Conducting fluorine doped tin dioxide (FTO) coatings by ultrasonic spray pyrolysis for heating applications

Abstract Fluorine doped tin dioxide (FTO) coatings were deposited on AISI 304 stainless steel (SS) substrates using ultrasonic spray pyrolysis (USP) technique. Four different candidate insulating intermediate layers of TiO2, MgO, Al2O3 and SiO2 were selected and coated on AISI 304 SS using USP and investigated in order to overcome dielectric breakdown of FTO layer due to conductive nature of stainless steel substrate under the applied voltage. After the optimization of the process parameters for the depositions, only TiO2 layer was successfully deposited while other oxides did not form continuous films on AISI-304 SS surface despite the efforts. SEM analysis, supported by back-scatter imaging, revealed thickness values of the layers for FTO and TiO2, individually. Heating performances of the samples with varying sheet resistance values were examined under different applied voltages. Heating experiments showed that 300 °C can be reached with 10 V of applied voltage without occurrence of an electrical breakdown of FTO coating having 160 nm thickness with TiO2 intermediate layer of 660 nm. 28.6% efficiency for the conversion of electrical energy into heat was calculated for FTO coating while bare stainless steel showed only 7.3% efficiency. Later, the heating experiments were repetitively conducted and the samples were tested under high relative humid environment to determine their resistance against moist conditions.