Multilayer SnO2:Sb transparent electronic conducting coatings made by the sol-gel process

Abstract

Transparent conducting thin sol-gel SnO2:Sb multilayer coatings having the same total thickness, but different numbers of layers have been deposited on borosilicate glass by the dip-coating method using an ethanolic solution of SnCl2 (OAc)2 doped with 5mol% SbCl3. The densification of the multilayers was done by 3 different processes. In process I each layer was dried at 200°C and the coating process repeated to obtain a tick dry coating which was then sintered as a whole at 550°C. In process II every single layer was dried at 120°C and then directly sintered at 550°C before repeating the coating process. In process III every single layer was directly sintered at 550°C without drying step. The electrical properties and the morphologies of the coatings depend highly on the sintering and drying conditions. With process I all layers are homogenous and have a high resistivity (1.4x10 -² Omega cm) whatever their thickness. The multilayers produced by process II and III show a sandwich structure with alternated dense and porous layers. The resistivity of a 10 times dipped multilayers obtained by these processes is about 3,2X^0 -³ Omega cm. Moreover the electrical properties vary with the number of layers whereas in process I no such correlation can be found. A model was developed which allows to caclulate the electrical properties of the dense and porous layers. The chemical composition of the homogeneous coating and of the multilayers with the alternated structure is also reported.