WO 3 is the state of the art of electrochromic oxide materials finding technological application in smart windows. In this work, a set of WO 3 thin films were deposited by magnetron sputtering by varying total pressure, oxygen partial pressure, and power. On each film two properties were measured, the electrochemical reversibility and the blue color persistence of Li x WO 3 films in simulated ambient conditions. With the help of machine learning, prediction maps for such electrochromic properties, namely, color persistence and reversibility, were designed. High-performance WO 3 films were targeted by a global score which is the product of these two properties. The combined approach of experimental measurements and machine learning led to a complete picture of electrochromic properties depending of sputtering parameters providing an efficient tool in regards to time saving.

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Despite the long-standing history of electrochromism, there is a lack of universally accepted methods for quantitatively comparing cycling stability between different electrochromic materials or devices. By proposing a straightforward three-step procedure, we report a simple set of parameters that describe the cycling stability performance the most frequently used electrochromic materials, namely, conducting polymers, transition metal oxides, metallo-supramolecular polymers, and viologens. The main highlights of this procedure are an adequate definition of the testing conditions and the analytical description of the evolution of the performance of materials through continuous cycling. The resulting parameters allow us, not only to perform comparative studies among different materials and devices but also to identify tendencies, and therefore establish the corresponding balance, between the testing conditions and the cycling stability and/or optical performance obtained. This method constitutes a powerful decision-making tool for the academic and industry-related electrochromic community.

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