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.National Research Foundation (NRF)Published versionThis research was supported by grants from the National Research Foundation, Prime Minister’s Office, Singapore, under its Campus of Research Excellence and Technological Enterprise (CREATE) Program

Novel Nd–Mo co-doped SnO₂/α-WO₃ electrochromic materials (ECs) for enhanced smart window performance

In an urbanized city, about a third of total electrical consumption is allocated for indoor lighting and air conditioning system in residential and commercial buildings. The majority of the worldwide energy generation comes from burning of non-renewable fossil fuel which is not sustainable in the long run. The use of smart windows technology may catalyze the effort to reduce energy consumption of building and houses. More than 50% of heat entering a building through windows originate from the solar radiation in the near infrared (NIR) region. This candidate smart window material must exhibit dual-band (visible and NIR) modulation that allows selective modulation of NIR heat without affecting visible light transmission. A good electrochromic material in this respect should possess high visible light transmission, high NIR modulation, fast switching between colored and bleached state, and good stability over prolonged usage. In this work, we propose a novel Nd–Mo co-doped SnO2/α-WO3 electrochromic materials (ECs). As compared to the traditional SnO2/α-WO3 ECs, our Nd–Mo co-doped SnO2/α-WO3 ECs exhibits up to 90% visible light transparency (at λ = 600 nm), 62% NIR modulation (at wavelength 1200 nm), high coloration efficiency (~200 cm2 C−1), fast switching time with only 31% electrochromic performance drop (vs 59% of undoped sample) after up to 1000 reversible cyclic test. The enhanced electrochromic performance comes from the presence of Nd–Mo co-dopants that limit the trapping of Li + ion within α-WO3 framework, reduce the extent of crystallization of α-WO3 layer and enhancement of the electronic conductivity by transferring their excess electron to the conduction band of the SnO2. To the best of the authors’ knowledge, the present composition of ECs offers one of the better candidate materials for electrochromic to be used as thermal management layers on smart windows application.National Research Foundation (NRF)This research is supported by grants from the National Research Foundation, Prime Minister’s Office, Singapore under its Campus of Research Excellence and Technological Enterprise (CREATE) Program