ITO based transparent and conducting thin films for space, solar energy and flexible electronics applications

Abstract

This thesis reports deposition, optimization and investigation of properties of transparent and conducting ITO and ITO/Ag/ITO multilayer thin films for space, solar energy and flexible electronics applications. ITO thin films were deposited on various substrates by pulsed direct current reactive magnetron sputtering system using an In:Sn (90-10 wt.%) alloy target. The influence of the deposition parameters (argon and oxygen flow rates, and substrate temperature) and effect of coating thickness on the optical, electrical, structural and microstructural properties of ITO thin films deposited on flexible fluorinated ethylene propylene (FEP) substrates was investigated in detail. The optimized ITO coating (10-15 nm thick) on FEP substrate exhibited high IR emittance (>75%), high average solar transmittance (>90%) and moderate sheet resistance (2-10 kΩ/square) needed for spacecraft application. Stability of the ITO coatings on FEP, Kapton® and aluminized Kapton® substrates was studied in simulated space environments. Environmental tests such as: relative humidity, thermal cycling and thermo vacuum were performed. Thermo-optical properties and sheet resistance of ITO coated FEP and Kapton® substrates were studied before and after environmental tests. In another objective of the thesis, ITO/Ag/ITO (IAI) multilayer coatings were designed for spectral beam splitter and flexible electronic applications and these coatings were deposited on glass, and flexible FEP and Kapton® substrates by magnetron sputtering method at room temperature. The thicknesses of the component layers, namely, Ag and ITO were varied to achieve high visible transmittance, high NIR-IR reflectance, low sheet resistance, and optimum cut-off wavelength. The optimized IAI multilayers for solar segregator application exhibited high visible transmittance (~91%) and high NIR-IR reflectance (>90%) with an optimum cut-off wavelength of ~900 nm. The optimization of IAI multilayer coatings for transparent conductor also reported in this thesis. High visible transmittance (~ 91%) and low sheet resistance ~7.1 Ω/square were achieved for IAI multilayer deposited on flexible FEP substrate.