Electrochromic smart windows that are able to dynamically control the light and heat transmission into a building have attracted intense interests in the field of green building. However, currently external energy consumption is required for electrochromic smart windows to change their optical properties such as transmittance, reflectance and absorption. How to recycle the energy expended and finely integrate the multifunctional smart window are still challenging at present. With our earlier established work on the various of electrochromic nanomaterials such as NiO, WO₃ on transparent conductors such as ITO, FTO, silver grid/PEDOT substrates, the importance and progresses of multifunctional smart window have been highlighted.^1-4 We extended our efforts on large size multifunctional smart windows (more than 300 cm²) fabricated by inkjet printing technique which is one of the low cost and solution processible methods. The assembled electrochromic windows exhibit outstanding performance including large optical modulation, high coloration efficiency, fast switching and excellent bistability. The designed multifunctional smart window can be used as typical electrochromic window as well as energy-storage device. The smart window is able to change its color to dynamically control the light and heat into a building and store the energy in the day time, and then releases the stored energy to power other electronic devices at night. Moreover, we can monitor the level of stored energy in the window via the visually detectable reversible color variation. The reported multifunctional smart window represents a leap towards the realization of fascinating and energy-efficient smart green building.

References (1) Cai, G.; Wang, X.; Cui, M.; Darmawan, P.; Wang, J.; Eh, A. L.-S.; Lee, P. S. Nano Energy 2015, 12, 258. (2) Cai, G.; Wang, J.; Lee, P. S. Acc. Chem. Res. 2016, 49, 1469. (3) Cai, G.; Darmawan, P.; Cui, M.; Chen, J.; Wang, X.; Eh, A. L.-S.; Magdassi, S.; Lee, P. S. Nanoscale 2016, 8, 348. (4) Cai, G.; Darmawan, P.; Cui, M.; Wang, J.; Chen, J.; Magdassi, S.; Lee, P. S. Adv. Energy Mater. 2016, 6, 1501882.