Nd-Nb Co-doped SnO₂/α-WO₃ Electrochromic Materials: Enhanced Stability and Switching Properties

The fabrication of Nd-Nb co-doped SnO₂/α-WO₃ 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-WO₃ without causing much lattice strain due to the similar ionic radius of Nb⁵⁺ and W⁶⁺. 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 SnO₂, improving the electronic conductivity and easing the insertion and extraction of Li⁺ cations from the ECs. The enhanced Nd-Nb co-doped SnO₂/α-WO₃ 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 SnO₂/α-WO₃ presented in this work demonstrates an excellent candidate material for smart window applications to be used in green buildings.