Fig. 1: Four modes of complementary electrochromic device (ECD) controlled by co-intercalation of both anions and cations.

a Bright blue, as assembled. b Transparent, under a positive bias. c Dark blue, under a negative bias. d Green, under a negative bias. The insets are digital images of the device and the diagrams for different states of Nb₁₈W₁₆O₉₃ and PB films. e Transmittance spectra of the device in the wavelength range of 400–2200 nm. The bias for the marked modes is OCP (bright blue), 1.5 V for 30 s (transparent), −1.8 V for 30 s (dark blue), and −2.4 V for 30 s (green), respectively. f Solar irradiance of the device in different modes in the wavelength range of 400–2200 nm. g Commission Internationale de l´Eclairage (CIE) chrominance coordinates L*, a* and b* in the CIELAB color space of the device at marked modes. h In-situ transmittance variation of the device under square-wave (−2.5 V for 20 s and 1.5 V for 20 s) cycling. i Changes in the optical density at 633 nm with respect to the intercalated charge density. j Cycling performance of the device under the square-wave (−2.3 V for 15 s and 1.3 V for 15 s) cycling for 6000 cycles. Chronoamperometry curves for (h) and (j) are shown in Fig. S4. The inset shows the transmittance at the 10th, 2000th, 4000th and 6000th cycles. All the transmittance data were recorded at 633 nm.