Tristate Electrochromic Device Enabling Transparent–Black–Yellow Switching via Metal/Nonmetal Synergistic Deposition

Reversible metal electrodeposition has attracted extensive attention for its ability to achieve color–neutral switching between transparent and black states; however, its color expression remains relatively limited, making it difficult to meet the demand for versatile color modulation. This work proposes a hybrid deposition strategy that combines metal and nonmetal redox processes in a single electrochromic device. The metal component involves codeposition of Cu 2+ and Bi 3+ ions for high‐contrast black‐state formation, while the nonmetal component utilizes reversible Br − /Br 3 − conversion. Br 3 − is further stabilized via complexation with 1‐methyl‐3‐propylimidazolium ion (MPI + ) to form yellow MPIBr 3 , enabling a transparent‐to‐yellow transition. These two processes are synergistically driven and precisely controlled by applied voltages, allowing reversible switching among transparent, black, and yellow within a single device. The device exhibits a high optical modulation of up to 60.8% in the yellow state, and the transmittance can be modulated below 1% in the black state, demonstrating excellent color neutrality and privacy protection. Moreover, after 24 h of resting, the transmittance increases by only 1.3%, indicating outstanding open‐circuit stability. This multicolor dynamic switching capability not only fulfills the functional requirements of smart windows for privacy and light regulation but also offers enriched color expression of aesthetic value.