Sputter deposited transition metal nitrides as back electrode for CIGS solar cells

Transition metal nitrides such as TiN and ZrN have a potential use as back electrodes in Cu(In,Ga)S2 or Cu(In,Ga)Se2 solar cells. Important properties of the back electrode are its conductivity, reflection at higher wavelengths, mechanical and chemical stability, and its barrier properties for impurity diffusion when metal foils are used as flexible substrate for the solar cells. Here, TiN thin films were deposited with reactive magnetron sputtering and were characterized with Rutherford backscattering spectroscopy, X-ray reflection, ellipsometry and UV-Vis-NIR optical spectroscopy. The resulting thin film density and optical reflection were characterized and compared to the particle fluxes towards the substrate. Therefore, the total momentum flux, total energy flux and momentum flux of target species towards the growing film were measured or simulated. A distinct relation between the density and optical reflection of the TiN films and the momentum flux of target species towards the substrate is shown.