Structure and Surface Passivation of Ultrathin Cesium Lead Halide Nanoplatelets Revealed by Multilayer Diffraction

Abstract

The research on two-dimensional colloidal semiconductors has received a boost from the emergence of ultrathin lead halide perovskite nanoplatelets. While the optical properties of these materials have been widely investigated, their accurate structural and compositional characterization is still challenging. Here, we exploited the natural tendency of the platelets to stack into highly ordered films, which can be treated as single crystals made of alternating layers of organic ligands and inorganic nanoplatelets, to investigate their structure by multilayer diffraction. Using X-ray diffraction alone, this method allowed us to reveal the structure of ∼12 Å thick Cs–Pb–Br perovskite and ∼25 Å thick Cs–Pb–I–Cl Ruddlesden–Popper nanoplatelets by precisely measuring their thickness, stoichiometry, surface passivation type and coverage, as well as deviations from the crystal structures of the corresponding bulk materials. It is noteworthy that a single, readily available experimental technique, coupled with proper modeling, provides access to such detailed structural and compositional information.

Organic Sulfonium‐Stabilized High‐Efficiency Cesium or Methylammonium Lead Bromide Perovskite Nanocrystals

“…Quantitative XPS results (Table S2) reveal that the atomic ratio of Cs/Pb/Br/S is 14.3 : 22.7 : 58.2 : 4.8. The Br/Pb (2.6) and Cs/Pb (0.6) atomic ratio are lower than the stoichiometry ratio, which is attributed to the X‐ray‐induced Br desorption during the measurement [27] and the partial replacement of surface Cs ions by DAM cations, [2] respectively.…”

Assembly, Properties, and Application of Ordered Group II–VI and IV–VI Colloidal Semiconductor Nanoparticle Films

“…For instance, multilayer diffraction analysis has been applied to stacks of cesium lead halide nanoplatelets or PbSe nanoplatelets and nanocrystals and delivered information on nanoparticle distance, composition, surface passivation, and structural disorder. [308,309] Last, we discussed charge carrier migration and radiative recombination processes in semiconductor nanocrystal superlattices. Characterization methods with high temporal and spatial resolution such as transient absorption microscopy unravel charge migration processes on different timescales and complement methods such as THz spectroscopy and photoconductivity measurements.…”

“…For instance, multilayer diffraction analysis has been applied to stacks of cesium lead halide nanoplatelets or PbSe nanoplatelets and nanocrystals and delivered information on nanoparticle distance, composition, surface passivation, and structural disorder. [ 308,309 ]…”

Colloidal Metal‐Halide Perovskite Nanoplatelets: Thickness‐Controlled Synthesis, Properties, and Application in Light‐Emitting Diodes

“…[ 59 ] A recent study by Manna's group suggests that 2 ML thick NPls also adapt orthorhombic crystal structure. [ 104 ] Furthermore, it was proposed that the NPl surface terminates with CsBr with half of the Br and Cs positions vacant. [ 59 ] These vacancies can significantly hamper the optical properties of NPls, however, they can be repaired (or passivated) by different ways to recover their properties, as discussed in the following section.…”