Abstract
Light-emitting diodes (LEDs) based on perovskite quantum dots (QDs) have produced external quantum efficiencies (EQEs) of more than 25% with narrowband emission1,2, but these LEDs have limited operating lifetimes. We posit that poor long-range ordering in perovskite QD films—variations in dot size, surface ligand density and dot-to-dot stacking—inhibits carrier injection, resulting in inferior operating stability because of the large bias required to produce emission in these LEDs. Here we report a chemical treatment to improve the long-range order of perovskite QD films: the diffraction intensity from the repeating QD units increases three-fold compared with that of controls. We achieve this using a synergistic dual-ligand approach: an iodide-rich agent (aniline hydroiodide) for anion exchange and a chemically reactive agent (bromotrimethylsilane) that produces a strong acid that in situ dissolves smaller QDs to regulate size and more effectively removes less conductive ligands to enable compact, uniform and defect-free films. These films exhibit high conductivity (4 × 10−4 S m−1), which is 2.5-fold higher than that of the control, and represents the highest conductivity recorded so far among perovskite QDs. The high conductivity ensures efficient charge transportation, enabling red perovskite QD-LEDs that generate a luminance of 1,000 cd m−2 at a record-low voltage of 2.8 V. The EQE at this luminance is more than 20%. Furthermore, the stability of the operating device is 100 times better than previous red perovskite LEDs at EQEs of more than 20%.
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Data availability
The data that support the findings of this study are available from the corresponding author upon request.
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Acknowledgements
We acknowledge the financial support from the National Natural Science Foundation of China (NSFC) (62205230 and 62175171), the Suzhou Key Laboratory of Functional Nano and Soft Materials, the Collaborative Innovation Center of Suzhou Nano Science and Technology (CIC-Nano), the 111 Project and the Joint International Research Laboratory of Carbon-Based Functional Materials and Devices. We acknowledge the Sargent group at the University of Toronto for providing access to the experimental facilities. This publication is based, in part, on the work supported by the Natural Sciences and Engineering Research Council of Canada.
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L.-S.L. supervised the project; L.-S.L. and Y.-K.W. conceived the idea and wrote the Article; Y.-K.W. and H.W. prepared the perovskite QDs, fabricated LEDs and performed the characterization of LEDs; S.T. and L.G. performed the GIWAXS and GISAXS measurements; Z.Z. performed the conductivity measurements under the supervision of S.-D.W.; F.Z. and H.-W.D. performed the optical measurements; F.Z., H.-W.D. and M.I. took the TEM measurements and performed the other morphology characterizations; and S.H. contributed to data analyses and provided instructive suggestions. All authors discussed the results and assisted in the preparation of the Article.
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Extended data figures and tables
Extended Data Fig. 1 Property of original sample and thermal stability comparison.
a–c, Photoluminance spectra (a), excitation-dependent PLQY (b) and field-effect transistors (c) of original film. d, The emission peak dependence on aging time Inset: initial PL spectra of the original, control and treated perovskite films, and after 50 min.
Extended Data Fig. 2 In situ PL spectra measurements.
a, Scheme illustrating the system for the in situ PL measurement. It consists of 405 nm LED as a light source, optical fibers, a QE-Pro spectrometer (Ocean Optics) and a laptop. b, In situ time-dependent PL spectra of a QD solution during ligand exchange. The red arrow indicates the time the TMSBr was added. c, Extracted peak positions and FWHM from b.
Extended Data Fig. 3 Analysis of QD composition and arrangement.
a, XPS analysis showing the control and treated films have a similar composition with Br/I ratio difference <5%. b, FTIR results of original, control and treated films. c–d, TEM images of control (c) and treated (d) QDs supporting the claim of long-range order films for the treated CsPbBrxI3−x.
Extended Data Fig. 4 DFT calculation and crystal arrangement analysis.
a, Binding structure of OAc/OAm, AnHI and TMSBr on the surface of the nanocrystals. b, Electrostatic potential distribution in the AnHI and TMSBr molecules. c, Calculated binding affinity energy of AnHI and TMSBr, using OAc/OAm ligands as the control. d, The assigned Brag spots to CsPbBr3 with an extended lattice constant due to Iodine incorporation using GIXSGUI.
Extended Data Fig. 5 QD film stability and thickness analysis of LEDs.
a–c, PL mapping (a), SEM images (b) and AFM images (c) of original, control and treated CsPbBrxI3−x films. d, Cross-sectional TEM images show the thickness of each layer (the elemental distribution of Al, Pb and O as reference). e–f, AFM images with the thickness measurement details of the control films. g–h, AFM images with the thickness measurement details of the treated films.
Extended Data Fig. 6 Device performance of original and control LEDs.
a,b, Current density-voltage, luminance-voltage, EQE versus luminance curves of original (a) and control (b) LEDs.
Extended Data Fig. 7 LED performance emitting in the pure-red region.
a–d, Current density-voltage (a), luminance-voltage (b), EL spectra (c) and EQE versus luminance curve (d) of the pure-red LEDs with EL peak in the range of 630–640 nm. e–f, Quantitative statics and standard deviation for batch-to-batch (e) and performance variation within one batch (f).
Extended Data Fig. 8 Device interface engineering.
a, Device structure using PEDOT:PSS as the HIL and TPBI as the ETL, and the current density-voltage, luminance-voltage, EQE versus luminance curves of the LEDs. b, Device structure using NiOx/SAM as the HIL and TPBI as the ETL, and the current density-voltage, luminance-voltage, EQE versus luminance curves of the LEDs. c, Device structure using PEDOT:PSS as the HIL and CNT2T as the ETL, and the current density-voltage, luminance-voltage, EQE versus luminance curves of the LEDs.
Extended Data Fig. 9 Extracted LED stability.
a, Measured stability at luminance of 1100 cd m−2, 2200 cd m−2, 3150 cd m−2 and 4200 cd m−2. b, Extracted stability from the measured “n” derived from (a). c–f, Input voltage change during the operational lifetime measurements.
Extended Data Fig. 10 Analysis of aged control and treated LEDs.
a,b, TOF-SIMS depth profiles of the control (a) and treated (b) CsPbBrxI3−x LEDs before (a,d) and after electrical stress (continuous electrical aging at 1000 cd m−2 for 30 min) (b,e). c,d, Scheme illustrating the Br/I migration to the adjacent layers in control and the suppressed Br/I ion migration in the treated LEDs. e,f, EL spectra of original and control LEDs held at a current density of 10 mA cm−2 for 30 min. g, EL spectra of treated LEDs held at different current densities.
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Wang, YK., Wan, H., Teale, S. et al. Long-range order enabled stability in quantum dot light-emitting diodes. Nature 629, 586–591 (2024). https://doi.org/10.1038/s41586-024-07363-7
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DOI: https://doi.org/10.1038/s41586-024-07363-7
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