Alkali ion migration control from flat glass substrates

Abstract

Sodium diffusion from flat glass substrates during annealing changes properties of refined flat glass. In the ease of the development of the CuInSe2 thin film solar eell, annealing at 550 °C is necessary for the formation of suitable crystalline phases. Sodium diffusing from the soda-lime-silica glass substrate influences crystal growth and the main electrical parameters of the solar cell. Different possibilities in sodium ion migration control are presented, considering the influence of glass composition on sodium diffusion and its chemical potential as well as passivation of sodium-containing glasses by diffusion barriers. Experimental results in connection with the thin film solar cell show that sodium-free substrates or glass compositions which immobilise sodium at tetrahedral sites of boron oxide or alumina can be used without further surface treatment. Soda-lime-silica glass with sputter-deposited AI2O3 and BiOx thin films or CVD coatings (SiNx: H, SiOx) as diffusion barrier coatings shows promise as a cheap substrate material. Alternatively, dealkalisation of soda-lime-silica glass in HCl atmosphere leads to silica-rich surfaces with excellent barrier properties. The investigations are carried out using various surface analytical tools like Auger Electron Spectroscopy (AES), X-Ray Diffractommetry under Grazing Incidence (GI-XRD), high-resolution Scanning Electron Microscopy (SEM), and Fourier Transform Infrared spectroscopy (FTIR).