Synthesis Of Tungsten/molybdenum Disulfide Quantum Dots And Their Optical-Electronic Devices

Transition metal dichalcogenides?TMDs?with characteristic physicochemical properties have good prospects for applications as sensor,optoelectronic device,energy storage,et al.At the beginning of our research in 2016,the leading synthesis for WS₂ and MoS₂ quantum dots?QDs?basically relied on top-down method,which is pure physical exfoliation.These methods lead to nonuniform size distribution,poor shape-control,difficult purification,and low photoluminescence quantum yield?PLQY?,limiting some applications such as light-emitting devices?LEDs?.To solve these problems,first,from the perspective of synthesis,we designed a simple,time-saving and bottom-up colloidal synthesis method,and synthesized a series of WS₂/MoS₂ QDs with different sizes in a controllable manner.Second,from the perspective of optical properties,in view of the low PLQY and unclear photoluminescent?PL?mechanism,we passivated the surface defects of WS₂ QDs to reduce the number of non-radiation centers and increase PLQY from 6%to 32%.By combining the temperature-dependent PL with absorption characteristics,the exciton recombination process of WS₂ and MoS₂ QDs was studied and a radiation model was proposed.Third,compared to traditional CdS,CdSe and PbS QDs,WS₂ and MoS₂QDs bear good biocompatibility and optical stability,and their broad-band PL is suitable for white LEDs.Meanwhile,WS₂ and MoS₂ are good energy storage materials.WS₂ and MoS₂ QDs with a large number of edge atoms and surface defects have great application prospects in energy storage device.From the perspective of optoelectronic devices,WS₂ and MoS₂ QDs were applied to electro-LED and PL LEDs as luminescent layers.And based on surface effects,WS₂ QDs were applied to supercapacitors as electroactive materials.The supercapacitor's stability can reach8000 charge/discharge cycles.?1?In order to optimize the tedious process of physical synthesis and improve the low quality of QDs,we adopted colloidal synthesis method,and studied the structure,quantum confinement effects and PL properties by combining the experimental characterizations and theoretical calculation.?2?QDs'PLQY is closely affected by the surface composition.As the size of QDs decreases,the surface defects of non-radiative increase,resulting in more PL quenching.In order to solve low PLQY issue,we identified and passivated the surface defects of WS₂ QDs,thereby reducing the number of non-radiative centers and increasing the PLQY to 32%.Besides,we overcame the difficulty in forming good WS₂ QD film.And via solution-processed method,they were applied to the electro-white LED with adjustable color temperature and maximum color rendering index?CRI?of 91.?3?In order to avoid the release of toxic gases from organics during the synthesis,we used highly active inorganic sulfur to synthesize stable and bright WS₂ QDs.The white LEDs with a stable electroluminescence spectra and CRI of 93 were fabricated,using the non-toxic and broad-band PL emission of silver indium sulfide?AgIn₅S₈?QDs to make up the WS₂ QDs'PL in the red region.?4?In order to figure out the PL mechanism of MoS₂ QDs,a reasonable exciton recombination model was proposed to explain the excitation wavelength-dependent PL,according to PL kinetics and PL decay spectrum.Based on re-absorption properties,multicolor LEDs covering the whole visible region were fabricated using single MoS₂ QDs as a luminous material.?5?For WS₂ QDs,as electroactive material of supercapacitors,long chain organic ligands on the particle surface will inhibit their conductivity and contraction between electrolyte with active sites.Based on this,ligand exchange method was applied to replace the original ligands with short-chain and high activity ethanedithiol?EDT?,so as to increase the conductivity,optimize the contact and improve the specific capacitance.To sum up,we optimized the synthesis route of WS₂/MoS₂ QDs,reduced time cost,improved the PLQY and conductivity,and applied them to white LED and capacitors.This work may help the further study and fabrication of WS₂/MoS₂ QD and their optoelectronic devices.