A layer-stacked NiO nanowire/nanosheet homostructure for electrochromic smart windows with ultra-large optical modulation.

The structural engineering of active materials at the nanoscale level is crucial to improving the performance of electrochromic devices. However, an insufficient structural design inevitably results in limited electron/ion transportation and inadequate electrochromic performance. Herein, a new type of layer-stacked nanowire/nanosheet homostructure is proposed for enhancing the electrochromic properties of transition metal oxide films. Benefiting from the one-pot feature integration of nanowire and nanosheet structures, the NiO film with a unique homostructure delivers ultra-large optical modulation up to 93.4% at 550 nm and a high coloration efficiency of 72.1 cm C in comparison with NiO-based materials. In addition, the film maintains 91% of its optical modulation over 1000 cycles of coloration and bleaching processes. Furthermore, the high performance of the device was verified by integrating the NiO film with the TiO ion storage layer in assembled smart windows with a dual function of electrochromic and energy storage. As a proof of concept, the integration of solar cells with electrochromic devices demonstrates the great significance of self-powered smart windows for energy-saving. To this end, such a strategy of structural design for electrochromic films would offer a distinctive pathway toward studying high-performance electrochromic systems.