Preparation And Performance Of CZTS Thin Film Solar Cells

Copper-zinc-tin-sulphur?CZTS?film is suitable to be the absorb materials of thin-film solar cells due to the rich content of Cu,Zn,Sn,S on earth,non-toxic,the band gap of 1.4–1.5 e V and large absorption coefficient over 10⁴ cm^-1.In this paper,we had fabricated single phase CZTS films on the FTO conductive glass substrate using electrodeposition method.Copper sulfate,zinc sulfate,stannous sulfate and sodium thiosulfate were main salt,as a source of Cu,Zn,Sn,S elements,and sodium citrate acted as complexing.We studied the influence of factors including the concentration of each compound,the temperature of heat treatment,deposition potential and p H conditions on the properties of CZTS films cell by single factor experiment,and achieved the optimum film.Optimum conditions are that Cu SO₄ concentration of 0.010 mol/L,Zn SO₄ concentration of 0.050 mol/L,Sn SO₄ concentration of 0.050mol/L,sodium thiosulfate concentration of 0.50 mol/L,sodium citrate concentration of 0.20 mol/L,p H value of 4.00,the deposition potential of 1.4 V,the deposition time of 15 min,the heat treatment temperature of 500?.Using cyclic voltammetry tested on electrochemical workstation,cyclic voltammetry curves of Cu,Zn,Sn,S,and four mixing elements were obtained,and the mechanism of CZTS film were also indicated according to the graph of oxidation-reduction peak.CZTS thin film semiconductor material acts as the battery-absorbing layer.If we wanted to get the fully battery system,we must choose a suitable semiconductor material which act as battery buffer layer.In the paper,we chose a cheap and non-toxic semiconductor material,that is Zn S,as buffer battery layer,and the Zn S thin films were prepared using electrodeposition method successfully.Finally,we made up of a solar cell with CZTS film and Zn S film and then tested it using the electrochemical workstation.The values of V_oc,I_scc were obtained and the efficiency of cell was calculated.The band gap of the film was measured by UV-visible spectrophotometer;photoelectric performance of films were tested using linear scanning;the composition and structure of the films were characterized through X-ray diffraction;the surface structure of the films were analyzed using a scanning electron microscope?SEM?and atomic force microscopy?AFM?;X-ray photoelectron spectroscopy?XPS?was used to characterize the chemical state of the film.Results revealed that the band gap of CZTS films was 1.5 e V after heat treatment and the photoelectric curve shifted yield to be 35.23%.The surface presented more uniform and dense.The crystallinity was improved due to the existence of CZTS crystalline phase.The cell efficiency was 1.5565×10^-2%under the optimal conditions.The surface structure of the film had changed after heat treatment and the crystallinity was improved,EDS and XRD analysis demonstrated that there exist Zn and Zn O miscellaneous except ZnS.