Research On Optical Properties And Light Emitting Devices Of All Inorganic Perovskite Quantum Dots

In recent years,all-inorganic lead halide perovskite quantum dots CsPbX₃(X=Cl,Br,I)PQDs have been used in solar cells,light-emitting diodes and light-emitting diodes due to their simple preparation method,large absorption cross-section,high fluorescence quantum efficiency(PLQY),narrow emission line,and tunable fluorescence emission wavelength.Laser and other optoelectronic devices have shown great application prospects.However,despite the vigorous development of research on perovskite quantum dots in recent years,there are still some problems in this material that need to be solved urgently.First of all,due to the ionic characteristics of lead halide perovskite materials,there is a serious anion exchange reaction between different halogen components,so it is difficult to achieve white light emission in this material.Secondly,the quantum efficiency of the blue-violet CsPbCl₃PQDs and CsPb(Cl/Br)₃PQDs is still very low compared to the green and red light with PLQY higher than 90%.In addition,although this kind of lead halide PQDs is expected to become a new generation of display application materials,up to now,the EQE of PQD-LEDs is far lower than that of OLED and?-?QD-LEDs.How to improve the performance of PQD-LEDs is also a problem.Finally,due to the presence of toxic lead elements,the application of lead halide perovskite quantum dots has also been greatly restricted.Therefore,in response to the above problems,this article focuses on how to achieve white light emission and improve the stability of PQDs and how to enhance the luminous efficiency and EQE of PQD-LEDs.The specific work content is as follows:(1)In this work,Bi³⁺/Mn²⁺ions codoped CsPbCl₃PQDs were prepared through the hot injection method for the first time to the best of our knowledge.Through simply adjusting the doping ion concentrations,the co-doped PQDs exhibited tunable emissions spanning the wide range of correlated color temperature(CCT)from19000K to 4250 K under UV excitation.This interesting spectroscopic behavior benefits from efficient energy transfer from the PQDs host to the intrinsic energy levels of Bi³⁺or Mn²⁺codoping ions.Finally,taking advantage of the cooperation between the excitonic transition of the CsPbCl₃PQD host and the intrinsic emissions from Bi³⁺and Mn²⁺ions,white light emission with the Commission Internationale de l'Eclairage(CIE)color coordinates of(0.33,0.29)was developed in the co-doped CsPbCl₃PQDs.(2)In this work,efficient blue-light emitting CsPbBr₃PQDs with PLQY of 72%were developed through a bandgap engineering approach.The achieved blue-light emitting PLQY was much higher than the values acquired in the inorganic PQDs in the literature.And the emission color of the as-prepared PQDs can be facially tuned by only adjusting the reaction temperature.Further,the mono-dispersed PQDs@SiO₂composites were constructed benefiting from the low temperature synthesis.The optical performance of the PQDs could be well persisted even in the moisture environment.Finally,the as-prepared PQDs@SiO₂composite was fabricated as the PQD ink on the anti-counterfeit printing technology,from which the obtained pattern would emit varied color under UV lamp.And the as-prepared composites were also applied for fabricating WLED,with Commission Internationale de l'Eclairage(CIE)color coordinates of(0.33,0.38)and power efficiency of 32.5 lm W^-1,demonstrating their promising potentials in solid-state lighting.(3)The lead-free 0D K₃SbCl₆perovskite nanocrystals(PNCs)were firstly developed by the hot injection synthesis method.Through controlling the synthetic temperature,the as-prepared NCs exhibit the blue emission centered at 440 nm with the highest PLQY of 22.3%.Furthermore,the Mn²⁺ions were further doped into 0D lead-free K₃SbCl₆PNCs,leading to the additional red-light emission attributed to the intrinsic transition(⁴T₁-⁶A₁)of Mn²⁺ions.By controlling the Mn²⁺ion doping concentration,the white light emission with PLQY of 37.2%was realized.Finally,the WLEDs with the Commission Internationale de L'Eclairage 1931(CIE)of(0.29,0.28),(0.32,0.30)and(0.35,0.30)were fabricated by combining the as-prepared Mn²⁺-K₃SbCl₆PNCs with commercial 365 nm UV light chips.The performances of the as-fabricated WLEDs were modulated with tunable correlated color temperature(CCT)from 8173to 4779 K,which exhibit the high color-rendering index(CRI)more than 80.These results provide the opportunity for the future applications of 0D lead-free PNCs in the lighting and lasing field of LEDs.(4)We fabricated the high performing blue-light emitting PQD-LED based on the phenethylammonium chloridesynonym(PEACl)modified CsPb(Cl/Br)₃PQDs.Firstly,the PEA-CsPbCl₃PQDs were synthesized by introducing the certain amounts of PEACl in the conventional hot-injection synthesis process.The merit of our synthesis lies in the fact that not only the Cl vacancies of CsPbCl₃PQDs are efficiently modified by introducing the PEACl precursor,but also the partial long-chain organic ligands(OLA)capping on the surface of CsPbCl₃PQDs are simultaneously replaced by the shorter PEACl chains.Consequently,the PEA-CsPbCl₃PQDs emitted at 410nm with the PLQY of 62.3%was achieved.Furthermore,to meet the requirement of display application,we exchange Cl-with Br-ions at room temperature to precisely control the blue emission in 460-470 nm spectral regions and with the maximum PLQY of 80.2%at 470 nm.Finally,the PQD-LEDs based on PEA-CsPb(Cl/Br)₃PQDs emitted at 462,465,468 and 470 nm were fabricated.The PQD-LEDs exhibit the maximal EQE of 2.15%and luminance of 620 cd/m²,which provides a highest value of luminance for the PQD-LEDs in the blue spectral range that satisfying the practical display applications.(5)We reported a strategy to improve the performances of PQD-LEDs by utilizing the localized surface plasmon resonance(LSPR)effects of Au nanospheres(NSs).It was accomplished by introducing Au NS layer into the electron transport layer of Ca²⁺-CsPbBr₃PQD-LED,where the diameter and spacing of Au NSs as well as the interaction distance between the Ca²⁺-CsPbBr₃PQD and Au NS layers have been precisely modulated,according to our preliminarily theoretical simulation of Finite-difference time-domain(FDTD).In addition,the photoluminescence(PL)performance of CsPbBr₃PQD emitting layer was also enhanced by the passivation of calcium ions.Based on the above cooperative effects,the PLQY of Ca²⁺-CsPbBr₃PQD layer emitted at 515 nm has been significantly improved from 31.5%to 73.3%.Moreover,the carrier transportation process of the PQD-LEDs was also investigated by introducing Au NS layer into the electron transport layer,which demonstrated that the carrier injection balance of the device is improved.As a result,the luminance of green emitting PQD-LEDs was improved from 16824 to 63931 cd/m²and EQE is improved from 4.2%to 10.5%.