Synthesis And Optoelectronic Properties Of All-inorganic Lead Halide Perovskite CsPbBr₃ Heterostructures

In recent years,all-inorganic lead halide perovskites CsPbX₃（X=Cl、Br、I）,a new emerging semiconductor class,have attracted considerable attention because of their high quantum efficiency,strong visible-light absorption,long carrier diffusion length and high defect tolerance.All-inorganic lead halide perovskites are promising for the applications in high-performance solar cell devices,photodetectors and LED.Compared with single-phase perovskites,heterostructures based on perovskites can further improve the performances of optical and optoelectronic applications due to the tunable carrier transport and structural stability.Since the quality of semiconductor heterostructures is critical for the applications,it is necessary to develop a simple and efficient method for controllable growth of high-quality heterostructures based on all-inorganic lead halide perovskites.In this paper,we develop a variety of epitaxial approach to grow heterostructures based on CsPbBr ₃ with controllable morphology and high quality,and further study their optical and photoelectric properties.The photodetectors based on these heterostructures pos sess excellent performances.The following research results were obtained in this paper:1.The epitaxy of CsPbBr₃ shell on PbSe wire core was realized to form the core-shell PbSe@CsPbBr₃ wire heterostructure via a chemical vapor deposition method.The study of growth mechanism shows that the Pb-particle catalysts at the tips of the PbSe wires provide the nucleation sites for the rapid growth of CsPbBr ₃cube crystals,which serve as the adatom collector for the following shell growth due to the Gibbs–Thomason effect.This determines the directional growth of the shell along the PbSe wires from the tip to bottom.The photoluminescence spectra and time-resolved photoluminescence reveal that the band edge emission of CsPbBr ₃ in the heterostructures is significantly quenched due to the photogenerated electrons transfer from the shell to the core,resulting in the efficient photogenerated carrier separation in the CsPbBr₃ shell.The photodetector based on this PbSe@CsPbBr ₃ wire heterostructure shows high performances under the illumination of 405 nm light,with the photoresponsivity up to 4.7×10⁴ A/W,which is higher than the photodetector based on the individual CsPbBr₃（4.4×10³ A/W）.Furthermore,the PbSe@CsPbBr₃wire heterostructures exhibit a wavelength-dependent photocurrent polarity under the IR-light illumination.2.High-quality CsPbBr₃/CdS heterostructures with the unique 1D morphology have been obtained through a 2-step physical vapor deposition strategy,in which CsPbBr₃ microcubes were grown on the side wall of the free-standing CdS microwires.Theoretical calculations indicates that CdS/CsPbBr ₃ heterojunctions possess the type-II band alignment,which is independent on different crystal surface combinations between CdS and CsPbBr₃.Owing to the effective separation and transportation of photogenerated carriers at the CsPbBr ₃/CdS heterojunction with type-II band alignment,the photodetector based on a single CsPbBr ₃/CdS 1D heterostructure shows high self-powered performances（R=24.5 m A/W）.3.Mixed-dimensional heterostructures of 1D CsPbBr ₃ nanowires/2D Bi₂O₂Se nanoplates have been achieved by a two-step vapor deposition route.The CsPbBr₃wires are well aligned on the Bi₂O₂Se plates in fourfold symmetry with the specific epitaxial relationships.The photoluminescence mapping and spectra reveal that the emission from CsPbBr₃ is significantly quenched in the heterostructure,which is indicative of the carriers transfer from CsPbBr ₃ to Bi₂O₂Se due to the band bending.Additionally,the light emission from the epitaxial CsPbBr ₃ wires can be efficiently absorbed by the Bi₂O₂Se,with the assistance of high-quality waveguide cavity of CsPbBr₃ wires.The photocurrent mapping and spectra of the device based on this mixed-dimensional heterostructure demonstrate that the formation of CsPbBr₃/Bi₂O₂Se heterostructures may significantly improve the optoelectronic response of Bi₂O₂Se.4.The growth of CsPbBr₃ microwires on mica with the physical vapor deposition was in situ monitored by a home-built growth monitoring system based on optical microscope.The evolution of the wires with several tens micron length from nucleuses was observed with the same growth rate in the two opposite axial directions.The wire growth rate strongly depends on theΔT that is defined as the temperature difference between the source and the depositing substrate.This in-situ monitoring of the growth process after the mica reached the thermal equilibrium clearly reveals that the thinner wires have the faster growth rate than the thicker ones,which is consistent with the theoretical analysis based on the adatom diffusion.Besides,the obtained CsPbBr₃ microwires exhibits high-performance photodetections.