Controlled synthesis of brightly fluorescent CH3NH3PbBr3perovskite nanocrystals employing Pb(C17H33COO)2as the sole lead source

Chemical synthesis and optical, structural, and surface characterization of InP-In2O3 quantum dots

InP-In₂O₃ colloidal quantum dots (QDs) synthesized by a single-step chemical method without injection of hot precursors (one-pot) were investigated. Specifically, the effect of the tris(trimethylsilyl)phosphine, P(TMS)₃, precursor concentration on the QDs properties was studied to effectively control the size and shape of the samples with a minimum size dispersion. The effect of the P(TMS)₃ precursor concentration on the optical, structural, chemical surface, and electronic properties of InP-In₂O₃ QDs is discussed. The absorption spectra of InP-In₂O₃ colloids, obtained by both UV-Vis spectrophotometry and photoacoustic spectroscopy, showed a red-shift in the high-energy regime as the concentration of the P(TMS)₃ increased. In addition, these results were used to determine the band-gap energy of the InP-In₂O₃ nanoparticles, which changed between 2.0 and 2.9 eV. This was confirmed by Photoluminescence spectroscopy, where a broad-band emission displayed from 2.0 to 2.9 eV is associated with the excitonic transition of the InP and In₂O₃ QDs. In₂O₃ and InP QDs with diameters ranging approximately from 8 to 10 nm and 6 to 9 nm were respectively found by HR-TEM. The formation of the InP and In₂O₃ phases was confirmed by X-ray Photoelectron Spectroscopy.

In situ inclusion of thiocyanate for highly luminescent and stable CH3NH3PbBr3 perovskite nanocrystals

In this work, an in situ thiocyanate inclusion method for the fabrication of highly luminescent and stable CH3NH3PbBr3 perovskite nanocrystals (NCs) is developed, employing Pb(SCN)2 as the lead precursor to partially or totally replace PbBr2 in the ligand-assisted reprecipitation (LARP) process. The in situ approach not only avoids the introduction of impurity elements, but also more interestingly incorporation of thiocyanate can control the crystallinity, particle size, luminescence and stability of CH3NH3PbBr3 NCs in a simple and effective manner. By adjusting the thiocyanate concentration, the photoluminescence (PL) of the synthesized CH3NH3PbBr3 NCs can be tuned in a range of 473-526 nm, as characterized by narrow emission line widths of 21-28 nm and outstanding photoluminescence quantum yields (PLQYs) of 73% to 96%. Meanwhile, the stability of CH3NH3PbBr3 NCs can be greatly improved as the amount of thiocyanate increases. The improvement in the optical performance and stability of CH3NH3PbBr3 NCs is mainly due to the contribution of higher crystallinity and, more stable and defect-free surface passivation induced by the presence of thiocyanate. This work paves a novel way for preparing highly luminescent and stable CH3NH3PbBr3 NCs.

Electronic Properties of Free-Standing Surfactant-Capped Lead Halide Perovskite Nanocrystals Isolated in Vacuo

We report an investigation of lead halide perovskite CH₃NH₃PbBr₃ nanocrystals and associated ligand molecules by combining several different state-of-the-art experimental techniques, including synchrotron radiation-based XPS and VUV PES of free-standing nanocrystals isolated in vacuum. By using this novel approach for perovskite materials, we could directly obtain complete band alignment to vacuum of both CH₃NH₃PbBr₃ nanocrystals and the ligands widely used in their preparation. We discuss the possible influence of the ligand molecules to apparent perovskite properties, and we compare the electronic properties of nanocrystals to those of bulk material. The experimental results were supported by DFT calculations.