Colloidal lead halide perovskite nanocrystals have potential for lighting applications due to their optical properties. Precise control of the nanocrystal dimensions and composition is a prerequisite for establishing practical applications. However, the rapid nature of their synthesis precludes a detailed understanding of the synthetic pathways, thereby limiting the optimisation. Here, we deduce the formation mechanisms of anisotropic lead halide perovskite nanocrystals, 1D nanorods and 2D nanoplatelets, by combining in situ X-ray scattering and photoluminescence spectroscopy. In both cases, emissive prolate nanoclusters form when the two precursor solutions are mixed. The ensuing antisolvent addition induces the divergent anisotropy: The intermediate nanoclusters are driven into a dense hexagonal mesophase, fusing to form nanorods. Contrastingly, nanoplatelets grow freely dispersed from dissolving nanoclusters, stacking subsequently in lamellar superstructures. Shape and size control of the nanocrystals are determined primarily by the antisolvent's dipole moment and Hansen hydrogen bonding parameter. Exploiting the interplay of antisolvent and organic ligands could enable more complex nanocrystal geometries in the future.

Structure

The data is organised in one folder per experimental technique with a separate folder for the code for data analysis.

code_for_data_analysis

contains Jupyter notebooks (*.ipynb) and toolbox_kf.py with helper functions for an in situ SAXS, WAXS, and PL analysis as presented in Figures 2, 3 and 4. The SAXS model for precursor micelles and ellipsoidal intermediate nanoclusters for SasView and .sh/.py scripts for batch fitting are additionally provided.

• 05_run19.sh is a shell script for running a SAXS batch fit.
• 05_run19_css_at_hs_plus_ellipsoid_unbinned_subcorr_all.config contains the fit configuration (data paths, initial parameters, optimiser settings) for a SAXS batch fit.
• core_shell_sphere_at_hardsphere_plus_ellipsoid.py contains the model instructions for SasView.
• Figure_02.ipynb contains the PL and WAXS analysis for Figure 2.
• Figure_03.ipynb contains the SAXS analysis for Figure 3.
• Figure_04.ipynb contains the PL and SAXS analysis for Figure 4.
• ssv.py is a python script for batch fitting with SasView using the settings from the .config file.
• toolbox_kf.py contains helper functions.

ex_situ_PL

• Fig01d.xlsx contains the ex situ PL spectra shown in Figure 1 d.

in_situ_PL

• 2023-11-10_2ML_acetone_02.h5 contains the in situ PL data of a 2ML nanoplatelet synthesis shown in Figure 4 f and g.
• kf_run13_5ml_00001_000023.h5 contains the in situ PL data of a 3ML nanorod synthesis (accidentally mislabelled as 5ml) shown in Figure 2 b and d.
• run13_3ML_c0.h5 contains the in situ PL data of a 3ML nanorod synthesis shown in Figure 4 b and c.

.h5 files can be opened e.g. with h5py in python. entry/instrument/detector/spectra and entry/instrument/detector/wavelength contain the intensities and wavelengths, respectively.

in_situ_SAXS

• acetone_run.zip contains the raw SAXS data (detector images) of the acetone background.
• kf_agbh_1s_for_insitu_sdetx50.zip contains the raw SAXS data of silver behenate for calibration of the detector position.
• run09_3ML.zip contains the raw in situ SAXS data of a 3ML nanorod synthesis shown in Figure 4 a and c.
• run15_2ML_c0.zip contains the raw in situ SAXS data of a 2ML nanoplatelet synthesis shown in Figure 4 e and g.
• run19_2ML_c0.zip contains the raw in situ SAXS data of a 2ML nanoplatelet synthesis shown in Figure 3 a, b, d and e.
• run24_3ML_CsOl_18_235_12.zip contains the raw in situ SAXS data of a 3ML nanorod synthesis shown in Figure 3 d and e.
• toluene_run.zip contains the raw SAXS data of the toluene background.
• frame_number_transmission_syringe_motion.zip contains .dat files with the frame number, the sample transmission and the syringe motion, saved for each detector frame. A short drop or rise in the syringe motion value indicates movement of the syringe. The first syringe injects Cs-oleate, the second one acetone. run19_2ML_c0 and run24_3ML_CsOl_18_235_12 have been cut to the first 400 frames (20 s), which contain the formation of intermediate nanoclusters.
• motions_indices.zip contains .dat files with only the frame numbers for which a syringe motion was detected. Frame indices start at 0. The first number indicates the first frame in which motion was detected, the second number indicates the first frame in which no motion was detected anymore.
• saxs_binned_subtracted.zip contains the in situ SAXS data used for Figure 4 after binning of ten frames, azimuthal integration, normalisation, and subtraction of the toluene and acetone backgrounds. The processing steps are described in the header of the .dat files. These are the data used for analysis of the mesophases as I(q) vs q.
• saxs_unbinned_subtracted.zip contains the in situ SAXS data used for Figure 3 after azimuthal integration, normalisation, and subtraction of the toluene and acetone backgrounds. The processing steps are described in the header of the .dat files. These are the data used for analysis of the transformation of precursor micelles to intermediate nanoclusters as I(q) vs q.

.h5 and .nxs files can be opened e.g. with h5py in python. Loading hdf5plugin before h5py might be required. The files ending in /_master.h5 contain links to the data files (/entry/data). Each data file contains up to 100 detector images. The file ending in .nxs contains a link to the data (/scan/data/saxs_raw) as well as additional metadata.

in_situ_WAXS

• kf_insitu_04_lab6_65_00002.zip contains the raw WAXS data (detector images) of LaB6 for calibration of the detector position.
• kf_insitu_cell_02_acetone_00001.zip contains the raw WAXS data of the acetone background.
• kf_insitu_cell_02_toluene_00002.zip contains the raw WAXS data of the toluene background.
• kf_run13_5ml_00001.zip contains the raw in situ WAXS data of a 3ML nanorod synthesis shown in Figure 2 c and d.
• kf_run13_5ml_00001.dat contains the frame numbers of the syringe motions. pump1 is for Cs-oleate injection, pump2 is for acetone injection. Frame indices start at 0. The first number indicates the first frame in which motion was detected, the second number indicates the first frame in which no motion was detected anymore.
• subtracted_varex_data.zip contains the in situ WAXS data used for Figure 2 after azimuthal integration and subtraction of the toluene and acetone backgrounds. The processing steps are described in the header of the .dat files. These are the data used for analysis of the nucleation of intermediate nanoclusters.

32 bit .tif files can be opened e.g. with ImageJ or pyFAI.

TEM

contains the TEM images of purified 2ML CsPbBr3 nanoplatelets and 3ML CsPbBr3 nanorods shown in Figure 1 c and the TEM image and FFT of intermediate nanoclusters shown in Figure 3 f and g.

.tif files can be opened e.g. in ImageJ or DigitalMicrograph/Gatan Microscopy Suite.

Contact

Corresponding authors: Alexander S. Urban (urban@lmu.de), Bert Nickel (nickel@lmu.de)