The Effect of Alkali Metal (Na, K) Doping on Thermochromic Properties of VO2 Films

This work reports the synthesis of undoped and alkali metal doped thermochromic vanadium dioxide thin films by sol-gel spin coating and subsequent low-temperature annealing at 450 °C in N 2 -H 2 atmosphere. The effect of sodium and potassium on the phase transition temperature as well as on the solar modulations were investigated. A dopant concentration of 0.3 at% resulted in a reduction of the critical transition temperature (T c ) from 62 °C to 57 °C and 47 °C for the sodium and potassium doped films, respectively. Moreover, both dopants improved the solar modulations (ΔT sol ) of the undoped VO 2 films from 3.81 to 9.44 and 5.43 %, respectively.