In situ colorimetric and composite coloration efficiency measurements for electrochromic Prussian blue

Abstract

An in situ colorimetric method, based on the CIE (Commission Internationale de l'Eclairage) system of colorimetry, has been successfully applied to the study of electrochromism in electrochemically deposited films of Prussian blue (iron(III) hexacyanoferrate(II), PB) on transmissive ITO/glass substrates for the first time. On electrochemical reduction of PB to Prussian white (iron(II) hexacyanoferrate(II), PW), sharp and reversible changes in the hue and saturation occur, as shown by the track of the CIE 1931 xy chromaticity coordinates. For PB, the CIELAB 1976 colour space coordinates were L* 5 73, a* 5 226 and b* 5 233, with a dominant wavelength calculated as 488 nm. Concurrently, as the intensely absorbing PB mixed-valence chromophore is 'bleached' to the transparent PW, a large increase in the relative luminance of the electrochromic film is observed. On oxidation of PB, the CIELAB 1976 colour space coordinates show the transition through intermediate green to the Prussian yellow (iron(III) hexacyanoferrate(III), PY) state (L* 5 94, a* 5 2 and b* 5 18), with a steady increase in relative luminance. To reliably compare the power requirement of PB films with other electrochromic systems, composite coloration efficiencies (CCE's) have been calculated, using a tandem chronoabsorptometry/chronocoulometry method, as previously developed for organic polymer systems. Using 95% of the total transmittance change at l max as reference point, coloration efficiencies, g 5 DA(l max )/Q, were calculated as 143 and 150 cm 2 C 21 respectively for the PB/PW and PW/PB electrochromic transitions.

Current status of some electrochromic materials and devices: a brief review

“…The device takes only 1.5 s to switch from its greenish to yellowish color and then reverses back to its greenish appearance such that there is 80% absorbance change, as observed from figure 6(c). It has a coloration efficiency of 246 cm 2 C −1 , as calculated using equation ( 5) and as shown in figure 6(d), which is quite impressive in the field of all inorganic ECDs [111,114,116,[118][119][120]. Here, it is mainly the robust behavior of inorganic EC materials that has been exploited with some compromise in efficiency.…”

“…From the above discussion, it is clear that like the Co 3 O 4 /EV device, the studied PB-EV blend can be used very efficiently in ECDs with good cycle life, switching time and CC for a power-efficient improved colormodulating device compared to any device containing PB [114,116,119,120,159].…”

“…Bottlenecks like limited stability and poor contrast, largely associated with charge-balancing issues, can be removed for potential application after just a few modifications to some parameters to some extent [113][114][115]. For this, an electrodeposition technique is used to deposit PB film over an ITO electrode, in which a blue-colored film is obtained and analyzed using the different experimental techniques discussed previously [116].…”

Electrochromism in Isoreticular Metal–Organic Framework Thin Films with Record High Coloration Efficiency

“…Encouraged by their easy preparation, uniform thin-film growth, and well-separated electrochemical and spectral features, the isoreticular MOFs were further evaluated for practical electrochromic applications. An important parameter in this context is the coloration efficiency (η, also known as electrochromic efficiency), which is a measure of the difference in absorptivity of two states, normalized to the charge that was required to induce the change. − Coloration efficiencies for all processes in the isoreticular MOF series were determined using the following eq : η = normalΔ normalO normalD Q where ΔOD is the change in optical density (between colored and bleached state) and Q is the corresponding charge density (C cm –2 ) used to induce the change in redox state (more details in the SI). Most notably, the η of the Zn-PDI film reaches 941 ± 35 cm 2 C –1 at 746 nm (Figure a), which to the best of our knowledge, is a record-high value reported in MOFs (see Table S3).…”

Visible Light Modulation Using Chemically Deposited Electrochromic Thin Films

“…In order to examine the time response (coloring and bleaching times), the transmittance at 550 nm was measured trough the ECTD (Fig. 8) [19] and [20] for WO3 films, and [21] for PB films. …”