Performance specific recipe for nano-Co3O4 based electrochromic electrodes: Optimizing color modulation parameters

The development of smart windows requires highly efficient electrochromic electrodes with fast response time and high optical modulation hence material synthesis parameters need to be optimized to get a material to give best possible performance. In this work, a set of Co₃O₄ films was prepared by electrodeposition in a constant current mode where the concentration of NaNO₃ and annealing temperatures were kept as variables. All the Co₃O₄ films exhibited noticeable bias induced color modulation from yellow to brown, which is characterized using bias-dependent in-situ transmission spectroscopy. An optical-modulation of 64 % (at 650 nm) could get observed for the Co₃O₄ films prepared using 0.05 M NaNO₃ and annealed at 250 °C. A very fast response time of 2.2 s/1 s for switching from colored to bleached state and vice versa. The coloration efficiency was 58.9 cm²/C for Co₃O₄ films synthesized using 0.05 M NaNO₃ and annealed at 150 °C, due to the electrode's highly porous nature. These enhancements make cobalt oxide electrodes a suitable choice as an anodic electrode for designing solid-state electrochromic devices in real-life applications. A recipe for designing a performance based electrochromic smart film has been obtained based on the correlation between the deposition parameter and their electrochromic performance.