Strong violet emission from ultra-stable strontium-doped CsPbCl3 superlattices.

Among the lead halide perovskites, the photoluminescence quantum yields (PLQYs) of perovskite quantum dots (PQDs) in the violet region are the very lowest. This is an obstacle to the optical applications across the entire visible area based on perovskite materials. Herein, we report a novel strontium (Sr)-substitution along with chlorine passivation strategy to enhance the PLQYs of CsPbCl3 PQDs. We surprisingly found that when the molar ratio of Sr2+/Pb2+ = 0.1/0.9, CsSr0.1Pb0.9Cl3 PQDs exhibit strong single-color violet emission, which is attributed to the effective passivation of chlorine defects. We further found spontaneous self-assembly of PQDs into highly emissive PSCs from the precursor in a highly concentrated solution. Moreover, by dilution of these PSCs, a few small PQD aggregates can be regained, which is similar to the PQDs formed at lower concentrations. Benefiting from the superior collective properties of individual PQDs, these highly fluorescent CsSr0.1Pb0.9Cl3 PSCs can maintain good stability even when directly immersed in water or exposed to illumination.

Trioctylphosphine-Assisted Pre-protection Low-Temperature Solvothermal Synthesis of Highly Stable CsPbBr3/TiO2 Nanocomposites.

Lead halide perovskite quantum dots (PQDs) are reported as a promising branch of perovskites, which have recently emerged as a field in luminescent materials research. However, before the practical applications of PQDs can be realized, the problem of poor stability has not yet been solved. Herein, we propose a trioctylphosphine (TOP)-assisted pre-protection low-temperature solvothermal synthesis of highly stable CsPbBr3/TiO2 nanocomposites. Due to the protection of branched ligands and the lower temperature of shell formation, these TOP-modified CsPbBr3 PQDs are successfully incorporated into a TiO2 monolith without a loss of fluorescence intensity. Because the excellent nature of both parent materials is preserved in CsPbBr3/TiO2 nanocomposites, it is found that the as-prepared CsPbBr3/TiO2 nanocomposites not only display excellent photocatalytic activity but also yield improved PL stability, enabling us to build highly stable white light-emitting diodes and to photodegrade rhodamine B.

A versatile approach for shape-controlled synthesis of ultrathin perovskite nanostructures.

Very recently, ultrathin perovskite nanostructures, with the advantages of perovskite and ultrathin properties, have received an enormous level of interest due to their many fascinating properties, such as a strong quantum confinement effect and a large specific surface area. In spite of this incredible success of perovskite nanocrystals (NCs), the development of perovskite NCs is still in its infancy, and the production of high-quality ultrathin perovskite nanostructures has been a hot topic in the fields of nanoscience and nanotechnology. Herein, we demonstrate that ultrathin CsPbBr3 perovskite nanosheets (NSs) can be obtained by a simple mixing of precursor-ligand complexes under ambient conditions. It was found that the formation of NSs is ascribed to the stepwise self-assembly of the initially formed different types of ultrathin nanostructures. Due to the disappearance of grain boundaries and protection of branched ligands, these NSs exhibit enhanced optical properties compared to other types of samples. This direct synthesis method opens up a promising road for the synthesis of ultrathin NSs and guides the fabrication of other ultrathin nanostructures.

Revealing Energy Loss and Nonradiative Recombination Pathway in Mixed-Ion Perovskite Solar Cells.

Multiple-cation lead mixed-halide perovskites (MLMPs) with tunable band gaps have been demonstrated as ideal candidates to achieve perovskite solar cells with high efficiencies. It is well-known that a large open-circuit voltage (VOC) loss caused by nonradiative recombination still limits the approach to the Shockley-Queisser limit. However, there are few comprehensive contributions regarding the origin and pathway of nonradiative recombination in n-i-p structured MLMPs. Here, we compare the performance of MLMPs containing different halides and analyze the energy loss and interface trap-assisted nonradiative recombination characterizations. It is found that Br-containing devices with a lower interface trap density of 3.2 × 1013 cm-2 obtain a high VOC of 1.12 V, a small energy loss of 0.02 eV, radiative recombination current density of 8.05 × 10-21 A m-2, and total recombination current density of 22.16 mA cm-2. This work provides an opportunity to understand the device physics and reveals the nature of nonradiative recombination based on experiment and simulation.