Alkali ion migration control from flat glass substrates

Sodium diffusion from flat glass substrates during annealing changes proper ties of refined flat glass. In the case of the development of the CuInSe2 t hin film solar cell, annealing at 550 degrees C is necessary for the format ion of suitable crystalline phases. Sodium diffusing from the soda-lime-sil ica glass substrate influences crystal growth and the main electrical param eters of the solar cell. Different possibilities in sodium ion migration co ntrol are presented, considering the influence of glass composition on sodi um diffusion and its chemical potential as well as passivation of sodium-co ntaining glasses by diffusion barriers. Experimental results in connection with the thin film solar cell show that sodium-free substrates or glass com positions which immobilise sodium at tetrahedral sites of boron oxide or al umina can be used without further surface treatment. Soda-lime-silica glass with sputter-deposited Al2O3 and BiOx thin films or CVD coatings (SiNx:H, SiOx) as diffusion barrier coatings shows promise as a cheap substrate mate rial. Alternatively, dealkalisation of soda-lime-silica glass in HCl atmosp here leads to silica-rich surfaces with excellent barrier properties. The i nvestigations are carried out using various surface analytical tools like A uger Electron Spectroscopy (AES), X-Ray Diffractommetry under Grazing Incid ence (GI-XRD), high-resolution Scanning Electron Microscopy (SEM), and Four ier Transform Infrared spectroscopy (FTIR).