One route to achieve thick YBCO layers by a single deposition on single crystal substrates (LAO) has been to modify the viscosity of the solution by using different polymeric agents in precursor solutions. A screening investigation of several polymers with different molecular weights has been performed to choose the best additive based on the following criteria : to increase viscosity, to avoid any chemical reaction with the precursors and to keep the same decomposition temperature as compared to the pyrolysis of the TFA precursors. Solution viscosity, thermal and thermo-gravimetric analysis measurements have been used to characterize the TFA solutions with the additives. An increase of the YBCO films thickness of 100% (600nm) has been demonstrated keeping a high Jc 1.1 MA/cm2 (77K). © 2006 IOP Publishing Ltd.