Influence of current density on Al:NiO thin films via electrochemical deposition: Semiconducting and electrochromic properties

Abstract

The uniform aluminum-doped nickel oxide (Al:NiO) thin films were fabricated on indium tin oxide (ITO) by an efficient route of galvanostatic mode together with the help of conventional electrochemical methods. The cathodic deposition current densities were increased from 4 mA cm−2 to 7 mA cm−2 by a step of 1 mA cm−2 for the growth time of 30 s. The produced films were annealed in air at 400 °C for 1 h. The effect of deposition current on the behaviors of Al:NiO thin films were investigated by a number of methods including scanning electron microscopy (SEM), energy dispersive X-rays analysis (EDX), X-ray diffraction (XRD), Ultraviolet–Visible (UV–Vis) spectroscopy, Mott-Schottky analysis, and electrochemical impedance spectroscopy (EIS). X-ray diffraction analysis confirms the crystallinity of all deposits. SEM studies indicate that the surface morphologies of Al:NiO alter sensitively depending on the applied current density. From chronoamperometric curves of the two stage of the produced films, the fastest response times are found to be tb = 0.85 s and tc = 1.90 s for Al:NiO at an applied current density of 4 mA cm−2. It is found that the average coloration efficiency (η) reaches to a value of 50 cm2/C for Al:NiO fabricated at 5 mA cm−2. Significantly, the electrode displays long-term cyclic durability after 500 cycles in the potential window from 0 to +0.8 V in 0.1 M potassium hydroxide (KOH) aqueous solution. The concept of Mott-Schottky is considered as approach that confirms the p-type semiconducting behavior of all the Al:NiO films with the order of ~1012 - 1015 cm−3 acceptor density. The results demonstrate promising electrochemical properties to enhance the electrochromic performance of NiO thin films which is required for the growth of outstanding electrode materials in smart glass and open a new insight into further applications of devices.