Citation

Au, Benedict Wen Cheun (2022) Investigation of electrochromic performance of WO3 films based on liquid and gel electrolytes. PhD thesis, Multimedia University.

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Abstract

Electrochromism is the phenomena of inducing a reversible optical change (colouring and bleaching) in electrochromic (EC) materials under the influence of a small electric field. It has become increasingly important in energy-saving applications such as smart windows in smart buildings which are in line with the rapid expansion of Internet of Things. In this thesis, EC tungsten oxide (WO3) films were fabricated on indium doped tin oxide (ITO) coated glasses via the sol-gel spincoating technique. The influence of film thickness, structural properties, precursor solution stirring time and varying electrolyte on the EC properties of WO3 films were studied and elucidated. In the investigation of film thickness effect, different number of layers of WO3 films was deposited on ITO coated. XRD results revealed the amorphous nature of the WO3 films in thinner films and polycrystalline nature in thicker films. Surface properties in thinner films showed smooth and compact surface which revealed its amorphous nature. Thicker films had randomly oriented rectangular shape grains on WO3 film surface. CV results showed increase in diffusion coefficient with increasing film thickness. CA results showed increased in both colouring time and bleaching time as more time is needed for the insertion and extraction of ions in thicker films. Furthermore, simultaneous transmittance results from CA recorded largest optical modulation of 40 % at 338 nm with a corresponding colouration efficiency (CE) of 34.8 cm2 /C. Sol-gel spin-coated WO3 films were heat treated at temperatures ranging from 27 °C to 450 °C for the study of post-annealing effect. The increasingly prominent monoclinic peaks in the XRD spectra indicated the amorphous-to-crystalline transition of the WO3 films. Uniform and smooth surfaces were observed in WO3 films annealed at lower temperatures while higher temperature resulted in denser films. CV results revealed decreased diffusion coefficient in denser WO3 films. Besides that, the colouration and bleaching kinetics reduced with increasing postannealing temperature. WO3 films heat treated at 250 °C exhibited a good balance among ion storage capacity, high optical modulation and CE. WO3 precursor solutions were prepared via the sol-gel spin-coating method where the stirring time was varied between 3 h, 10 h and 24 h (W-3, W-10 and W24). The W-3 film appeared to be clear and highly transparent, W-10 film appeared to be fairly transparent but with a slightly greyish surface and the W-24 film appeared to have a dark grey surface with low transparency. Optical properties showed W-3, W-10 and W-24 exhibited 80 %, 70 % and 15 %, respectively in the visible range. CV results revealed highest colouration current in W-3 which indicated faster intercalation kinetics compared to W-10 and W-24. Besides that, W-3 exhibited largest optical modulation of 40 % and subsequently high CE of 34.8 cm2 /C. Lithium iodide in polyethylene glycol (PEG:LiI) and lithium perchlorate in propylene carbonate (PC:LiClO4) polymer electrolytes were investigated for its influence on the EC properties of sol-gel deposited WO3 films. CV results revealed greater diffusion coefficient of W:ClO4 films compared to W:I. CA results revealed quicker switching characteristics in W:ClO4. Optical properties revealed higher optical modulation of 36 % in W:ClO4 compared to the 28 % in W:I which led to a CE of 18.72 cm2 /C and 16.70 cm2 /C, respectively. Solid polymer electrolyte (SPE) and liquid polymer electrolyte (LPE) were investigated for its EC performance in WO3 based ECDs fabricated on ITO. CV voltammogram showed larger diffusion coefficient in LECD compared to SECD. In contrast, the optical modulation of SECD was found to be slightly greater than LECD in the visible range. Along with it, CA results showed W:ClO4 exhibited more rapid colouring time compared to W:I with a similar bleaching time. Thereafter, the CE for LECD was found to be higher than that of SECD. In the study of different TCOs on the performance of ECDs, WO3 films were spin-coated on ITO and fluorine doped tin oxide (FTO) coated glass. Thereafter, they were assembled into ECDs with ITO and aluminium doped zinc oxide (AZO), respectively as counter electrodes. CV results showed greatest diffusion coefficient for ECD(F:A) while ECD(I:A) and ECD(I:I) had lower diffusion coefficient. CA results revealed large optical modulation of 42 % in ECD(F:I) which led to a high CE of 72.5 cm2 /C.

Item Type:	Thesis (PhD)
Additional Information:	Call No.: TK8360.E44 A99 2022
Uncontrolled Keywords:	Electrochromic devices
Subjects:	T Technology > TK Electrical engineering. Electronics Nuclear engineering > TK7800-8360 Electronics > TK8300-8360 Photoelectronic devices (General)
Divisions:	Faculty of Engineering (FOE)
Depositing User:	Ms Nurul Iqtiani Ahmad
Date Deposited:	28 Nov 2023 04:12
Last Modified:	28 Nov 2023 04:12
URII:	http://shdl.mmu.edu.my/id/eprint/11872

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