Preparation Of CuS, Bi₂S₃ Thin Films By In-situ Chemical Reaction Process And Photovoltaic Characterization Of Sensitized TiO₂ Solar Cells

Solar cell has drawing increasing attension of reseachers due to its cleaness and non-pollution. In the paper, the progress history, classification, structure, principle, current situation and existing problems of solar cells are reviewed in detail. At present, there are still some technical issues for solar cells, such as low photoelectric conversion efficiency, high production cost and environmental pollution.As non-toxic semiconductor materials, CuS and Bi₂S₃ have bulk band gap of 2.2 eV and 1.3 eV, respectively, which provide promising potential for photovoltaic applications owing to their excellent optical, electrical and photoelectrochemical properties. At present, chemical bath deposition（C BD） and successive ion layer adsorption and reaction method（SILAR） have been widely used in deposition of metal sulfide thin films. However, CBD technique has the disadvantages on serious loss of ionic precursor sources and up- limitation of film thickness. And SILAR has low growth rate of thin film thickness, which leads to low time-efficiency. In this dissertation, we explored new deposition method for C uS and Bi₂S₃ thin films, and investigated structure, properties and application of the deposited samples. The main contents and innovation of this thesis are as follows:（1） Uniform hexagonal covellite C uS thin films were deposited at room temperature by an in-situ solution chemical reaction using solid copper precursor films as cationic source and ammonium sulfide ethanol solution as anionic reaction medium. Influences of ethanolamine, butanol contents, deposition cycle numbers and annealing treatment on the structure, morphology, optical and photoelectronic properties of CuS thin films were investigated. The results showed that the C uS films had two-dimension oriented, half-sheet shaped growing morphology standing disorderly but vertically to substrates, and the calculated texture coefficient TC（102） verified that the half-sheet shaped crystallites were（102） plane orientation. This in-situ multi-deposition process had an average deposited rate of 9 nm per cycle, self-perfect function to grow smooth, uniform and 2D oriented morphology with increase of dip-cycle numbers. The 40 dip-cycles deposited and annealed C uS thin films at 200°C had a better photoelectrochemical performance with photocurrent density of 14.5mA/cm2 at 1V vs Ag/AgCl electrode.（2） Uniform, smooth and densely packed Bi₂S₃ thin films were prepared at room temperature by an in-situ solution chemical reaction. Influence of deposition cycle numbers and annealing treatme nt on the structure, morphology, optical and photoelectronic properties of Bi₂S₃ thin films were investigated. The results showed annealing promoted crystallization to orthorhombic structure as well as crystal growth from very small particles to short-rod shaped nanocrystals. This in-situ deposition had an average deposited rate of 40 nm per cycle and a self-perfect function to grow smooth with increase of dip-cycle numbers. The 8 dip-cycles Bi₂S₃ films annealed at 300°C had a better photoelectrochemical per formance with photocurrent density of 5.03 mA/cm2 bias 0.5 V vs. Ag/AgCl reference electrode.（3） Bi₂S₃ QDs sensitized mesoscopic TiO₂ films and Bi₂S₃/C uS double QDs co-sensitized mesoscopic TiO₂ films were prepared by the in-situ solution chemical reaction deposition. UV- vis-NIR absorption spectra revealed that the Bi₂S₃ and CuS QDs extended range of photo response of the TiO₂ films to the visible region. And the photo-response of TiO₂ films was greatly improved after modification. The Bi₂S₃/CuS co-sensitized TiO₂ solar cells had a maximum conversion efficiency of 0.293% and short-circuit current density of 5.24mA/cm2 under illumination of 1000 W/m2. These results indicate that the Bi₂S₃ and CuS have potential application in the field of QDSSC.