Durable TiN/TiNx metallic contacts for solar cells

A new structure of durable metallic thin film contacts for solar cells has been investigated. Stoichiometric titanium nitride (TiN) with a thin non-stoichiometric titanium nitride (TiNx) buffer layer was used to give the desirable mechanical properties and metallic behavior. The metallic contacts were deposited by dc reactive magnetron sputtering using negative rf bias voltage on glass substrates. The target was Ti (99.95% purity) and the reactive gas was N2 (99.999% purity). In situ and ex situ spectroscopic ellipsometry (SE) was employed to study the metallic behavior of the deposited thin films in terms of unscreened plasma energy ωpu of the material. The study showed that TiN/TiNx films exhibited the same, good metallic behavior with TiN films. The cohesion and the adhesion of the TiN and TiNx to the glass substrate were investigated by employing scratch test and lateral force measurements. It was found that all the investigated metallic contacts remain cohered during the scratch test, but only the proposed TiN/TiNx metallic contact stayed adhered to the substrate. Thus, improved service life together with high performance is expected for the solar cells based on the proposed metallic contacts.