Metal halide perovskite materials are an emerging class of solution-processable semiconductors with considerable potential for use in optoelectronic devices1,2,3. For example, light-emitting diodes (LEDs) based on these materials could see application in flat-panel displays and solid-state lighting, owing to their potential to be made at low cost via facile solution processing, and could provide tunable colours and narrow emission line widths at high photoluminescence quantum yields4,5,6,7,8. However, the highest reported external quantum efficiencies of green- and red-light-emitting perovskite LEDs are around 14 per cent7,9 and 12 per cent8, respectively—still well behind the performance of organic LEDs10,11,12 and inorganic quantum dot LEDs13. Here we describe visible-light-emitting perovskite LEDs that surpass the quantum efficiency milestone of 20 per cent. This achievement stems from a new strategy for managing the compositional distribution in the device—an approach that simultaneously provides high luminescence and balanced charge injection. Specifically, we mixed a presynthesized CsPbBr3 perovskite with a MABr additive (where MA is CH3NH3), the differing solubilities of which yield sequential crystallization into a CsPbBr3/MABr quasi-core/shell structure. The MABr shell passivates the nonradiative defects that would otherwise be present in CsPbBr3 crystals, boosting the photoluminescence quantum efficiency, while the MABr capping layer enables balanced charge injection. The resulting 20.3 per cent external quantum efficiency represents a substantial step towards the practical application of perovskite LEDs in lighting and display.
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The data that support the findings of this study are available from the corresponding author upon reasonable request.
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This work was supported by the Scientific Research Funds of Huaqiao University (600005-Z16J0038) and the National Natural Science Foundation of China (U1705256). Z.W. thanks Y. Wang (Technical Institute of Physics and Chemistry, Chinese Academy of Sciences) and J. Wang (Institute of Advanced Materials, Nanjing Tech University) for helpful discussions on how to accurately measure the performance of perovskite LED devices. Z.W. also thanks S. Yang (Hong Kong University of Science and Technology) for carrying out time-of-flight/secondary ion mass spectrometry (TOF-SIMS) analysis. Q.X. acknowledges support from the Singapore National Research Foundation through an NRF Investigatorship award (NRF-NRFI2015-03); and from the Ministry of Education via an AcRF Tier2 grant (MOE-2015-T2-1-047) and Tier1 grants (RG 113/16 and RG 194/17). This publication is based in part on work supported by the Canada Research Chairs program, the Natural Sciences and Engineering Research Council of Canada, and the US Department of the Navy, Office of Naval Research (grant N00014-17-1-2524).
The authors declare no competing interests.
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Extended data figures and tables
a, Photoluminescence spectra of single-layered CsPbBr3, bilayered CsPbBr3/MABr, and quasi-core/shell-structured mixture-1.0 films. b, Photoluminescence spectra of various mixture perovskite films with different amounts of MABr. The numbers in the key indicate the molar ratio of MABr to CsPbBr3. c, Photograph of mixture perovskite films under ultraviolet light. d, The formation process of the CsPbBr3/MABr quasi-core/shell structure. The yellow areas in the left panel denote the precursor solution.
a, Cross-sectional SEM images of the as-prepared mixture-1.0 film at different magnifications. b, Cross-sectional TEM images (greyscale) and elemental mapping images (in colour) of the mixture-1.0 film. The sample was prepared using a focused ion beam, and the top C and Pt layers were predeposited to protect the perovskite film.
a, Estimation of trap-state density using the space-charge-limited current method, obtained using dark I–V curves of perovskite devices with the structure ITO/perovskite/Au. VTFL, trap-filled limiting voltage. b, Photographs of a pristine mixture-1.0 perovskite film (left) and a film treated by washing with IPA (right; to remove the MABr capping layer) under ultraviolet light. c, Photograph of the three perovskite films under ultraviolet light. d, Ultraviolet–visible absorbance spectra of the CsPbBr3 film and different mixture films. The black arrows indicate the disappearance of the exciton peak from the CsPbBr3 sample to the mixture-1.0 sample. e, f, Photoluminescence spectra (e) and time-resolved photoluminescence decay curves (f; excitation source: 400 nm, 4 μW) of the CsPbBr3, MAPbBr3 and mixture-1.0 films. τ is the lifetime.
a, Original and magnified XRD patterns from CsPbBr3, MAPbBr3, mixture-1.0, and MABr + PbBr2 + CsBr mixture perovskite films. 2-theta is the diffraction angle multiplied by 2. b, c, XPS results from CsPbBr3, MAPbBr3 and mixture-1.0 perovskite films, indicating that there are CsPbBr3 and MABr phases in the mixture-1.0 film, but not in MAPbBr3.
Left, top-view SEM image; centre, AFM topography; and right, root-mean-square roughness (R) of the a, CsPbBr3, b, MAPbBr3 and c, mixture-1.0 perovskite films.
a, Energy-level diagram of the as-fabricated perovskite LED. b, Photograph of a large-area perovskite LED device (6 mm × 20 mm). c, Device performance of the bilayered CsPbBr3/MABr perovskite LEDs. S1 and S2 are step 1 and step 2. d, e, Electroluminescence spectra (d) and CIE chromatic diagram (e) of the three as-fabricated perovskite LEDs. f, g, J–V (f) and L–V (g) curves of the three as-fabricated three perovskite LEDs. h, L–V and J–V curves of the best-performing mixture-1.0 perovskite LED without a PMMA layer.
a, Cross-sectional SEM image of a perovskite LED device with a PMMA blocking layer. b, c, AFM topography image (b) and thickness measurement (c) of the optimized PMMA layer. The differently coloured lines show multiple test results from the same sample. d, e, Optimizing device performance by tuning the thickness of the PMMA layer (d) and the amount of MABr additives in the perovskite precursor (e).
Extended Data Fig. 8 Electroluminescence spectra and power efficiency of the best-performing mixture-1.0 perovskite LED device.
a, Electroluminescence spectra at various applied voltages. b, Power efficiency curve.
a, Extrapolation of lifetime from accelerated ageing tests, from which one can see that the acceleration factor, n, is about 1.5 in the devices investigated herein. b, Measurement of the operational lifetime of a perovskite LED working in continuous luminance mode; by carefully tuning the applied current, we could maintain a luminance output of around 100 cd m−2.
Preparing a highly luminous film using the mixture-1.0 precursor.
Real-time measurement of a perovskite LED device.
Measurement of a high-performance perovskite LED device with a current efficiency of 74.2 cd A−1.
Operational lifetime measurement of a perovskite LED device working in continuous mode with luminance of around 100 cd m−2.
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Lin, K., Xing, J., Quan, L.N. et al. Perovskite light-emitting diodes with external quantum efficiency exceeding 20 per cent. Nature 562, 245–248 (2018). https://doi.org/10.1038/s41586-018-0575-3
- External Quantum Efficiency (EQE)
- Balanced Charge Injection
- Perovskite Films
- Perovskite Precursor
- Photoluminescence Quantum Yield (PLQY)
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