| Lead chalcogenide quantum dots are direct bandgap semiconductor materials and they have been extensively investigated due to excellent properties of high fluorescence quantum yields,large exciton Bohr radius,wide wavelength tuning range and efficient multi-exciton emission.However,it is still difficult to extend the lead chalcogenide quantum dots from wet chemical synthesis to the application of high-performance optoelectronic devices.This is because the surface atomic activity of the lead chalcogenide quantum dots is high,which is easy to be oxidized and doped,resulting in uncontrollable changes in the photoelectric properties of quantum dots.On the other hand,the dangling bond defects and long chain ligands on the surface of lead chalcogenide quantum dots lead to the difficulty of carrier transport,which will prompt the poor performance of optoelectronic devices.Therefore,PbS and PbSe quantum dots are synthesized in this paper.The problems of poor luminescent stability and carrier transport are improved through core-shell structure and TBAI ligand.The specific contents and related results are as follows:(1)By adjusting the growth time of quantum dots,PbS quantum dots with peaks located at 1330 nm,1420 nm and 1500 nm were synthesized.The results of transmission electron microscopy(TEM),X-ray diffraction(XRD),infrared absorption(Abs),and photoluminescence spectroscopy(PL)showed that the quality of the synthesized quantum dots was good.The thermal activation process of carriers in PbS quantum dots with emission peaks located at 1330 nm and 1420 nm was observed through the temperature-and power-dependent PL spectra.In order to improve the stability of PbS quantum dots,PbS/CdS quantum dots with different shell thicknesses were synthesized by cation exchange,which greatly improved the luminescent stability of PbS quantum dots.But the CdS shell structure also reduced the luminescent intensity of quantum dots,which is due to the introduction of new defect states in PbS quantum dot.Finally,the influence of TBAI ligand on the photoelectric properties of quantum dots is studied.The photodetector fabricated with PbS-TBAI quantum dots has the fastest response speed,reaching 1.45 seconds,which is 81 % higher than that of quantum dots without ligand exchange.(2)A series of PbSe quantum dots with different PL peaks position were synthesized.And the peaks for PbSe quantum dots located at 1767 nm,1975 nm and2004 nm were measured by temperature-and power-dependent PL spectra.The results showed that quantum dots with peaks located at 1767 nm were exposed to air for a period of time,and the luminescent intensity decreased with the increase of temperature.The intensity of the PL for unoxidized quantum dots of peaks located at1975 nm and 2004 nm increased with the increase of temperature.PbSe/CdSe quantum dots structure was used to improve the luminescent stability of the PbSe core quantum dots.The CdSe shell passivated the original defects on the surface of PbSe quantum dots,making its PL spectrum change from a shape with a long tail at the high energy end to a symmetric Gaussian waveform,but the new defects caused the decrease of the luminescent intensity.PbSe,PbSe/CdSe quantum dots were applied to fabricated photodetectors,and TBAI ligand was used to reduce the spacing of quantum dots.PbSe/CdSe-TBAI quantum dot photodetectors have the fastest response speed,this is because CdSe may improve the trap-state of quantum dots due to oxidation.In this paper,the synthesis of lead chalcogenide quantum dots and the fabrication of optoelectronic devices have been realized.The dynamics of carriers have been studied by temperature-and power-dependent PL spectra.The core-shell structures synthesized by cation exchange have greatly improved the luminescent stability of quantum dots.TBAI ligand has reduced the spacing of quantum dots and improved the transmission of carriers.This paper laid the foundation for the realization of high-performance infrared optoelectronic devices. |
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