Study On The Preparation And Performance Of Carbon Nanofiber Supported All-inorganic Cesium Lead Halide Perovskite

All-inorganic cesium lead halide perovskite CsPbX₃（X=Cl,Br,I）has attracted the attention of researchers because of its excellent performance,such as good thermal stability,broad bandgap tunability,excellent charge transport properties and so on.As an alternative to organic-inorganic hybrid perovskites,it is widely used in photoelectric devices such as solar cells,photodetectors and light-emitting diodes.The morphology and size of all inorganic perovskite materials have significant effects on the properties.At present,most of the methods for the controlled synthesis of all-inorganic perovskite nanomaterials are based on the hot-injection method.It is generally acknowledged that hot-injection method requires inert gas and the isolation and purification of products are a tough step,so it’s difficult to be used for large-scale synthesis.While maintaining the excellent properties of all-inorganic perovskite materials,improvements in synthetic technology are the focus of current research.In order to improve the synthesis technology of perovskite materials,the composite material of all-inorganic perovskite and carbon nanofibers is prepared by free liquid surface electrospinning.The synergistic effects can be expected by combining the strengths of all-inorganic halide perovskite and carbon nanofibers.The main research work of this thesis are as follows:（1）The carbon nanofiber-loaded CsPbI₃ perovskite material was successfully prepared by free liquid surface electrospinning and following thermal treatment.The effects of perovskite precursor solution concentration,solvent composition,polymer type and thermal treatment conditions on the morphology and structure of the fibers were investigated.It was found that the optimal conditions for preparing CsPbI₃/carbon nanofiber composites were 0.5M perovskite precursor and 7 wt%PAN dissolved in DMF as spinning solution,the obtained CsPbI₃/PAN fibers were pre-oxidized at 250℃ for 1h and then calcined at 400℃ in vacuum for 1h.The preparation method has the advantages of simple operation,flexible shape adjustment and large-scale preparation,providing a new idea for the preparation of all-inorganic perovskite materials.（2）The CsPbl₃ crystals prepared by this method are single-crystalline with good crystallinity,which can be uniformly grown on high-aspect-ratio carbon nanofibers.Moreover,there is a strong bond between the CsPbl₃ crystals and the carbon nanofiber.After thermal treatment,the peak position of XPS shifts toward the high binding energy,indicating the interaction between the carbon nanofibers and the surface of CsPbl₃.Although cubic phase CsPbl₃ is easily transformed to orthorhombic phase under ambient conditions,the composite fibers can maintain the phase stability of the cubic phase CsPbI₃ to some extent.Moreover,the CsPbl₃ crystals grown on carbon nanofibers have good thermal stability and high melting point.In terms of optical properties,the CsPbI₃/PAN composite fiber before thermal treatment showed a wide bandgap of 2.71 eV,while the heat treated CsPbI₃/carbon nanofiber showed stronger absorption and similar absorption peak.（3）The carbon nanofiber-loaded CsPbI₂Br,CsPblBr2 and CsPbBr₃ composites were prepared respectively by electrospinning and following thermal treatment.The characterization results reveal that they have different morphology,crystal structure and optical properties.The composite fiber material obtained by electrospinning has a certain degree of crystallinity,and a phase transition occurs in the perovskite crystal grown on the fiber after thermal treatment.Changing the proportion of halide causes the diffraction peak to shift.The peak position shift to a larger angle with the increase of Br content.In addition,the absorption peak and emission peak of CsPbI₃-xBrx perovskite are blue-shifted with the increase of Br content,and the bandgap is increased.These results demonstrate that materials with different structures and properties can be obtained by halide replacement of perovskite precursor.The fluorescence quenching phenomenon after thermal treatment also indicates that the carbon nanofiber-loaded perovskite material has good electron transfer capability.The photoresponse test of composites shows that CsPbI2 Br perovskite has excellent absorbance and carrier transport properties.The tight bond between CsPbI₂Br crystals and carbon nanofibers also enhances the charge transfer capability at the interface,enabling photocurrent significantly larger than dark current,which is suitable for applications on photodetectors.