Potentiostatic rejuvenation of electrochromic WO3 thin films: Exploring the effect of polyethylene oxide in LiClO4-Propylene carbonate electrolytes

• Published in: Solar energy materials and solar cells 2020-12, Vol.218, p.110767, Article 110767
• Main Authors: Sorar, Idris, Bayrak Pehlivan, İlknur, Bohlin, Jan, Granqvist, Claes G., Niklasson, Gunnar A.
• Format: Article
• Language: English
• Subjects: Charge density; Cycles; Electric potential; Electrochemical degradation; Electrochromism; Electrolytes; Energy efficiency; Expulsion; Glazing; Light penetration; Lithium perchlorates; Magnetron sputtering; PEO; Polyethylene; Polyethylene oxide; Polymers; Potentiostatic rejuvenation; Propylene; Thin films; Tungsten oxide; Voltage; Voltammetry
• ISSN: 0927-0248; 1879-3398
• DOI: 10.1016/j.solmat.2020.110767

Thin films of electrochromic (EC) W oxide were prepared by reactive DC magnetron sputtering and were immersed in electrolytes of LiClO4 in propylene carbonate with 0.5–3.0 wt% of added polyethylene oxide (PEO). Charge density and optical modulation range were found to diminish monotonically upon prolonged voltammetric cycling with concurrent optical transmittance measurements for up to 500 and 200 cycles in the voltage ranges 2.0–4.0 and 1.5–4.0 V vs. Li/Li+, respectively. Rejuvenation of the degraded EC films was then accomplished by potentiostatic treatment at 6.0 V vs. Li/Li+ for 20 h and has been ascribed to expulsion of trapped Li ions. Importantly, degradation subsequent to rejuvenation was found to progress at a significantly lowered pace than for as-deposited films—in proportion with the amount of PEO—especially for harsh voltammetric cycling in the voltage range 1.5–4.0 V vs. Li/Li+. The results of this explorative study are of considerable value for the development of highly durable EC devices such as polymer-laminated smart glazing for energy efficient buildings with excellent indoor comfort. •Potentiostatic rejuvenation of electrochromic WO3 thin films was studied.•Films were immersed in electrolytes of LiPC with 0.5–3.0 wt% of added polyethylene oxide.•Film degradation was investigated in potential ranges of 1.5–4.0 and 2.0–4.0 V vs. Li/Li+.•The addition of PEO led to significant improvements of stability in the potential range 1.5–4.0 V.•Optical properties after rejuvenation are best for PEO concentrations in the range 1.5–2.5 wt%.