Electrochromism of W–Ti Oxide Thin Films: Cycling Durability, Potentiostatic Rejuvenation, and Modelling of Electrochemical Degradation

Abstract

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Cycling Durability of Electrochromic W-Ti Oxide Thin Films: Optical Transmittance Data Signal Dual Degradation Modes

“…We hypothesize that the deviations may be connected with variations in coloration efficiency at low cycle numbers that were observed previously, 14 or that they may indicate a more complex degradation process than assumed in Eq. 4.…”

“…20 Specifically, this parameter can be estimated from y = QM/(eAdρNA), where M is molar mass of a formula unit of the oxide, e is elementary charge, A is sample area, ρ ≈ 5.5 g cm -3 is film density, 21 and NA is Avogadro's constant. The maximum charge exchange in our samples occurs for a WO3 film subjected to treatment in the potential range 1.5-4.0 V. 14 The analysis delineated above indicates that site saturation would be important primarily in the initial CV cycles for the widest potential ranges, i.e., when the charge exchange is very high, and be most significant in the case of the WO3 films. We thus write…”

“…These parameters are reported in Table 1 for the various samples and potential ranges; also included are data on 𝑝 𝑄 as derived from charge density evolution in our earlier work. 14 A number of observations can be made from Table 1: Firstly, it is seen that pc ≈ pQ, which indicates that critical exponents for degradation of electrochromic films indeed can be derived conveniently from optical transmittance evolution and do not have to rely on more complicated charge-density measurements. This result also indicates that the deviations between experimental data and our degradation model do not significantly influence the evaluation of Tc data.…”

“…These are the situations wherein site saturation is predicted to be most significant. The exchanged charge increases considerably with the width of the potential interval, 14 and the addition of Ti could delay the onset of site saturation since Ti oxide also colors in the considered potential intervals. Interestingly, the deviations are absent in the potential range 2.0-4.0 V and are not significant for the sample with the highest Ti content.…”

Differential coloration efficiency of electrochromic amorphous tungsten oxide as a function of intercalation level: Comparison between theory and experiment

“…[13], and Ref. [14], respectively. The present work differs from the previous approaches because it makes use of the differential coloration efficiency, defined as the derivative of the optical density with respect to the inserted charge.…”