The Effect of Concentration of Aluminum on Structural, Optical, and Electrical Properties of Aluminum-doped ZnO Nanostructures Electrochemically Deposited on Polyimide

Aluminum-doped ZnO (AZO) were successfully prepared on polyimide (PI) film using electrochemical deposition. Field emission scanning electron microscopy (FESEM) analysis revealed that as the aluminum concentration increased, the morphology of AZO nanostructures changed from pellets to nanorods. X-ray photoelectron spectrometry (XPS) was employed to study the chemical states of undoped and Al-doped ZnO on a polyimide substrate. The X-ray diffraction (XRD) patterns of the PI/AZO nanostructures showed a polycrystalline wurtzite structure with a crystallographic orientation along the (002) plane. The XRD analysis also indicated that the average crystallite size decreased from 50.5 nm to 31.0 nm with increasing aluminum concentration (from 0.05 mM to 10 mM). Transmittance analysis revealed that with increasing aluminum concentration, the average optical transmittance in the visible region decreased from 90 % to 75 %. The aluminum concentration has a significant effect on the electrical properties of the samples, as shown by current-voltage (I-V) and Hall measurements. Among the samples, the AZO/PI film prepared with 5 mM aluminum concentration exhibited the minimum electrical resistivity (4.14x10(-2 )Omega.cm), the highest carrier density (1.10x10(21) cm(-3)) and the Hall mobility (5.40 cm(2) V(-1 )s(-1)). We also discuss the possible mechanisms underlying these results compared to undoped ZnO films. This study contributes to the potential applications in flexible electronics and optoelectronics by demonstrating the tunability of AZO nanostructures on a flexible polyimide substrate through controlled aluminum doping.