| CuZnSn(S,Se)4(CZTSSe)is a direct band gap p-type semiconductor material,which has good optoelectronic properties,absorption coefficient of as high as 10~4 cm-1,and the band gap of 1.0?1.5 eV that is close to the ideal band gap for solar cells absorpber.In addition,the elements in CZTSSe are safe and non-toxic and abundant in the earth's crust and are.Using flexible metal Mo foil as the substrate for CZTSSe has the advantages of low cost,ductility and thermal expansion coefficient compatible with CZTSSe thin films.Because a large number of Se atoms pass through the CZTSSe thin film during the high temperature selenization,the Mo(S,Se)2 interface layer is easily formed between CZTSSe layer and Mo foil,which hinders the movement of electrons to Mo foil,affecting the photoelectric conversion efficiency of solar cells.Therefore,it is necessary to decrease the thickness of the Mo(S,Se)2 interfacial layer through interfacial regulation to further optimize the CZTSSe/Mo interface contact properties.In this thesis,the CZTSSe thin films were prepared on flexible metal Mo foil and Mo-coated glass substrates by sol-gel method and post-selenization method.The influence of substrate on the formation of Mo(S,Se)2 interface layer is investigated.The reasons for the formation of interface layer are analyzed.Then,the thickness of the Mo(S,Se)2 interface layer is modulated by pre-annealing the metal Mo foil substrate,chemically polishing the substrate,adding a CuCrO2 or Mo buffer layer between the CZTSSe and Mo foil.The research works are summarized as follows:(1)The influence of substrate on the contact properties of CZTSSe thin films and CZTSSe/Mo interface is investigated.At the same selenization temperature,the grains of the CZTSSe thin film on the Mo foil substrate are larger than that on the Mo-coated glass substrate.With the increase of selenization temperature,there is a thick Mo(S,Se)2 interface layer between CZTSSe and Mo foil substrate.However,the interface layer cann't be found between CZTSSe and Mo-coated glass substrate.When the selenization temperature is550°C,the surface particles of the CZTSSe thin film on the Mo foil substrate are uniform,the thin film is flat and dense,and the resistance of CZTSSe/Mo(S,Se)2/Mo decreases to10.5?.(2)The contact properties of CZTSSe/Mo interface are regulated by pre-annealing of metal Mo foil substrate.The pre-annealing of Mo foil substrate can weaken the intensity of Mo(S,Se)2 diffraction peak and decreases the thickness of Mo(S,Se)2 interface layer to 0.85?m.The slope of the I-V curve of CZTSSe/Mo(S,Se)2/Mo structure increases to 0.18 S.(3)The effect of chemical polishing of metal Mo foil substrate on the properties of CZTSSe thin films and CZTSSe/Mo interface is investigated.The thickness of the Mo(S,Se)2 interface layer decreases by Mo foil substrate polishing.When the Mo foil substrate is polished with acidic H2O2 solution,the thickness of the Mo(S,Se)2 interface layer decreases to 5.01?m.The ohmic contact between CZTSSe thin film and Mo foil substrate is the best.The slope of the I-V curve of CZTSSe/Mo(S,Se)2/Mo increases to 0.233 S.(4)The effect of CuCrO2 buffer layer on the properties of CZTSSe thin films and CZTSSe/Mo interface is investigated.With the increase of the thickness of CuCrO2 buffer layer,the intensity of Mo(S,Se)2 diffraction peak weakens,the thickness of Mo(S,Se)2interface layer decreases,and the slope of I-V curve of CZTSSe/Mo structure increases.When the thickness of the CuCrO2 layer increases to 113 nm,Mo(S,Se)2 interface layer can not be found between CZTSSe thin film and Mo foil substrate by SEM,and the resistance of the CZTSSe/Mo structure reaches a minimum value of 1.1?.(5)The interface contact properties of CZTSSe/Mo are regulated by adding a Mo buffer layer between the CZTSSe thin film and the Mo foil substrate.Mo buffer layer can effectively decrease the thickness of the Mo(S,Se)2 interface layer.When the thickness of Mo buffer layer increases to 242 nm,as detected by SEM and EDS,the layer between the CZTSSe thin film and the Mo foil substrate is Mo instead of,Mo(S,Se)2.The slope of the I-V curve of the CZTSSe/Mo structure reaches a maximum value of 0.691 S.In summary,within the scope of this study,adding a CuCrO2 buffer layer between CZTSSe and Mo foil substrate is the best way to regulating the Mo(S,Se)2 interface layer.When the thickness of CuCrO2 buffer layer increases to 113 nm,Mo(S,Se)2 interface layer can not be detected between CZTSSe and Mo foil substrate,which can enhance the interface contact characteristics between CZTSSe and Mo foil substrate.The slope of I-V curve increases to 0.973 S,and the resistance of the CZTSSe/Mo structure decreases to 1.1?. |
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