All-Perovskite Multicomponent Nanocrystal Superlattices

Nanocrystal superlattices (NC SLs) have long been sought as promising metamaterials, with nanoscale-engineered properties arising from collective and synergistic effects among the constituent building blocks. Lead halide perovskite (LHP) NCs come across as outstanding candidates for SL design, as they demonstrate collective light emission, known as superfluorescence, in single- and multicomponent SLs. Thus far, LHP NCs have only been assembled in single-component SLs or coassembled with dielectric NC building blocks acting solely as spacers between luminescent NCs. Here, we report the formation of multicomponent LHP NC-only SLs, i.e., using only CsPbBr3 NCs of different sizes as building blocks. The structural diversity of the obtained SLs encompasses the ABO6, ABO3, and NaCl structure types, all of which contain orientationally and positionally locked NCs. For the selected model system, the ABO6-type SL, we observed efficient NC coupling and Förster-like energy transfer from strongly confined 5.3 nm CsPbBr3 NCs to weakly confined 17.6 nm CsPbBr3 NCs, along with characteristic superfluorescence features at cryogenic temperatures. Spatiotemporal exciton dynamics measurements reveal that binary SLs exhibit enhanced exciton diffusivity compared to single-component NC assemblies across the entire temperature range (from 5 to 298 K). The observed coherent and incoherent NC coupling and controllable excitonic transport within the solid NC SLs hold promise for applications in quantum optoelectronic devices.

temperature with an ice-water bath.The crude solution was centrifuged at 12100 rpm (20130 rcf) for 5 min, the supernatant was discarded, and the precipitate was dispersed in 0.3 ml of anhydrous hexane.The solution was centrifuged again at 10000 rpm (13780 rcf) for 3 min, and the precipitate was discarded.Then, OLA/OA ligands were exchanged by DDAB treatment.For that, 0.3 ml of anhydrous hexane, 0.6 ml of anhydrous toluene, and 0.14 ml of 0.05M DDAB solution in toluene were added to the supernatant.The solution was then stirred for hour, followed by destabilization with 1.8 ml of ethyl acetate, centrifugation at 12100 rpm (20130 rcf) for 3 min, and redispersion in 0.6 mL of anhydrous toluene.
Synthesis of 14-18 nm CsPbBr3 NCs, adapted from Ref. 5 In a 25 mL three-neck flack, 44.6 mg of PbO (0.2 mmol), 119.4 mg of phenacyl bromide (0.6 mmol), 1 ml of OA (vacuum-dried at 100 °C) were loaded and suspended in 5 ml of ODE.The temperature was increased to 220 °C, and 0.6 ml of oleylamine (distilled) was injected into the reaction mixture.The solution initially became red, then gradually turned orange and yellow in ~10 min.The temperature was decreased to 210 °C and 0.5 ml of 0.12M Cs-OA solution in ODE (preheated to about 100 °C) was swiftly injected into the bright yellow solution.The solution was annealed for 1 h at 210 °C and then cooled down to room temperature with an ice-water bath.The crude solution was centrifuged at 3000 rpm (1240 rcf) for 5 min, the dark-brown supernatant was discarded, and the precipitate was redispersed in 2 ml of toluene.The solution was centrifuged a second time at 3000 rpm (1240 rcf) for 3 min, and the precipitate was discarded.The OLA-OA ligands were exchanged by DDAB/PbBr2 treatment.DDAB+PbBr2 stock solution was prepared by dissolving 36.7 mg (0.1 mmol) PbBr2 and 92 mg (0.2 mmol) DDAB in 3 mL of anhydrous toluene.60 µl of DDAB/PbBr2 solution was added to the NC dispersion.The solution was then stirred for 1 h, followed by destabilization with 1.2 ml of ethyl acetate, centrifugation at 12100 rpm (20130 rcf) for 2 min, and redispersion in 0.4 ml of toluene.Smaller 14.2 nm CsPbBr3 NCs were obtained by annealing at a lower temperature (205 °C).The packing density for fcc-packed spherical NCs is given as a grey dashed line.The spacefilling curves for ABO3 and ABO6-type SLs were plotted within OTM, while the curve for NaCltype was constructed using the hard-sphere model. 6The packing density η is calculated as the volume fraction occupied by the NCs in the SL, leaving (1-η) as voids.Rhombicuboctahedral CsPbBr3 NCs have a high tendency to behave like spherical NCs during self-assembly.Therefore, in the calculation of packing density for the CsPbBr3-CsPbBr3 SLs their shape was approximated as spherical.The packing densities for all experimentally chosen γ values exceed the packing density for the fcc lattice (η = 0.74), thus theoretically confirming their formability.

Figure S1 .
Figure S1.NC building blocks for SL.(a) TEM image of 5.3 nm CsPbBr3 NC monolayer with (d) the corresponding absorption and PL spectra of the NC solution in toluene.(b) TEM image of 8.0 nm CsPbBr3 NC monolayer with (e) the corresponding absorption and PL spectra of the NC solution in toluene.(c) TEM image of 17.7 nm CsPbBr3 NC monolayer with (f) the corresponding absorption and PL spectra of the NC solution in toluene.As elaborated elsewhere, 3 5.3 nm CsPbBr3 NCs exhibit unusual rhombic packing with an obtuse angle of ~104 o , while 8.0 nm NCs preserve typical square ordering. 1The 26-faceted 17.7 nm CsPbBr3 NCs post-treated with DDAB are packed in a hexagonal lattice.

Figure S2 .
Figure S2.Faceting of rhombicuboctahedral CsPbBr3 NCs.(a) HRTEM image of a NC viewed along [100]NC with (b) the corresponding structural model.(c) HRTEM image of a NC viewed along [110]NC with (d) the corresponding structural model.As evidenced by HRTEM images of NCs oriented along two crystallographic directions, the synthesized large-component CsPbBr3 NCs exhibit a faceted rhombicuboctahedral shape.

Figure S3 .
Figure S3.Minor orientations of rhombicuboctahedral CsPbBr3 NCs in a single-component SL.(a) Structural model of the fcc-type unit cell with one NC rotated by 45° about the [001]SL zone-axis and (d) ED pattern with the corresponding reflections for this orientation (highlighted in magenta).(b) Structural model of the fcc-type unit cell with one NC, first, rotated by 45° about [010]SL, then by 45° about the [001]SL zone-axis, and (e) ED pattern with the corresponding reflections for this orientation (highlighted in yellow).(c) Structural model of the fcc-type unit cell with one NC, first, rotated by 45° about [010]SL, then by -45° about the [001]SL zone-axis, and (e) ED pattern with the corresponding reflections for this orientation (highlighted in green).The orientation in (a) is easily identifiable by the presence of a characteristic 110 reflection at 45° from the same reflection of the major orientation.The orientations in (b) and (c) are detected by the presence of 111 reflections, which are absent for the major orientation.

Figure
Figure S4.Space-filling curves of NaCl-(red), ABO3-(blue), and ABO6-(yellow) type binarySLs assembled from cubic and spherical NCs, with experimentally observed points depicted as circles.The packing density for fcc-packed spherical NCs is given as a grey dashed line.The spacefilling curves for ABO3 and ABO6-type SLs were plotted within OTM, while the curve for NaCltype was constructed using the hard-sphere model.6The packing density η is calculated as the volume fraction occupied by the NCs in the SL, leaving (1-η) as voids.Rhombicuboctahedral CsPbBr3 NCs have a high tendency to behave like spherical NCs during self-assembly.Therefore, in the calculation of packing density for the CsPbBr3-CsPbBr3 SLs their shape was approximated as spherical.The packing densities for all experimentally chosen γ values exceed the packing density for the fcc lattice (η = 0.74), thus theoretically confirming their formability.

Figure S5 .
Figure S5.Structural characterization of ABO6-type SL.(a) Structural model of a small area of the [001]SL-oriented ABO6-type SL domain.(b) Averaged HAADF-STEM image with (c) the corresponding line profile revealing the presence of two small O-site cubes positioned along the line between larger rhombicuboctahedral NCs.(d) HAADF-STEM image of [001]SL-oriented domain showing the initial SL orientation with (inset) the corresponding structural model.(e) HAADF-STEM image of [101]SL-oriented domain after tilting the substrate by 45° about [010]SL with (inset) the corresponding structural model.

Figure S6 .
Figure S6.ABO6-type SL on SiN substrates.(a and b) Low-magnification TEM images of ABO6type SL domains on Norcada SiN windows.(c) A close-up BF-STEM image of one of the SL domains.The images illustrate the extended SL domain coverage over SiN windows selected for subsequent optical measurements.

Figure S7 .
Figure S7.GIWAXS and GISAXS data for single-component and ABO6-type SLs.Azimuthalintegrated 1D pattern in the WAXS region for (a) ABO6-type SL and (c) single-component SL from 17.7 nm CsPbBr3 NCs.Black ticks mark the theoretical hkl reflections for CsPbBr3 with an orthorhombic crystal structure.CsPbBr3 NCs in both SL types preserve the orthorhombic crystal structure, with the inclusion of the CsPb2Br5 phase possibly as the result of sample aging (peak at Q=0.85 Å, denoted as an asterisk).(b) The correlation between measured GISAXS reflections (green circles) and computed reflections (black asterisks) for ABO6-type SL.The reflections are well-correlated, confirming the proposed cubic packing of larger NCs in the ABO6-type SL, with unit cell edge of ca.21 nm.

Figure S8 .
Figure S8.NaCl-type CsPbBr3-CsPbBr3 SL comprising 8.5 nm and 17.6 nm CsPbBr3 NCs.(a) TEM image of [001]SL-oriented NaCl-type SL domain with the unit cell shown in the inset.(b) Corresponding WAED pattern with the most intense reflections marked; superimposed reflections for 8.5 nm and 17.6 nm CsPbBr3 NCs are shown in yellow and blue, respectively; indeed, the absence of extra peaks or Debye-Scherrer rings evidence the equioriented small and large NC SL components; (inset) structural model of a [001]SL-oriented NaCl-type SL.(c) HAADF-STEM image of [001]SL-oriented NaCl-type SL domain and (d) HAADF-STEM image of its monolayer confirming the formation of the binary SL.

Figure S9 .
Figure S9.ABO3-type CsPbBr3-CsPbBr3 SL comprising 8.5 nm and 14.2 nm CsPbBr3 NCs.(a) TEM and (c) BF-STEM images of the [001]SL-oriented ABO3-type SL with (inset in c) the structural model of a unit cell.(b) The corresponding WAED pattern with the most intense reflections for 8.5 nm and 14.2 nm CsPbBr3 NCs marked in yellow and blue, respectively; (inset) structural model of a [001]SL-oriented ABO3-type SL.(d) HAADF-STEM image of the ABO3type SL domain resembling [101]SL orientation with the corresponding structural model (inset).The high degree of orientational ordering is demonstrated in the WAED by the presence of sharp arcs corresponding to 110 and 200 reflections of A-site rhombicuboctahedra and B-site cubes, as well as by 111 reflections of O-site cubes.

Figure S10 .
Figure S10.Segregation of 8.5 nm and 14.5 nm CsPbBr3 NCs.TEM images showing the segregation of cubic-shaped 8.5 nm and 14.5 nm CsPbBr3 NCs into single-component SLs during the co-assembly process.

Figure S11 .
Figure S11.Time-resolved PL spectroscopy of reference NC samples in a weak excitation regime at a cryogenic temperature (6 K). (a and d) PL spectra for 5.3 nm and 17.6 nm CsPbBr3 NCs, respectively, under different excitation intensities.(b and e) Fluence dependence of the PL peak intensity for 5.3 nm and 17.6 nm CsPbBr3 NCs, where the solid lines denote power law fits with exponents of 1.00 and 0.95, respectively.(c and f) Spectrally integrated time-resolved emission intensity traces at different excitation intensities.

Figure S12 .
Figure S12.Time-resolved PL spectroscopy of ABO6-type SL in a weak excitation regime at a cryogenic temperature (6 K).(a) PL spectra for ABO6-type SL under different excitation intensities.(c) Fluence dependence of the PL peak intensity for red and blue peaks where the solid lines denote power law fits with exponents of 0.95 and 1.04, respectively.(b and d) Spectrally integrated time-resolved emission intensity traces at different excitation intensities for red and blue peaks, respectively.A drastic change in the 5.3 nm NCs (donor) lifetime in all-perovskite SLs compared to the reference sample (FigureS11c), attests to the occurrence of an efficient energy transfer also at cryogenic temperatures, in agreement with room temperature results obtained by pump-probe spectroscopy.

Figure S13 .
Figure S13.PL (in logarithmic scale) and PLE spectra obtained at 10 K from ABO6-type SL.The PLE spectrum was obtained while monitoring the emission peak of the 17.6 nm NC component of the SL and contains a feature at ~2.45 eV matching the energy position and spectral shape of the 5.3 nm NC emission.The coincidence of the PL and PLE peaks confirm that the 17.6 nm NCs (energy acceptors) are effectively excited via energy funneling from the 5.3 nm NCs (energy donors).

Figure S14 .
Figure S14.Hyperspectral PL mapping experiments at cryogenic temperature (10 K), performed on a ABO6-type binary SL and a disordered film comprising 5.3 nm and 17.6 nm NCs.(a) Schematic of the custom-made confocal PL mapping setup.(b) PL spectra from different probed areas across the two samples.In parts of the disordered film, strong emission from 5.3 nm NCs is observed as a result of partial segregation of small and large NCs within the film.On the contrary, very similar PL spectral characteristics, characterized by quenched 5.3 nm NC emission and strong 17.6 nm NC luminescence were obtained across the whole surface of the SL sample.The significantly more uniform distribution of the emission and energy in the SL sample is further evidenced by hyperspectral maps of the two samples, plotting: (c) PL peak wavelength and (d) PL intensity at the emission region of the 5.3 nm (donor) and 17.6 nm (acceptor) NCs.