Molybdenum‐Doped Nickel Oxide as an Advanced Ion Storage Layer for Highly Stable and Durable Flexible Electrochromic Devices

Abstract Electrochromic (EC) smart windows, typically consisting of a monolithic transparent conductive oxide (TCO), an EC layer, an electrolyte, and an ion storage layer are promising technologies for improving energy efficiency, enhancing environmental sustainability, and regulating solar heat gain, thereby supporting occupant‐centric reductions in carbon emissions. However, the conventional nickel oxide (NiO) ion‐storage layer, faces significant challenges such as rapid cycling degradation and limited mechanical flexibility, hindering its application in flexible devices. In this study, a highly stable and flexible molybdenum‐doped nickel oxide (Mo‐doped NiO, MNO) ion‐storage layer deposited on a polyethylene terephthalate (PET) substrate coated with a TCO layer of indium gallium titanium oxide (IGTO) using a co‐sputtering technique is presented. The MNO thin film exhibits excellent EC performance, transitioning from an initial dark brown state to a transparent state upon applied voltage. The electrical properties of the MNO film exhibits enhanced EC performance compared to pristine NiO. Furthermore, the MNO film demonstrates superior cycling stability, maintaining its performance over 500 operational EC cycles. It also retain electrical stability after inner and outer bending, exhibiting negligible changes in resistance even after 10,000 cycles. A potential Mo‐doping mechanism to explain the enhanced stability of the MNO‐based flexible EC devices is proposed. These findings highlight the potential of MNO as a superior alternative to conventional NiO for advanced EC technology and smart windows.