Ce3+ doped modulation CsPbBr3 nanocrystal photoluminescence kinetics enhances the performance of perovskite light-emitting diodes

Lead halide perovskite nanocrystals (NCs) are considered to be the next generation of luminescent layer materials for light emitting diodes ( LEDs ). As a typical all-inorganic lead-lead perovskite nanocrystal, CsPbBr3 nanocrystals have high thermal stability, low humidity sensitivity, high color purity and small compared with organic-inorganic hybrid lead halide perovskite nanocrystals. The effective radiation recombination caused by the size exciton constraint has received extensive attention. At present, the composition and band gap regulation of CsPbBr3 nanocrystals can be achieved by rapid anion exchange after synthesis, while retaining the size and morphology of the nanocrystals themselves. Therefore, the diverse synthesis techniques of CsPbBr3 nanocrystals greatly promote their wide application.

Summary of results

Recently, Yao Hongbin (communication author), Zhang Qun (communication author) and the research team of Zeng Haibo (co-author) of Nanjing University of Science and Technology from the University of Science and Technology of China jointly published in J. Am. Chem. Soc. Ce3+-Doping to Modulate Photoluminescence Kinetics for Efficient CsPbBr3 Nanocrystals ba sed Light-Emitting Diodes paper, reported the study of the light/electroluminescence efficiency of CsPbBr3 nanocrystals by doping Ce3+ ions by simple thermal implantation. Since the ionic radius of the Ce3+ ion is similar to that of the Pb2+ ion, and the conduction band level formed by the superposition of the bromide ion orbital is higher than the intrinsic energy level of the CsPbBr3, the Ce3+ ion can be doped into the CsPbBr3 nanocrystal and maintain the calcium. The integrity of the titanium ore structure does not introduce additional trap states. Based on this, they found that by increasing the doping amount of Ce3+ in CsPbBr3 nanocrystals to 2.88%, the photoluminescence quantum yield (PLQY) of CsPbBr3 nanocrystals reached 89%, ultra-fast transient absorption (fs-TA) and Time-resolved photoluminescence (PL) spectroscopy shows that Ce3+ doping can effectively modulate the luminescence kinetics of CsPbBr3 nanocrystals, thereby increasing the PLQY of nanocrystals. At the same time, the external quantum efficiency (EQE) of the device was increased from 1.6% to 4.4% compared with the undoped CsPbBr3 nanocrystals using the CsPbBr3 nanocrystal doped with Ce3+ as the light-emitting layer.

Graphic guide

Figure 1: Micromorphology and spectrogram of Ce3+ doped and undoped CsPbBr3 nanocrystals

Ab: TEM image of Ce3+ doped and undoped CsPbBr3 nanocrystals and corresponding HRTEM images shown in the inset.

c: HAADF-STEM image of Ce3+ doped CsPbBr3 nanocrystals.

Dg: Elemental distribution images of Cs, Pb, Br and Ce in Ce3+ doped CsPbBr3 nanocrystals.

h: PXRD spectra of Ce3+ doped and undoped CsPbBr3 nanocrystals, the inset shows the corresponding crystal structure model.

i: UV-vis absorption and PL spectra of doped and undoped CsPbBr3 nanocrystals, the inset shows a photograph of the corresponding nanocrystal dispersion in toluene under ultraviolet light (365 nm).

Figure 2: Structure and Spectral Characterization of CsPbBr3 Nanocrystals with Different Doping Ce3+ Contents

a: PXRD pattern of Ce3+ doped CsPbBr3 nanocrystals with different CeBr3 precursor concentrations, the inset shows photographs of corresponding colloidal dispersion samples under visible and ultraviolet (365 nm) illumination;

b: left panel: graph of Ce/Pb ratio versus CeBr3 precursor concentration; right panel: UV-visible absorption spectra of doped and undoped CsPbBr3 nanocrystals with different Ce/Pb ratios;

c: Left panel: PL spectra with different Ce/Pb ratios of doped and undoped CsPbBr3 nanocrystals (excited at 365 nm), right panel: plot of PLQY versus CeBr3 precursor concentrations.

Figure 3: Interpretation of the mechanism of the modulated PL dynamics

a: fs-TA spectrum of CsPbBr3 nanocrystals without undoped Ce3+ (left) and its attenuation correlation spectrum analysis (right);

b: fs-TA spectrum of CsPbBr3 nanocrystals doped with Ce3+ (left) and its attenuation correlation spectrum analysis (right);

c: Schematic diagram of the photophysical processes and mechanisms involved, where VB, CB, X1 and Xn represent the valence band, the conduction band, the lowest exciton state and the higher exciton state, respectively, TS represents the band gap trap state, and the asterisk Then indicating a state caused by Ce3+ doping near the CB band edge;

d: The average life of the PL is compared with the trend of the PLQY result (the abscissa is the doping concentration given by the CeBr3 ratio).

Figure 4: LED structure and performance based on Ce3 + doped CsPbBr3 nanocrystals

a: device structure of the LED;

c: EL spectrum at a voltage of 5 V applied and the corresponding PL emission spectra of undoped CsPbBr3 nanocrystals and Ce3+ doped CsPbBr3 nanocrystals dispersed in a toluene solution, the inset shows the corresponding device at an applied voltage of 5 V photo;

d: LED brightness versus drive voltage characteristics based on undoped CsPbBr3 nanocrystals and Ce3+ doped CsPbBr3 nanocrystals;

e: the relationship between the current efficiency of the LED device and the current density;

f: The relationship between the EQE of the LED device and the drive voltage (V).

summary

The team by doping the heterogeneous Ce3+ ions into the colloidal CsPbBr3 nanocrystals by thermal injection to modulate the luminescence kinetics of the nanocrystals and enhance the PLQY, and achieve the preparation of high-efficiency LEDs. The mechanism of the PL enhancement effect is elucidated by ultrafast transient absorption (fs-TA) and time resolved PL spectroscopy. Their LED devices using CsPbBr3 nanocrystals as the luminescent layer increased the external quantum efficiency from 1.6% to 4.4% with the help of Ce3+ doping. Their research shows that the doping of lanthanide ions into perovskite nanocrystals can further diversify the properties of these new semiconductor nanocrystals.

Yao Jisong, a second-year master student at the University of Science and Technology of China, Ge Jing, a postdoctoral fellow, and Han Boning, a second-year doctoral student at Nanjing University of Science and Technology, are the co-first authors of the paper.