Effects of pre-strain applied at a polyethylene terephthalate substrate before the coating of Al-doped ZnO film on film quality and optical and electrical properties

Five kinds of polyethylene-terephthalate (PET)/aluminum-doped zinc oxide (AZO) specimen were prepared to examine the effect of strain applied to the PET substrate before the coating of AZO film on the mechanical, optical, and electrical properties and morphology. An increase in the strain of PET increases the reflection intensity, resulting in a significant reduction in absorption. The largest mean surface roughness was obtained for the PET-4%/AZO specimen. XRD diffraction peaks of ZnO (002) indicate that the quality of the AZO film initially improved with increasing strain, and then degraded with further increases. Compressive residual stresses formed in the bending specimens at various strains; the residual stress increased with decreasing 2θ angle. A higher compressive stress in the AZO film resulted in a lower optical band gap and a lower transmittance; it also led to an increase in the sheet resistance of the AZO film, and thus a lower carrier mobility.