Tungsten oxide thin film memory storage time means tungsten oxide thin film can stay at coloring state after losing added voltage. It shows the quality of electrochromic device and capacity of saving energy.
By testing memory storage time of samples after coloring, with the rising annealing temperature, the memory storage time decreases. After annealing under 100 degree Celsius, the memory storage time is at least 72 hours, the maximum time may be one week. Annealing under 200 degree Celsius, the memory storage time is around 48 hours, under 300 degree Celsius the storage time is only 1 hour.
Coloring state film will fade after the applied voltage is lost which is because during the coloring process, ions and electrons gathered in the vicinity of a large number of both electrodes which forms a force opposite to the driving voltage. After cutting the power off, the driving voltage disappears, the electromotive force persists and begins to function. Its direction is the same with fading voltage which results in a discharge fading. With the decrease of counter electric force, the fading is almost stable. The exist of counter electric force is the reason why the coloring state reaction time is longer than fading state.