Nd-Nb Co-doped SnO/α-WO Electrochromic Materials: Enhanced Stability and Switching Properties.

The fabrication of Nd-Nb co-doped SnO/α-WO electrochromic (EC) materials for smart window applications is presented in the present paper. Nb is a good dopant candidate for ECs owing to its ability to introduce active sites on the surface of α-WO without causing much lattice strain due to the similar ionic radius of Nb and W. These active sites introduce more channels for charge insertion or removal during redox reactions, improving the overall EC performance. However, Nb suffers from prolonged utilization due to the Li ions trapped within the ECs. By coupling Nd with Nb, the co-dopants would transfer their excess electrons to SnO, improving the electronic conductivity and easing the insertion and extraction of Li cations from the ECs. The enhanced Nd-Nb co-doped SnO/α-WO exhibited excellent visible light transmission (90% transmittance), high near-infrared (NIR) contrast (60% NIR modulation), rapid switching time (∼1 s), and excellent stability (>65% of NIR modulation was retained after repeated electrochemical cycles). The mechanism of enhanced EC performance was also investigated. The novel combination of Nd-Nb co-doped SnO/α-WO presented in this work demonstrates an excellent candidate material for smart window applications to be used in green buildings.