Temperature dependence of the electrochromic properties of complementary NiO//WO3 based devices

Abstract The influence of the cycling temperature, up to 80 °C and down to −10 °C, on the performances of the electrochromic device ITO/NiO/electrolyte/WO3/ITO (NiO//WO3) and symmetrical devices ITO/LixWO3 (colored)/electrolyte/WO3 (bleached)/ITO (WO3//WO3), ITO/LiyNiO (colored)/electrolyte/NiO (bleached)/ITO (NiO//NiO) is studied. At 60 °C, the charge capacity of NiO//WO3 device increases from 2.59 mC/cm2 to 3.22 mC/cm2 compared with that at room temperature, and the chromaticity difference between colored and bleached state could reach ~36. When working at 80 °C, although the charge capacity of the device reaches 4.20 mC/cm2, the poor reversibility of the reaction of the NiO layer results in the irreversible attenuation of the device performance. Interestingly, after degradation associated with cycling at low temperature (56% capacity decrease at −10 °C), a recovery of the electrochromic properties at room temperature is observed. It can be considered that the low temperature within −10 °C basically has no non-recoverable damage to the devices. During the bleaching and coloring process, NiO layer mainly presents pseudocapacitance, while WO3 layer exhibits the ion diffusion control behavior (i.e, (de)insertion mechanism). A comparison with symmetrical devices, WO3//WO3 and NiO//NiO points out that performance change of complementary device NiO//WO3 is mainly affected by the cathodically colored electrochromic layer WO3.