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.