Terpolymer based gel electrolytes: Augmented redox couple diffusion via iodide salts and copper(II) oxide nanofiller for dye-sensitized solar cells / Nur Khuzaimah Farhana Abd Aziz

Nur Khuzaimah Farhana , Abd Aziz (2022) Terpolymer based gel electrolytes: Augmented redox couple diffusion via iodide salts and copper(II) oxide nanofiller for dye-sensitized solar cells / Nur Khuzaimah Farhana Abd Aziz. PhD thesis, Universiti Malaya.

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Abstract

Dye-sensitized solar cell (DSSC) has received widespread attention for its low-cost, environmental benignity and potential high conversion efficiency as compared to conventional silicon solar cells. The utilization of liquid electrolyte in DSSCs is often associated with several practical issues such as electrolyte leakage and evaporation, and precipitation of salts in polymer at low temperature which make gel polymer electrolyte (GPE) is preferable. Gel polymer electrolytes (GPEs) consisting of terpolymer, poly(vinyl butyral-co-vinyl alcohol-co-vinyl acetate) (P(VB-co-VA-co-VAc)) and different compositions of iodide salts (sodium iodide, NaI and tetrapropylammonium iodide, TPAI) have been prepared and investigated. Host polymer-salt complex suffers from low ionic conductivity and poor mechanical strength due to slow ion mobility within the polymer system. Incorporating metal oxide nanofiller into GPE is one of the approaches that can be used to obtain improvement in ionic conductivity and efficiency due to their large surface area which provides cross linking centers for the polymer segment. Copper oxide (CuO) nanofillers were synthesized through sonochemical method and subsequently calcination at different temperatures (200 ℃, 350 ℃ and 500 ℃). These nanofillers were incorporated into the GPE to form polymer composite gel electrolyte (PCGE). Then, different amounts of CuO-350 nanofiller (CuO nanofiller calcined at 350 ℃) were added to the best polymer-salt system sample. The results of X-ray diffraction (XRD) were utilised to explain the trend in ionic conductivity obtained when increasing the amounts of NaI salt, TPAI salt, and CuO nanofillers. Fourier transform infrared spectroscopy (FTIR) measurements have confirmed the complexation of chemicals inside the electrolyte. The electrochemical performance of GPE was investigated using electrochemical impedance spectrometry (EIS) and linear sweep voltammetry (LSV). It was found that NaI-3 and TPAI-4 exhibited the highest ionic conductivity of ((3.22 ±0.01) × 10−3 S cm-1 and ((1.93 ±0.01) × 10−3 S cm-1) and apparent triiodide diffusion coefficient (3.25 × 10−6 cm2 s −1 and 5.96 × 10-6 cm2 s-1) in polymer-salt system, respectively. The addition of CuO-350 nanofillers has enhanced the ionic conductivity and apparent triiodide diffusion coefficient of the TCuO350-3 sample to (3.49 ±0.01) × 10−3 S cm-1 and 1.48 × 10-5 cm2 s-1, respectively. On the other hand, the developed GPEs and PCGEs were used to fabricate DSSC. For the salt-based GPE, the highest efficiency of 4.62 % was achieved by TPAI-4 system compared to NaI-3 system with the efficiency of 4.01 % due to the higher diffusion coefficient of the redox couple. By adding CuO-350 into the polymer-salt system, the efficiency increased to 7.05 %. The longer rod structures of CuO-350 provide a continuous path for redox couple diffusion than other calcination temperature nanofiller. The best sample among PCGE is TCuO350-3. It has 5 wt. % of CuO-350 and an efficiency of 7.69 % with JSC of 23.47 mA cm-2, VOC of 0.62 V, and fill factor of 52.9 %.

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