-film solar cells. The scheduled investigations concern both Cu self-diffusion and the diffusion and solubility of the impurity elements Ag and Na, which are likely to be accommodated by the Cu sublattice and are of great importance for CIGSe technology. In particular, it is planned to elucidate - by elaborate experiments in poly- and monocrystalline CI(G)Se layers - the anomalous diffusion behaviour of Ag and Na that was observed during the first period of the project. Comparing the properties of impurity diffusion with those of self-diffusion should make it feasible to detect the lattice defects involved, such as, e.g., vacancies and grain boundaries, and to identify the diffusion mechanism in each case. The main experimental method is radiotracer diffusion profiling, which will be supplemented by mass-spectroscopic measurements using SIMS analysis. Additional data on solubility and segregation will be obtained by examinations on a near-atomic scale using atom-probe analysis.