Preparation Of Copper Zinc Tin Sulfur Suitable For Sensitized Solar Cell Electrode Materials

The copper-zinc-tin-sulfur(Cu₂ZnSnS₄,CZTS)quaternary semiconductor material is rich in constituent elements,safe and non-toxic,its band gap energy is close to the optimal band gap energy of solar cell and the light absorption coefficient(>10~4cm^-1)is high,its crystal structure is similar to that of copper indium gallium selenide semiconductor materials,and it has a potential applications in the field of solar cells.In this thesis,CZTS nanocrystalline thin films were prepared on FTO conductive glass by the spin coating,and their performance as a counter electrode for dye-sensitized solar cells was studied,and the preparation conditions were optimized.Further,Co₉S₈was deposited on CZTS thin film to form the composite thin film electrode,the mechanism of improving the catalytic performance of the composite counter electrode was studied.CZTS nanocrystals were grown in situ on TiO₂nanocrystalline thin film by the successive ionic layer adsorption and reaction(SILAR)method,and its application as a quantum dot sensitizer in quantum dots-sensitized solar cells was studied.The main research contents are as follows:(1)CZTS thin films with different spin coating numbers were prepared on FTO conductive glass by spin coating.The phase purity and crystal structure of the films were characterized by X-ray diffraction(XRD)and Raman(Raman)spectroscopy,and the composition of the films was characterized by energy dispersive X-ray spectroscopy(EDS)and X-ray photoelectron spectroscopy(XPS).The performance of CZTS thin films as counter electrodes for dye-sensitized solar cells was evaluated by measuring the cyclic voltammetry,photocurrent density-voltage curves,electrochemical impedance spectroscopy and Tafel polarization curves of the thin film electrodes.The effect of spin coating times on the morphology,thickness and catalytic performance of the films was investigated.The number of spin coats affects the surface morphology and thickness of CZTS films,so the electrocatalytic performance of CZTS films can be tuned by changing the thickness.When the spin coating times was 3,the thickness of CZTS thin film was moderate and the nanoparticles were tightly bound,and the electrocatalytic performance of the CZTS film is the best.(2)A metal-organic framework ZIF-67 was deposited on the CZTS film prepared by spin coating by electrophoretic deposition,and further sulfided to convert ZIF-67into Co₉S₈to form a composite thin film of CZTS and Co₉S₈.By measuring the cyclic voltage curve,photocurrent density-voltage curve,electrochemical impedance spectroscopy and Tafel polarization curve of the composite film electrode,the effect of Co₉S₈composite on the catalytic activity of CZTS thin film was evaluated.The highest photoelectric conversion efficiency of the dye-sensitized solar cell based on the optimized composite thin film counter electrode reached 6.41%.The high photoelectric conversion efficiency is attributed to the good interfacial transfer of photogenerated electrons and the redox reversibility of the electrolyte on the as-prepared composite electrodes.(3)CZTS nanoparticles were prepared on the surface of TiO₂nanocrystalline thin films by the SILAR method.The effect of the number of SILAR cycle on the structure and morphology of CZTS nanoparticles was studied by XRD,Raman,XPS,EDS,etc.When the SILAR process was repeated for 5 times,the grain size of the CZTS nanoparticles was relatively uniform,and the nanoparticles were uniformly covered on the surface of TiO₂nanocrystalline thin film.The prepared CZTS quantum dots sensitized TiO₂nanocrystalline thin film was used as the photoanode,and the Co₉S₈/FTO electrode was used as the counter electrode to form a"sandwich"structure quantum dots-sensitized solar cell.The photocurrent density-voltage curve and electrochemical impedance spectroscopy test show that the photoelectric conversion efficiency of the solar cell assembled by CZTS quantum dots is the highest when the SILAR cycle number is optimized as 5.