Synthesis of zinc selenide quantum dots by successive ionic layer adsorption and reaction (silar) method for quantum dot sensitized solar cells (qdssc)
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Date
2018-06
Authors
Chang, Wan Ling
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Abstract
Quantum dot sensitized solar cells (QDSSCs) have been intensively concerned in the
past decades. Zinc selenide (ZnSe) is an alternative material to replace toxic cadmium-based
quantum dots (QDs). In this research, ZnSe QDs were deposited on TiO2 electrode as TiO2
photoanode using successive ionic layer adsorption and reaction (SILAR) method for
QDSSCs. TiO2 electrode was formed with the deposition of TiO2 mesoporous film on
fluorine doped tin oxide (FTO) glass after the sintering in furnace at 370 °C for 10 minutes,
the temperature was increased to 450 °C and held for 30 minutes. Solar cells were prepared
by sandwiching the TiO2 photoanode and Cu2S counter electrode with polysulfide
electrolyte in the between. Effect of fluoride treatment on TiO2 mesoporous film prior to
deposition of ZnSe QDs, number of SILAR cycles (5, 10, 15, 20 and 25), molar
concentration of zinc acetate dihydrate solution (0.03 M, 0.05 M, 0.1 M, 0.3 M and 0.5 M),
and the effect of ZnS blocking layer coating after ZnSe layer was studied. The samples were
prepared and characterized with X-ray diffraction (XRD), field emission scanning electron
microscope (FESEM), energy dispersive X-ray spectroscopy (EDX), high resolution
transmission electron microscope (HRTEM), atomic force microscope (AFM), UV-visible
(UV-vis) spectroscopy, and current density-voltage (J-V) measurement. ZnS blocking layer
was found that did not contribute in improving the efficiency of QDSSCs due to its wide
band gap of 3.10 eV. Generally, as number of SILAR cycles and molar concentration of XXIV
precursor solution increased, the efficiency increased due to more and bigger ZnSe nuclei
were formed in the TiO2 mesoporous film. However, pore-blocking on the TiO2 mesoporous
structure may occur due to overloading of QDs. Sample with 20 SILAR cycles shows the
highest efficiency of 0.6988 % while deposition using 0.1 M zinc acetate dihydrate solution
shows efficiency of 0.5956 %. The sample with fluoride treatment on TiO2 mesoporous film
also shows the higher efficiency of 0.4485 % than without fluoride treatment of 0.0679 %.
In this research, the results can be concluded to suggest to carry out fluoride treatment on
TiO2 mesoporous film prior deposition of 20 SILAR cycles of ZnSe QDs with 0.1 M of zinc
acetate dihydrate solution.