Abstract
Environmentally friendly tin (Sn) perovskites have received considerable attention due to their great potential for replacing their toxic lead counterparts in applications of photovoltaics and light-emitting diodes (LEDs). However, the device performance of Sn perovskites lags far behind that of lead perovskites, and the highest reported external quantum efficiencies of near-infrared Sn perovskite LEDs are below 10%. The poor performance stems mainly from the numerous defects within Sn perovskite crystallites and grain boundaries, leading to serious non-radiative recombination. Various epitaxy methods have been introduced to obtain high-quality perovskites, although their sophisticated processes limit the scalable fabrication of functional devices. Here we demonstrate that epitaxial heterodimensional Sn perovskite films can be fabricated using a spin-coating process, and efficient LEDs with an external quantum efficiency of 11.6% can be achieved based on these films. The film is composed of a two-dimensional perovskite layer and a three-dimensional perovskite layer, which is highly ordered and has a well-defined interface with minimal interfacial areas between the different dimensional perovskites. This unique nanostructure is formed through direct spin coating of the perovskite precursor solution with tryptophan and SnF2 additives onto indium tin oxide glass. We believe that our approach will provide new opportunities for further developing high-performance optoelectronic devices based on heterodimensional perovskites.
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Data availability
The data that support the findings of this study are available from the corresponding author upon reasonable request.
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Acknowledgements
This work is financially supported by the National Key Research and Development Program of China (2022YFA1204800), the National Natural Science Foundation of China (52233011, 61961160733, 61935017, 62134007, 62288102 and 12274067) and the Jiangsu Provincial Departments of Science and Technology (BE2022023 and BK20220010). We thank Y. Han, X. Huang and L. Wang for helpful discussions.
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Jianpu Wang and W.H. conceived the project. Jianpu Wang, J.C. and N.W. designed the experiments. H.M., N.C. and Y.T. carried out the device fabrication and characterization. J. Liu conducted the SEM characterization. Y.W. and J. Li carried out the STEM characterization under the supervision of D.Z. TEM measurements were conducted by J.C. and C. Zhu, who also analysed the data. Jiaqi Wang and Q.C. conducted the X-ray diffraction measurements. N.C. and L.Z. conducted the NMR measurements. H.S., C. Zhuo, S.W., P.Y. and Q.P. conducted the optical measurements. X.W. conducted the GIWAXS measurements under the supervision of X.L. The first draught of the manuscript was written by J.C., and N.W. and Jianpu Wang provided major revisions.
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Extended data
Extended Data Fig. 1 Characterizations of the heterodimensional-bilayer tin perovskites prepared with SnF2+Trp additives.
a, Top-view SEM images with different magnifications. The scale bars represent 1 μm. b, Cross-sectional iDPC-STEM image and the enlarged image with FFT analyses. The lattice constant of ∼0.63 nm is corresponding to the (100) interplanar spacing of the 3D tin iodide perovskite. The scale bars represent 10 nm. c, Cross-sectional DPC-STEM image. The lattice fringe with a spacing of ∼2.2 nm is corresponding to the (002) plane of the 2D (n = 2) tin iodide perovskite. The scale bar represents 20 nm. The dark region in the 3D perovskite layer can be attributed to the film degradation under electron beam exposure. d, Absorption and PL (front/back side excitation) spectra of the perovskite film. e, XRD pattern shows the co-existence of 3D and 2D perovskites. Octothorpe mask denotes the signal of ITO substrate. f, Comparison of (001) XRD peaks of 3D perovskite in our 2D/3D tin perovskite film and those of FASnI3, FA0.9Cs0.1SnI3, FA0.3Cs0.7SnI3 and CsSnI3 perovskites.
Extended Data Fig. 2 GIWAXS data analysis of the heterodimensional-bilayer tin perovskite film.
Schematic assignment of the GIWAXS patterns, suggesting that the 2D perovskites are mainly horizontally oriented. The strong Bragg spots suggest that the 3D perovskite has a highly-ordered and vertically-orientated crystal packing. The incident angles (α) of 0.1° and 0.3° corresponds to the penetration depth of 3-5 nm and > 100 nm, respectively.
Extended Data Fig. 3 Additional structure characterizations of the hetero-dimensional-bilayer tin perovskite film.
a, XRD patterns of the film before and after transfer. b, Top view SEM image of the film transferred on a TEM copper grid. The scale bar represents 1 μm. These results suggest that the transferred film has the same 2D/3D structure as the spin-coated film on an ITO substrate.
Extended Data Fig. 4 Analysis of the lattice alignment of 2D and 3D perovskites.
a-b, TEM images and corresponding SAED patterns of typical 2D (n = 1) (PEA)2SnI4 perovskite film with different positions (a) and (b). The SAED patterns are assigned to the triclinic (PEA)2SnI4 (ref. 13). The scale bars in TEM images represent 500 nm. c, Simulated ED patterns of the 3D, 2D (n = 1), and 3D/2D overlapped lattices viewed along the [001] direction. The lattice parameters were taken from the literature (ref. 11,13). It is shown that the diffraction spots of (110), (1\(\bar{1}\)0), and (200) planes of 3D perovskite are overlapped with those of (200), (020), and (220) planes of 2D perovskite respectively, which is consistent with our experimental data. This suggests that the lattices of our 3D and 2D perovskites are well-aligned in the in-plane direction.
Extended Data Fig. 5 Additional device characteristics of the heterodimensional-bilayer tin perovskite LEDs.
a, Angular distribution of the radiation intensity of device, which follows a Lambertian profile. b, EL spectra at different viewing angles. c, Histogram of peak EQEs. Statistics from 94 devices show an average peak EQE of 9.9% with a relative standard deviation of 8.4%.
Extended Data Fig. 6 Device characteristics of large-area tin perovskite LEDs.
a, Photograph of the fabricated large-area (70 mm2) device. b, Dependence of current density and radiance on voltage. c, EQE curve plotted against current density. The inset represents a photograph of the operating large-area device, which is taken by a security camera with NIR mode. d, Histogram of peak EQEs.
Extended Data Fig. 7 Characterizations of tin perovskite films and LEDs prepared from precursor solutions with a single additive.
a-b, Cross-sectional and top-view SEM images of the SnF2 (a) or Trp (b) based tin perovskite films. All scale bars represent 1 μm. c, Excitation-intensity-dependent PLQEs. d, Dependence of current density and radiance on voltage. e, EQE curves plotted against current density. f-g, In-situ absorption (f) and PL (g) spectra of the tin perovskite films based on Trp or SnF2 alone, which were measured during the spin-coating process. h, Absorption and back-side-excited PL spectra of the corresponding films measured during the annealing process.
Extended Data Fig. 8 In-situ optical spectra and SEM images of tin perovskite films with or without SnF2+Trp additives.
a-b, Contour plots (a) and line plots (b) of in-situ absorption of tin perovskite films with or without SnF2+Trp additives measured during the spin-coating process. Before nucleation, the absorption observed at ∼350 nm can be assigned to the [SnI3]nn- cluster formed in precursor solutions (Supplementary Fig. 4) (ref. 4). c, In-situ PL spectra of the films measured during the spin-coating process. The arrows indicate the crystallization evolution direction as the spin-coating time increases. d, In-situ absorption spectra of the films measured during the annealing process. e, Cross-sectional and top-view SEM images of the tin perovskite film without additives. The enlarged top-view SEM image shows that the ITO substrate is exposed at perovskite boundaries. All scale bars represent 1 μm. f, PL (front/back side excitation) spectra of the perovskite film without additive.
Extended Data Fig. 9 Chemical interaction characterizations.
a, Chemical structures of FA+, PEA+ and Trp. b, 1H NMR spectra of PEAI, FAI, and various mixtures containing PEAI and/or FAI. The ammonium protons of PEA+ and FA+ are obvious and well-resolved in the PEAI + FAI+SnI2 mixture but weak and broad in the PEAI + FAI+SnF2 mixture. c, 119Sn NMR spectra of SnF2 and various mixtures containing SnF2, showing that the SnF2-Trp interaction is stronger than those of SnF2-PEAI and SnF2-FAI in the precursor solution. d, 1H NMR spectra of Trp and various mixtures containing Trp. Upon mixing with other precursors, the N-H protons of Trp show a downfield shift, suggesting the Trp-precursor interactions.
Extended Data Fig. 10 Characterizations of tin perovskite films and LEDs prepared from precursor solutions with SnF2 and different amino acid additives.
a, Top view SEM images of the perovskite films. The chemical structures of amino acids are shown in black. The scale bars represent 1 μm. b, Cross-sectional SEM images of the perovskite films, which show bilayer structures. The scale bars represent 100 nm. c, XRD patterns. d-e, PL spectra excited from the front (d) and back (e) sides, respectively. f, EL spectra. g, Dependence of current density and radiance on voltage. h, EQE curves plotted against current density.
Supplementary information
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Supplementary Figs. 1–4.
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Min, H., Wang, N., Chen, N. et al. Spin coating epitaxial heterodimensional tin perovskites for light-emitting diodes. Nat. Nanotechnol. (2024). https://doi.org/10.1038/s41565-023-01588-9
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DOI: https://doi.org/10.1038/s41565-023-01588-9
