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Two-dimensional-lattice-confined single-molecule-like aggregates

Dou, Letian
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Data availability

Crystallographic data for the structure of FBTT-contained and FBTP-contained 2D SLs reported in this article have been deposited at the Cambridge Crystallographic Data Centre under deposition numbers CCDC 2289715 and 2283333, respectively. Copies of the data can be obtained free of charge at https://www.ccdc.cam.ac.uk/structures/ . All other data supporting the findings of this study are available in the article and its Supplementary Information . Source data are provided with this paper.

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Acknowledgements

This work is supported by the National Science Foundation (grant nos. 2131608-ECCS and 2143568-DMR). A.D. acknowledges the support for spectroscopy measurements from the US Department of Energy, Office of Science, Office of Basic Energy Sciences under award no. DE-SC0022082. Z.-Y.L. and B.M.S. acknowledge the support for MD simulations from the US Department of Energy, Office of Energy Efficiency and Renewable Energy (EERE) under the Solar Energy Technologies Office award DE-EE0009519. The views expressed herein do not necessarily represent the views of the US Department of Energy or the United States Government. Work at Yale was supported by the Air Force Office of Scientific Research under grant no. FA9550-22-1-0209. C.B.F., A.B. and V.M.S. acknowledge the support of the Office of Naval Research (ONR) under award no. N00014-21-1-2026 and the Air Force Office of Scientific Research under grant no. FA9550-22-1-0372. We thank J. Simon for establishing the angle-dependent PL setup, Q. Hu for the help with mass-spectrometry measurements, L. Huang and M. Gather for discussions, and H. Liu for spatial-coherence measurements.

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Authors and Affiliations

  1. Davidson School of Chemical Engineering, Purdue University, West Lafayette, IN, USA

    Kang Wang, Zih-Yu Lin, Wenhao Shao, Hanjun Yang, Yuanhao Tang, Dharini Varadharajan, Brett M. Savoie & Letian Dou

  2. Key Laboratory of Photochemistry, Institute of Chemistry, Chinese Academy of Sciences, Beijing, China

    Kang Wang, Zehua He & Yong Sheng Zhao

  3. Department of Chemistry, Purdue University, West Lafayette, IN, USA

    Angana De, Hanjun Yang & Letian Dou

  4. Department of Chemical & Environmental Engineering, Yale University, New Haven, CT, USA

    Conrad A. Kocoj & Peijun Guo

  5. Energy Sciences Institute, Yale University, West Haven, CT, USA

    Conrad A. Kocoj & Peijun Guo

  6. Advanced Light Source, Lawrence Berkeley National Laboratory, Berkeley, CA, USA

    Aidan H. Coffey & Chenhui Zhu

  7. Elmore Family School of Electrical and Computer Engineering, Purdue University, West Lafayette, IN, USA

    Colton B. Fruhling, Alexandra Boltasseva & Vladimir M. Shalaev

  8. Birck Nanotechnology Center, Purdue University, West Lafayette, IN, USA

    Colton B. Fruhling, Alexandra Boltasseva, Vladimir M. Shalaev & Letian Dou

Authors

  1. Kang Wang

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  2. Zih-Yu Lin

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  3. Angana De

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  4. Conrad A. Kocoj

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  5. Wenhao Shao

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  6. Hanjun Yang

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  7. Zehua He

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  8. Aidan H. Coffey

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  9. Colton B. Fruhling

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  10. Yuanhao Tang

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  11. Dharini Varadharajan

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  12. Chenhui Zhu

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  13. Yong Sheng Zhao

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  14. Alexandra Boltasseva

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  15. Vladimir M. Shalaev

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  16. Peijun Guo

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  17. Brett M. Savoie

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  18. Letian Dou

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Contributions

L.D. conceived the idea. L.D. and B.M.S. supervised the project. K.W. carried out the materials synthesis, structural characterizations, film fabrication and data analysis. Z.-Y.L. and B.M.S. performed MD simulations and data analysis. A.D. conducted the low-temperature PL and time-resolved PL measurements and data analysis. C.A.K. and P.G. carried out streak-camera measurements. W.S. helped with DFT calculations on band alignment. H.Y. carried out FLIM measurements and data analysis. Z.H. and Y.S.Z. helped with DBR device fabrication and lasing characterizations. A.H.C. and C.Z. performed GIWAXS measurements. Y.T. conducted FTIR spectroscopy measurements. A.B. and V.M.S. supervised the optical-characterization-related activities and C.B.F. conducted angle-resolved PL measurements. D.V. contributed to ligand design and synthesis. K.W. and L.D. wrote the manuscript. All authors discussed the results and revised the manuscript.

Corresponding authors

Correspondence to Brett M. Savoie or Letian Dou .

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Extended data figures and tables

Extended Data Fig. 1 DFT and TDDFT simulation on the energy level of molecular emitters.

a , Molecular structures of four different organic emitters. b , The calculated HOMO–LUMO and S1 level of organic molecules relative to the valance band maximum (VBM)–conduction band minimum (CBM) of lead-bromide matrix. The VBM–CBM value of [PbBr 4 ] 2− was adapted from the literature 39 . c , Scheme of the band alignment in organic–inorganic perovskite 2D SL structures including type I, type II and reversed type I.

Extended Data Fig. 2 The extracted azimuthal distribution of GIWAXS intensity for 2D perovskites at a typical q near 0.5 A −1 (dashed rings in Fig. 2b,f ).

a , FBTT 2D SLs. b , FBTP 2D SLs. 0° and 180° correspond to the q xy plane (vertical orientation) and 90° corresponds to the q z direction (horizontal orientation). For the FBTT sample, it shows a peak scattering intensity of about 2,200 at 90°, which is very similar to that of FBTP (about 2,100). At 0° or 180°, FBTT shows substantial scattering with an intensity of about 410, whereas FBTP has a negligible scattering. Here the orientation factor was defined as the scattering intensity ratio between 0° (180°) and 90°, which yields a value of 0.19 and roughly 0 for FBTT and FBTP, respectively. A greater orientation factor value suggests a preferred orientation along the q xy direction, which corresponds to a vertically oriented [PbX 4 ] 2− inorganic sublattice relative to the substrate. Therefore, in our scenario, the FBTT sample is dominated by horizontal orientation with a small fraction of vertical orientation, whereas the FBTP sample exhibits an almost perfectly horizontal orientation.

Extended Data Fig. 3 FBTP emitters confined in 2D SLs with tunable inorganic sublattices.

a , PL spectra. b , UV–vis spectra. c , XRD of FBTP-contained 2D SLs with different halide compositions.

Extended Data Fig. 5 2D perovskite nanocrystals and their corresponding PL spectra.

a , (PEA) 2 PbBr 4 nanocrystal. b , (FBTT) 2 PbBr 4 nanocrystal. c , (FBTP) 2 PbBr 4 nanocrystal. The scale bars are 5 μm. The PEA sample shows a square shape with violet emission from the [PbBr 4 ] 2− inorganic sublattice, which is consistent with the results from the literature 58 , demonstrating the successful growth of single-crystalline (PEA) 2 PbBr 4 2D perovskite. By replacing the PEA with FBTT or FBTP, we also obtained rectangular nanocrystals using a similar crystal-growth procedure, implying the formation of single-crystalline FBTT-based and FBTP-based 2D perovskite nanocrystals. Moreover, FBTT-based and FBTP-based nanocrystals exhibit strong orange and green emission, respectively, which is probably from the organic molecules. By taking a closer look at their PL spectra, we found that the PL peak of the (FBTT) 2 PbBr 4 nanocrystal is closer to that of FBTT aggregates, whereas the PL peak of the (FBTP) 2 PbBr 4 nanocrystal closely resembles that of FBTP monomer. These findings align well with our observations from thin-film samples, thus ruling out the influence of crystallinity on different emission properties.

Extended Data Fig. 6 Schematic illustration of MD simulations on organic molecules rotation in the perovskite lattice.

a , FBTT-contained 2D SLs. b , FBTP-contained 2D SLs. The dashed boxes highlight the molecules under rotation investigation.

Extended Data Fig. 7 The packing styles of organic molecules within 2D SLs.

a , View down the long molecular axis of FBTT molecules in the SLs, which clearly demonstrates a traditional herringbone packing style. b , View down the long molecular axis of partial FBTP molecules in the SLs, revealing a new molecular packing style. H atoms and inorganic sublattices are omitted for clarity.

Extended Data Fig. 8 Structural characterizations and UV–vis spectra of PBTP-based and BBTP-based thin films.

XRD ( a ) and GIWAXS ( b , c ) patterns for perovskite thin films incorporated with PBTP ( b ) and BBTP ( c ) molecules. XRD and out-of-plane ( q z ) GIWAXS patterns help us verify that both PBTP and BBTP have been successfully incorporated into the lead-bromide matrix, forming a layered structure. The in-plane spacing is determined to be 5.98 and 5.76 Å from the q xy direction at 1.05 and 1.09 Å −1 for PBTP and BBTP (similar to the 3D perovskite lattice), respectively, which indicates that the 2D structures of these organic emitters incorporated 2D SLs. d , UV–vis spectra of PBTP-doped PMMA (monomers), neat PBTP aggregates and PBTP 2D SLs films. e , UV–vis spectra of BBTP-doped PMMA (monomers), neat BBTP aggregates and BBTP 2D SLs films. The sharp UV–vis peak around 400 nm and the nearby shoulder peak from 2D SLs films can be indexed to the excitonic peak of perovskites and organic emitters, respectively, further supporting the formation of 2D perovskite SLs.

Extended Data Fig. 9 Streak-camera results at different temperatures.

a , b , FBTP monomers at 250 K ( a ) and 150 K ( b ). c , d , FBTP 2D SLs at 250 K ( c ) and 150 K ( d ). After carefully examining our FBTP SL sample and its spectroscopic features, we found several reasons to rule out the dispersive energy transfer explanation 64 , 65 . (1) Our organic emitters in the perovskite lattice are the identical molecules, typically exhibiting homogeneous energy distribution. This is different from the conjugated polymer cases, which show dispersive energy transfer from high-energy sites to low-energy sites owing to the inhomogeneously broadened density of states with different effective conjugation length. (2) Forster-type energy transfer usually requires effective spectral overlap between the absorption and emission spectra. The spectral overlap is minimal in our 2D SL system (Fig. 1g and Supplementary Fig. 5c ), which may result in the dispersive energy transport being less effective. Furthermore, the excitation wavelengths used for time-resolved PL and streak-camera measurements are 447 and 440 nm, respectively, which are near the tail end of the absorption band. This suggests that the dispersive energy transfer is unlikely to play a notable role in the observed bathochromic shift over time. (3) If the dispersive energy transport were occurring in FBTP 2D SLs, the PL spectra would be expected to continuously redshift and reach a stationary energy in a nanosecond timescale. By contrast, our streak-camera results (Fig. 5e and Extended Data Fig. 9c,d ) show redshifting only within about 100 ps. More importantly, the final emission state reached in FBTP SLs is exactly the same as that of the FBTP monomer (Fig. 5d and Extended Data Fig. 9a,b ). This behaviour implies that the emerging rapid decay at the short-wavelength side originates from the high-energy emission state (that is, locally excited state), rather than from the high-energy fraction of the emitters (broadened density of states).

Extended Data Fig. 10 Lasing characterization on FBTP monomer and FBTP aggregates.

a , Experimentally measured reflectance spectra for DBRs, in which the pump laser was directed into the device from the top DBR to excite the sample, followed by the collection of emission from the same side. The wavelength range of the top DBR with high reflectance (>98%) fully covers the optical gain region of FBTP monomer, 2D SLs and aggregates. b , Simulated transmittance spectra of a 2D SLs-based DBR device, which matches well with the lasing spectra from this device. Inset, electric-field distribution of the 536-nm optical standing wave inside the device. c , PL images of a 2D SLs-based DBR device with pump fluence below, near and above the threshold. Scale bar, 100 μm. d , PL spectra evolution of FBTP monomer under different pump fluences. e , Corresponding PL intensity against increasing pump fluences in log–log scale, showing a clear ‘kink’ at a threshold energy density of 2.71 μJ cm −2 . The superlinear intensity dependence is fitted to a power law x p with p mon = 1.70 above the threshold. f , PL spectra evolution of FBTP aggregates under different pump fluences. g , Corresponding PL intensity against increasing pump fluences in log–log scale, which reveals linear ( p agg = 1.01) and sublinear ( p agg = 0.78) growth across a broad pump fluence range, suggesting the absence of lasing from FBTP aggregates.

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Wang, K., Lin, ZY., De, A. et al. Two-dimensional-lattice-confined single-molecule-like aggregates. Nature (2024). https://doi.org/10.1038/s41586-024-07925-9

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