Hierarchical core–shell structural based on WO3@ITO nanorods with boosted electrochromic performance in NIR region

Over half of the solar energy comes from the infrared region, which makes electrochromic materials that modulate infrared transmittance essential for the thermal management of smart windows. However, existing electrochromic materials do not perform well in the near-infrared region, which exhibits slow response time, weak adhesion to conductive substrates, and poor long-term cycling stability. In the present work, we successfully synthesized WO 3 @ITO nanorod samples with hierarchical core–shell structure by hydrothermal and in-situ solvothermal methods. ITO-coated WO 3 nanorods and some ITO nanocrystals were firmly integrated with WO 3 nanorods, resulting in a corn-like hybrid heterogeneous structure. The unique WO 3 @ITO hierarchical core–shell structure improves the electronic properties and the adhesion to substrates, reducing the energy barrier of ion diffusion and increasing the ion flux. Enhanced electrochromic performance in NIR range with a high optical modulation of 53.3 % in 1600 nm and long-term reversibility (maintaining 91.5 % of its original contrast after 1000 cycles) was achieved. In addition, response time (t c  = 3.5 s, t b  = 4.6 s) and coloration efficiency (112.5 cm 2 ‧C -1 ) have been significantly improved, which is almost twice that of unmodified WO 3 nanorods (t b  = 8.6 s and CE = 56.4 cm 2 ‧C -1 ), showing a good application prospect in smart windows.