Abstract
Lighting accounts for one-fifth of global electricity consumption1. Single materials with efficient and stable white-light emission are ideal for lighting applications, but photon emission covering the entire visible spectrum is difficult to achieve using a single material. Metal halide perovskites have outstanding emission properties2,3; however, the best-performing materials of this type contain lead and have unsatisfactory stability. Here we report a lead-free double perovskite that exhibits efficient and stable white-light emission via self-trapped excitons that originate from the Jahn–Teller distortion of the AgCl6 octahedron in the excited state. By alloying sodium cations into Cs2AgInCl6, we break the dark transition (the inversion-symmetry-induced parity-forbidden transition) by manipulating the parity of the wavefunction of the self-trapped exciton and reduce the electronic dimensionality of the semiconductor4. This leads to an increase in photoluminescence efficiency by three orders of magnitude compared to pure Cs2AgInCl6. The optimally alloyed Cs2(Ag0.60Na0.40)InCl6 with 0.04 per cent bismuth doping emits warm-white light with 86 ± 5 per cent quantum efficiency and works for over 1,000 hours. We anticipate that these results will stimulate research on single-emitter-based white-light-emitting phosphors and diodes for next-generation lighting and display technologies.
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Data availability
The datasets analysed during the study are available from the corresponding authors upon request.
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Acknowledgements
This work was financially supported by the National Natural Science Foundation of China (51761145048 and 61725401), the National Key R&D Program of China (2016YFB0700702, 2016YFA0204000 and 2016YFB0201204), the HUST Key Innovation Team for Interdisciplinary Promotion (2016JCTD111) and the Program for JLU Science and Technology Innovative Research Team. The calculation of broadband emission at the University of Toledo was supported by the Center for Hybrid Organic Inorganic Semiconductors for Energy (CHOISE), an Energy Frontier Research Center funded by the Office of Basic Energy Sciences, Office of Science within the US Department of Energy. The analysis of the electronic properties of halide double perovskites was funded by the Office of Energy Efficiency and Renewable Energy (EERE), US Department of Energy, under award number DE-EE0006712. Part of the code development was supported by the National Science Foundation under contract number DMR-1807818. Y.Y. acknowledges support from the Ohio Research Scholar Program. For the theoretical calculations we used the resources of the National Energy Research Scientific Computing Center, which is supported by the Office of Science of the US Department of Energy under contract number DE-AC02-05CH11231. Y.G. and J.E. acknowledge financial support by the Australian Research Council (DP150104483) and the use of instrumentation at the Monash Centre for Electron Microscopy. The authors from HUST thank the Analytical and Testing Center of HUST and the facility support of the Center for Nanoscale Characterization and Devices, WNLO. We also thank Z. Xiao for useful discussion about emission mechanisms and some XRD measurements, as well as T. Zhai, H. Song, Y. Zhou, H. Han, X. Lu and L. Xu for providing access to some facilities.
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Nature thanks C. C. Stoumpos and the other anonymous reviewer(s) for their contribution to the peer review of this work.
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J.T. conceived the idea and guided the whole project. J. Luo, S.L. and J. Liu designed and performed most of the experiments and analysed the data; X.W. performed most of the theoretical calculations and analysis (GW-BSE, STE, photoluminescence) under the guidance of Y.Y.; S.L. discovered the phosphor; L.Y. contributed in electroluminescence device optimization; L.G. carried out transient-absorption experiments; M.L. assisted in data analysis and photoluminescence measurements; Y.G. and J.E. carried out the electron microscopy measurements and analysed the results; Y.F. and L.Z. simulated the band alignment and the contour plots of the valence-band maximum and conduction-band maximum charge densities; C.Z. and S.J. provided some optical measurements; Q.D., F.M., L.W., W.L. and J.H. helped in the PLQY measurement and electroluminescence device fabrication; G.N. was involved in data analysis and experimental design; J.W. contributed to DFT calculations, Y.Y. helped in manuscript writing; J. Luo, X.W., E.H.S. and J.T. wrote the paper; all authors commented on the manuscript.
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Extended data figures and tables
Extended Data Fig. 1 Phonon band structure of Cs2AgInCl6 and the zone-centre Jahn–Teller phonon mode (inset).
The phonon band structure was calculated by the finite-difference method with the supercell approach. The consistency of the displacement pattern of the phonon eigenvector with that of the lattice distortion during STE formation, as well as the consistency of the phonon eigenfrequency with the phonon frequency fitted from the configuration coordinate diagram, confirm that the Jahn–Teller phonon mode coupled with the photoexcited excitons is responsible for the STE formation in Cs2AgInCl6.
Extended Data Fig. 2 Emission characterization of pure Cs2AgInCl6.
a, The broad photoluminescence (PL) spectrum of Cs2AgInCl6 measured at room temperature. b, Temperature-dependent photoluminescence spectra of pure Cs2AgInCl6. c, Fitting results of the FWHM as a function of temperature. We note that we used a relatively low-temperature region to avoid the influence of defect-assisted emission. d, The PLQY of Cs2AgInCl6. The reference was measured in an integrating sphere with a blank quartz plate.
Extended Data Fig. 3 Electronic and optical properties of Cs2NaInCl6.
a, GW-calculated band structure. The GW bandgap is 6.42 eV. The lowest exciton, with a binding energy of 0.8 eV, is dark. The first bright exciton has a binding energy of 0.44 eV. b. Calculated optical absorption (‘Abs-theory’) and photoluminescence (‘PL-theory’) spectra are compared with experimental results (‘Abs-exp.’ and ‘PL-exp.’).
Extended Data Fig. 4 Alloy behaviour of Cs2AgxNa1−xInCl6.
a, XRD patterns of Cs2AgxNa1−xInCl6, shifted to lower degrees with increasing sodium substitution (theta, diffraction angle). b, Refined lattice parameter, plotted as a function of the nominal x in Cs2AgxNa1−xInCl6, showing a linear increase with increased sodium substitution (see Supplementary Fig. 3 for details of the characterization). We note that selected-area electron diffraction and scanning electron nanobeam diffraction analysis results (Supplementary Figs. 4, 5) suggest the existence of a microscopic super-lattice (Na/Ag ordering).
Extended Data Fig. 5 Photoluminescence enhancement of doped double-perovskite powders.
a, Photoluminescence spectra of pure Cs2AgInCl6 and Li-doped Cs2AgInCl6. b, Photoluminescence spectra of pure Cs2AgSbCl6 and Na-doped Cs2AgSbCl6.
Extended Data Fig. 6 Characterization of the effect of Bi doping on Cs2AgxNa1−xInCl6.
a, High-resolution single-crystal XRD of the (111) peaks of Cs2Ag0.60Na0.40InCl6 with and without Bi doping. b, Absorption spectra of various materials with and without Bi doping for wavelengths of 500–950 nm. c, PLQY results. d, Photoluminescence lifetime. e, Comparison of the total density of states (DOS) between pure and Bi-doped Cs2AgInCl6. The inset shows the band alignment of pure and Bi-doped Cs2AgInCl6. CBM, conduction band minimum; VBM, valence band maximum. The small shallow peak marked by an arrow is derived from the Bi 6s states, which hybridize with the Ag 4d states. f, Partial density of states (PDOS) of Bi-doped Cs2AgInCl6.
Supplementary information
Supplementary Information
This file contains the Supplementary Tables (Tables S1–S4) and Supplementary Discussion (Figs. S1–S17) which include: XRD analysis of alloyed Cs2AgxNa1−xInCl6 powder, inductively coupled plasma optical emission spectrometer (ICP-OES) results of Cs2AgxNa1−xInCl6 with Bi doping, electron microscopy and diffraction results of a small fraction of Cs2Ag0.60Na0.40InCl6, optical characterization of Cs2AgxNa1−xInCl6 powder, and the film morphology, device performance and further improving strategies for thermally evaporated Cs2Ag0.60Na0.40InCl6 electroluminescent devices
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Luo, J., Wang, X., Li, S. et al. Efficient and stable emission of warm-white light from lead-free halide double perovskites. Nature 563, 541–545 (2018). https://doi.org/10.1038/s41586-018-0691-0
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DOI: https://doi.org/10.1038/s41586-018-0691-0
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