OFF five times in $\sim$100 seconds. It is worth mentioning that it takes more time in returning to OFF state after removal of the applied bias because the returning to OFF state is natural and is not under any external perturbation. A 50 % transparency in the second cycle onwards has been considered as OFF state whereas ON state corresponds to 100 % transparency. Additionally, contrast between the ON and OFF states can be calculated by defining colour contrast ratio (CCR) using the following equation\[35-–37\]. $$CCR(\%) = \frac{T_i-T_f}{T_i}\times 100$$

Here T$_i$ and T$_f$ are the initial and final values of transmittance for the device at wavelengths 580 nm. The values of T$_i$ and T$_f$ are 80% and 12% giving a 68% variation in transmittance and CCR of nearly 85%. Figure 6 also shows that it takes approximately 1.5 seconds to switch between the ON and OFF states of the device. An electrochromic device with 85% CCR is a very good device with an ability to switch in 1.5 seconds which can be improved if an external method is used for turning OFF the device of course by modifying the device composition and geometry appropriately.

Conclusions
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In-situ spectroscopic studies of 