Effects of prestrain applied to poly(ethylene terephthalate) substrate before coating of indium–tin–oxide film on film quality and optical, electrical, and mechanical properties

Four kinds of poly(ethylene terephalate) (PET)/indium–tin–oxide (ITO) specimen were prepared to examine the effect of prestrain applied to the PET substrate before the coating of ITO film on the mechanical, microstructure, optical, and electrical properties and morphology. The dependence and interaction among these properties/parameters are established and discussed. The mean slenderness ratio of the crystalline porosities in the ITO film decreased with increasing prestrain. The tilt angle of tubular porosities increased due to the increase in the particle size of ITO deposited on the PET substrate. A nonzero prestrain reduced both interplanar spacing (d-spacing) and the mean surface roughness of the ITO film. An increase in the substrate prestrain decreased the mean transmittance but increased the mean reflectance of the specimens. An increase in the ITO particle size lowered the optical band gap (Eg) and mean reflection and increased the mean transmittance. PET/ITO specimens with larger Eg values had higher carrier mobility (Mb). A nonzero prestrain leads to a smooth ITO film with low electrical resistance. Decreasing Young's modulus in combination with increasing specimen's hardness is helpful to the increase in the pop-in depth and the decrease in the pop-out depth in the nanoindentations. The electrical current–depth curve from nanoindentation tests and the stress–depth curve can be used to efficiently identify the depths of pop-in and pop-out. The PET/ITO specimen with 2% prestrain had the largest pop-in depth and the smallest pop-out depth.