Comparative study of transparent conductive In2O3:Sn (ITO) coatings made using a sol and a nanoparticle suspension

Transparent conducting In2O3:Sn (ITO) layers have been deposited by spin coating on glass substrates using two different solutions, an ethylene glycol solution of indium and tin salts (sol) and a suspension of crystalline ITO nanoparticles redispersed in ethanol. The coatings have been sintered in air at 550 degrees C for 30 min. and then post annealed in a reducing atmosphere at 300 degrees C for 30 min. The electrical, optical, morphological and mechanical properties of both types of coatings are compared. The use of the suspension leads to thick 500 nm single layers with a specific resistivity rho = 1.6 x 10(-2) Omega cm but only very thin ones, about 12 nm for a single layer, with rho = 1.8 x 10(-3) Omega cm (a factor of 10 smaller) are obtained using the sol. The resistivity still decreases down to a minimum rho = 6 x 10(-4) Omega cm for multilayer coatings, a value quite close to that obtained by PVD or CVD processes. These differences originate from the different morphologies of the coatings. The conventional sol-gel layers exhibit a columnar structure with a low porosity (28%) while the others have a granular structure with a high porosity (51%). Correspondingly the electron mobility mu is 14 and 1.1 cm(2)/V s, respectively. The visible transmission of both types of layers is high (T>85%). The influence of the sintering temperature is also discussed. (c) 2005 Elsevier B.V. All rights reserved.