Sythesis And Photoelectrochemical Properties Of CdS Quantum Dots Sensitized Two-dimensional Nanostructure WO₃Films

Abstract:WO3is regarded as one of the most promissing photoelectric conversion materials because of its advantages such as high stability, non-poisonous and low price. However, the low light absorption and high charge recombination restrict its application. In this thesis, the quantum dots (QDs) sensitizing method and the metal elements doping method were utilized to extend WO3light absorption region, facilitate the separation of photo-generated electrons and holes, prolong the lifetime of charge carriers and improve photoelectrochemical performance of WO3thin films, providing a reference value for the application of WO3as photoelectric conversion material.The WO3nanoplate films were prepared by hydrothermal method. The CdS QDs sensitized WO3films were prepared by chemical bath deposition (CBD) method using ethanol solution containing Cd(NO3)2and methanol solution containing Na2S. The surface morphology, crystalline phase and surface chemical composition of the samples were characterized by field emission scanning electron microscope (FESEM), high resolution transmission electron microscopy (HRTEM), X-ray diffraction (XRD) and X-ray photoelectron spectroscope (XPS). The results indicate that CdS QDs deposited on the WO3nanoplate successfully when the integrity of WO3nanoplate remained unchanged. The WO3nanoplate is monoclinic phase and CdS QD is hexagonal phase. The average length, width and thickness of WO3nanoplate are approximately1μm,1μm and200nm respectively. The ultraviolet-visible absorption spectra (UV-Vis) shows that CdS QDs sensitized WO3film has a red-shift compared to bare WO3film. The photocurrent-potential curve, Mott-Schottky and electrochemical impedance spectroscopy (EIS) measurements imply that the density of charge carriers of CdS QDs sensitized WO3film increased obviously and the separation of photo-generated electrons and holes became fast. The photocurrent density of CdS QDs sensitized WO3film is7times higher than that of bare WO3film, increasing to1.12mA/cm2(0V, vs Ag/AgCl).Based on above, we prepared Mn2+doped CdS QDs sensitized WO3film using co-deposition method. In comparision with CdS QDs sensitized WO3film, the absorption edge of Mn2+doped CdS QDs sensitized WO3film is red-shifted, the density of charge carriers is increased and the separation efficiency of photo-generated electrons and holes is boosted. The photocurrent density increases to2.30mA/cm2at0V (vs. Ag/AgCl). The power conversion efficiency of quantun dots sensitized solar cells (QDSC) increases by83%using Mn2+doped CdS QDs sensitized WO3film as photoanode.