Cuboidal Supraparticles Self-Assembled from Cubic CsPbBr₃ Perovskite Nanocrystals

Abstract

Colloidal CsPbBr3 nanocrystals (NCs) have emerged as promising candidates for various opto-electronic applications, such as light-emitting diodes, photodetectors, and solar cells. Here, we report on the self-assembly of cubic NCs from an organic suspension into ordered cuboidal supraparticles (SPs) and their structural and optical properties. Upon increasing the NC concentration or by addition of a nonsolvent, the formation of the SPs occurs homogeneously in the suspension, as monitored by in situ X-ray scattering measurements. The three-dimensional structure of the SPs was resolved through high-angle annular dark-field scanning transmission electron microscopy and electron tomography. The NCs are atomically aligned but not connected. We characterize NC vacancies on superlattice positions both in the bulk and on the surface of the SPs. The occurrence of localized atomic-type NC vacancies—instead of delocalized ones—indicates that NC–NC attractions are important in the assembly, as we verify with Monte Carlo simulations. Even when assembled in SPs, the NCs show bright emission, with a red shift of about 30 meV compared to NCs in suspension.

Revealing a Vacancy Analog of the Crowdion Interstitial in Simple Cubic Crystals

“…Moreover, this mechanism also explains why such defects have not been observed more frequently: in attractive systems, which are more commonly found in nature, the attractions can both increase the barrier and remove the repulsions necessary to have the particles spread along the rows. Indeed, attractive interactions have been demonstrated to strongly suppress vacancy delocalization in simple cubic crystals of cubic nanoparticles [44]. Hence, the attractions in such systems need to be tuned to be weak in order to observe delocalized vacancies [35].…”

Highly Stable Perovskite Supercrystals via Oil-in-Oil Templating

“…Microscale supercubes have been obtained by slow drying of drop-casted CsPbBr 3 NCs. 15 The resulting ordered superstructures showed superfluorescence such as accelerated radiative decay, photon bunching, and delayed emission pulses at high excitation density. However, all these efforts remain small scale and of rather poor external control in terms of size, morphology, and crystal quality of the superstructures, leaving the controlled large-scale assembly for applications a major challenge.…”

“…Recently, inorganic perovskite NCs have emerged as a promising material for photovoltaic films, 14 exhibiting excellent optoelectronic properties and featuring bandgap tunability by size and composition, 15 energy transfer, 16 and carrier multiplication capabilities. 17 Yet, currently, only a few works have reported SCs made from perovskite NCs.…”

“… 15 (2) The volume ratio between the NC’s solvent and the solvent applied for treatment should be precisely controlled to obtain a specific morphology. 15 (3) Pretreatments of NCs sometimes are necessary to make them more hydrophilic to the substrates. 2 (4) Irregular morphology exists as well as individual NCs or bulklike impurities in the supercrystals.…”

“…These results are in stark contrast to the rather rapid decay of morphology and PL reported previously for perovskite cuboidal superstructures, which merged into single nanoplatelets within two weeks. 15 We hypothesize that the FC-40 oil plays a crucial role, being an inert oil resistant to high-temperature degradation. After the complete drying of the toluene phase, the resulting SCs are stabilized by the 008-FS, hindering ligand detachment, as the ligands are insoluble in the fluorinated oil, and avoiding further degradation and merging.…”