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Öğe Cycling Durability of Electrochromic W-Ti Oxide Thin Films: Optical Transmittance Data Signal Dual Degradation Modes(Electrochemical Soc Inc, 2020) Sorar, Idris; Granqvist, Claes G.; Niklasson, Gunnar A.Electrochemical degradation of electrochromic W oxide and W-Ti oxide thin films, prepared by reactive DC magnetron sputtering, was studied by voltammetric cycling in potential intervals from 1.5-4.0 to 2.0-4.0 V vs Li/Li+ in an electrolyte of lithium perchlorate in propylene carbonate. Cycling-dependent evolution of the upper and lower limits for the optical modulation range was critically dependent on potential interval. This phenomenon was analyzed through an extension of a previously formulated model for power-law dynamics; it was discovered that the upper and lower limits for the optical modulation range varied in distinctly different ways, and that only data acquired in the interval 2.0-4.0 V vs Li/Li+ could be reconciled with dispersive chemical kinetics. We thus find that our data on optical transmittance degradation lends strong support to the existence of dual degradation modes for electrochromism upon extended electrochemical cycling. This result is of great importance for the development of highly durable electrochromic devices such as smart windows for energy-efficient buildings. The present article is a sequel to a recent publication of ours [J. Electrochem. Soc., 166, H795 (2019)]. (c) 2020 The Electrochemical Society (ECS). Published on behalf of ECS by IOP Publishing Limited.Öğe Durability and rejuvenation of electrochromic tungsten oxide thin films in LiClO4-propylene carbonate viscous electrolyte: Effect of Ti doping of the film and polyethylene oxide addition to the electrolyte(Elsevier, 2023) Sorar, Idris; Atak, Gamze; Pehlivan, Ilknur Bayrak; Granqvist, Claes G.; Niklasson, Gunnar A.Tungsten oxide and titanium doped tungsten oxide thin films, deposited by sputtering, were immersed in a viscous electrolyte comprised of LiClO4 in propylene carbonate and 2.0 wt% of polyethylene oxide (PEO). Electrochromic properties of the films were investigated by electrochemical techniques and in situ transmittance measurements. Cyclic voltammetry data were taken in the voltage ranges 2.0-4.0 and 1.5-4.0 V vs Li/Li+ for up to 500 cycles. A potentiostatic rejuvenation treatment was then performed on the degraded electrochromic films, at 6.0 V for 20 h, which was subsequently followed by another cyclic voltammetry measurement. Titanium incorporation into tungsten oxide resulted in a small cyclic stability improvement in the 2.0-4.0-V range, whereas less pronounced effects were observed for cycling in the 1.5-4.0-V range. Combining the results of the present study with our previous work, we are able to assess the relative merits of titanium incorporation and PEO addition to the electrolyte for the durability of electrochromic tungsten oxide thin films. Titanium addition was found advantageous for electrochemical durability in the 2.0-4.0-V range, but no clear benefits of PEO in the electrolyte were seen. On the other hand, in the wider 1.5-4.0-V range, tungsten oxide exhibited better durability than titanium-containing films, and this was especially so after rejuvenation in the PEO-containing electrolyte.Öğe Electrochromism in Ni Oxide Thin Films Made by Advanced Gas Deposition and Sputtering: A Comparative Study Demonstrating the Significance of Surface Effects(Electrochemical Soc Inc, 2020) Sorar, Idris; Welearegay, Tesfalem G.; Primetzhofer, Daniel; Osterlund, Lars; Granqvist, Claes G.; Niklasson, Gunnar A.Films of electrochromic Ni oxide, with thickness in the similar to 100-1000-nm range, were prepared by reactive advanced gas deposition (AGD) and, for comparison, also by reactive DC magnetron sputtering (MS). Voltammetric cycling was performed in an electrolyte of lithium perchlorate in propylene carbonate in the voltage range 2.0-4.1 V vs Li/Li+, and concurrent optical transmittance modulation was studied at a wavelength of 530 nm. For the thickest films, the optical modulation range was as large as similar to 54% and the maximum transmittance was similar to 82% for deposition by AGD, whereas the corresponding numbers were similar to 45% and similar to 87% for MS. Rutherford backscattering spectrometry together with measurements of film thickness demonstrated that the porosity of 400-500-nm-thick films made by AGD and MS were similar to 84% and similar to 45%, respectively. The charge exchange per mass unit was as high as 48-67 C g(-1) for samples made by AGD. The corresponding number was much lower for MS, namely 13-18 C g(-1). These results lend convincing support to the view that the electrochromism of Ni-oxide-based films in Li-ion-conducting electrolytes is dominated by surface effects. (C) 2020 The Electrochemical Society (ECS). Published on behalf of ECS by IOP Publishing Limited.Öğe Electrochromism of DC magnetron sputtered TiO2 thin films: Role of deposition parameters(Elsevier, 2013) Sorar, Idris; Pehlivan, Esat; Niklasson, Gunnar A.; Granqvist, Claes G.We performed a comprehensive study on the electrochromism in TiO2 thin films made by reactive DC magnetron sputtering and elucidated the roles of sputter gas pressure p, O-2/Ar gas ratio gamma and substrate temperature tau(s). Good mid-luminous optical modulation taken to be similar to 50% in similar to 200-nm-thick films was obtained under charge exchange in a Li+ electrolyte for p > 15 mTorr and tau(s) < 100 degrees C, whereas gamma was less important. The deposition rate dropped for increasing p, and hence p approximate to 15 mTorr was optimal. These films were X-ray amorphous and contained some water. The coloration efficiency eta was 25 cm(2)/C, which exceeds data on eta in most prior studies on sputter deposited TiO2 and verifies that such films can display the same values of eta as those of TiO2 films made by several chemical techniques. (C) 2013 Elsevier B.V. All rights reserved.Öğe Electrochromism of DC magnetron-sputtered TiO2: Role of film thickness(Elsevier Science Bv, 2014) Sorar, Idris; Pehlivan, Esat; Niklasson, Gunnar A.; Granqvist, Claes G.Titanium dioxide films were prepared by reactive DC magnetron sputtering and the role of the film thickness d on the electrochromism was analyzed for 100 < d < 400 nm. The best properties were obtained for the thickest films, which yielded a mid-luminous transmittance modulation of 58% and a corresponding coloration efficiency of 26.3 cm(2)/C. The films were amorphous according to X-ray diffraction measurements and showed traces of adsorbed water as revealed by infrared spectroscopy. (C) 2013 Elsevier B.V. All rights reserved.Öğe Electrochromism of W-In oxide thin films: Implications for cycling durability(Elsevier Science Sa, 2020) Sorar, Idris; Pehlivan, Ilknur Bayrak; Granqvist, Claes G.; Niklasson, Gunnar A.Electrochromic W oxide and W-In oxide thin films were prepared by dual-target reactive DC magnetron sputtering and were cycled voltammetrically in an electrolyte of lithium perchlorate in propylene carbonate. Film degradation was investigated for up to 500 cycles in the voltage ranges 1.5-4.0, 1.7-4.0 and 2.0-4.0 V vs. Li/Li+, and optical transmittance was recorded concurrently. Indium doping was found to be unambiguously detrimental to electrochromic cycling durability, which resolves an outstanding issue related to recently discovered unprecedented durability of potentiostatically pretreated W oxide films backed by In2O3:Sn and gives strong support in favor of beneficial effects of solid-electrolyte interfacial layers.Öğe Electrochromism of W-Ti Oxide Thin Films: Cycling Durability, Potentiostatic Rejuvenation, and Modelling of Electrochemical Degradation(Electrochemical Soc Inc, 2019) Sorar, Idris; Rojas-Gonzalez, Edgar A.; Pehlivan, Ilknur Bayrak; Granqvist, Claes G.; Niklasson, Gunnar A.Thin films of electrochromic W oxide and W-Ti oxide were prepared by reactive DC magnetron sputtering and were cycled voltammetrically in an electrolyte of lithium perchlorate in propylene carbonate. Film degradation was studied for up to 500 voltammetric cycles in voltage ranges between 1.5-4.0 and 2.0-4.0 V vs. Li/Li+. Optically and electrochemically degraded films were subjected to potentiostatic posttreatment at 6.0 V vs. Li/Li+ to achieve ion de-trapping and rejuvenation so that the films partly regained their original properties. Ti incorporation and potentiostatic posttreatment jointly yielded superior electrochromic properties provided the lower limit of the voltage range was above 1.6-1.7 V vs. Li/Li+. Degradation dynamics for as-deposited and rejuvenated thin films was modeled successfully by power-law kinetics; this analysis indicated coexistence of two degradation mechanisms, one based on dispersive chemical kinetics and operating universally and another, of unknown origin, rendered inactive by rejuvenation. The results of the present study are of large interest for the development of electrochromic devices with exceptional durability. (C) 2019 The Electrochemical Society.Öğe Potentiostatic rejuvenation of electrochromic WO3 thin films: Exploring the effect of polyethylene oxide in LiClO4-Propylene carbonate electrolytes(Elsevier, 2020) Sorar, Idris; Pehlivan, Ilknur Bayrak; Bohlin, Jan; Granqvist, Claes G.; Niklasson, Gunnar A.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.
