The effects of lithiation process on the performance of all-solid-state electrochromic devices

All solid-state electrochromic devices were fabricated using radio-frequency magnetron sputtering. The electrochromic layers employed in the all solid-state device were subjected to lithiation insertion to improve performance of the device. Two structures, one with dry, and one with both wet and dry lithiation processes were used for intercalation of lithium atoms into the electrochromic layers. The main device configuration was as follows: indium tin oxide (ITO)/NiO/Ta2O5/dry lithiated WO3/ITO/glass. Dry lithiation was performed by exposing the WO3 layer in vacuum to Li vapor atoms obtained by radio-frequency (RF) magnetron sputtering of LiNbO3 at room temperature. An additional, wet lithiation, step was performed on one structure by electrochemical cycling in a solution containing lithium ions, leading to Li+ insertion into the Ta2O5 layer used as an ion-conducting layer. The optical modulation of the device containing only dry lithiated WO3 was found to be 34.8% at 550 nm for applied potentials of ±4 V. With wet lithiation additionally applied to the ion-conducting layer (Ta2O5), the optical modulation of the device increased to 71.7% at 550 nm for applied potentials of ±4 V.