Experimental Evidence for Defect Tolerance in Pb-Halide Perovskites

The term defect tolerance (DT) is used often to rationalize the exceptional optoelectronic properties of Halide Perovskites, HaPs, and their devices. Even though DT lacked direct experimental evidence, it became fact in the field. DT in semiconductors implies tolerance to structural defects without the electrical and optical effects (e.g., traps), associated with such defects. We present first direct experimental evidence for DT in Pb HaPs by comparing the structural quality of 2D, 2D_3D, and 3D Pb HaP crystals with their optoelectronic characteristics using high sensitivity methods. Importantly, we get information from the material bulk, because we sample at least a few 100 nm, up to several micrometer, from the sample surface, which allows assessing intrinsic bulk (and not only surface) properties of HaPs. The results point to DT in 3D, to a lesser extent in 2D_3D, but not in 2D Pb HaPs. We ascribe such dimension dependent DT to the higher number of (near)neighboring species, available to compensate for structural defect effects in the 3D than in the 2D HaP crystals. Overall, our data provide an experimental basis to rationalize DT in Pb HaPs. These experiments and findings can guide the search for, and design of other materials with DT

Cell refinement of CsPbBr3 perovskite nanoparticles and thin films

In this work, we performed a detailed study of the phase transformations and structural unit cell parameters of CsPbBr3 nanoparticles (NPs) and thin films. In situ X-ray diffraction patterns were acquired as a function of temperature, where the positions and widths of the diffraction peaks were systematically tracked upon heating and cooling down to room temperature (RT). Scanning electron microscopy provides physical insight on the CsPbBr3 thin films upon annealing and transmission electron microscopy gives physical and crystallographic information for the CsPbBr3 NPs using electron diffraction. The secondary phase(s) CsPb2Br5 (and CsPb4Br6) are clearly observed in the XRD patterns of both nanoparticles and thin films upon heating to 500 K, whilst from 500 K to 595 K, these phases remain in small amounts and are kept like this upon cooling down to RT. However, in the case of thin films, the CsPb2Br5 secondary phase disappears completely above 580 K and pure cubic CsPbBr3 is observed up to 623 K. The CsPbBr3 phase is then kept upon cooling down to RT, achieving pure CsPbBr3 phase. This study provides detailed understanding of the phase behavior vs. temperature of CsPbBr3 NPs and thin films, which opens the way to pure CsPbBr3 phase, an interesting material for optoelectronic applications

Enhancing Stability and Photostability of CsPbI3 by Reducing Its Dimensionality

Full inorganic perovskites display their potential to function as stable photovoltaic materials better than the hybrid organic–inorganic perovskites. However, to date, the cesium lead iodide perovskite, which displays a promising absorbance range, has suffered from low stability, which degrades to a nonactive photovoltaic phase rapidly. In this work, we show that the black phase of cesium lead iodide can be stabilized when the perovskite dimensionality is reduced. X-ray diffraction, absorbance, and scanning electron microscopy were used to follow the degradation process of various dimensionalities under room conditions and 1 sun illumination. When comparing the effect on the stability and photostability of cesium lead iodide with linear or aromatic barrier molecules, the aromatic barrier molecule displays better photostability for over 700 h without degradation under continuous 1 sun illumination than does the linear barrier molecule. Theoretical calculations show that the addition of the barrier molecule makes a different charge distribution over the perovskite structure, which stabilizes the CsPbI3 black phase. This work provides the possibility to use the CsPbI3 perovskite as a stable photovoltaic material in solar cells

perovskite single crystals by alkylammonium post‐treatment

Abstract The zero‐dimensional Cs4PbBr6 perovskites are highly emissive materials that demonstrated an effective potential in light emitting applications. There is an on‐going debate regarding the origin of its strong and green photoluminescence, which is not in line with the expectedly wide band‐gap energy of the strongly confined material. Herein, using mortar and pestle, we react Cs4PbBr6 single crystals with methanol solutions of ammonium barrier molecules, and affect their optical and compositional properties. The ammonium barrier molecules react with the 0D Cs4PbBr6 crystals, and lead to a structural transformation of the CsPbBr3 inclusions into two‐dimensional perovskite within the 0D phase of the Cs4PbBr6. In addition, the photoluminescence quantum yield was increased as a result of the post treatment. This can explain the origin of the strong, green photoluminescence from these crystals. This novel post‐treatment affects the properties of the CsPbBr3 inclusions in Cs4PbBr6 crystals by a straightforward process, which can be utilized to another 0D perovskite

S-S bonds are not required for the sonochemical formation of proteinaceous microspheres: the case of streptavidin.

Proteinaceous microspheres can be prepared using the sonochemical method. However, it is known that these proteins should possess at least one cysteine residue in order to obtain stable microspheres using this method. In the present study, we have produced streptavidin microspheres, using the sonochemical method, from streptavidin, which does not have any cysteine residues

Two Dimensional Organometal Halide Perovskite Nanorods with Tunable Optical Properties

Organo-metal halide perovskite is an efficient light harvester in photovoltaic solar cells. Organometal halide perovskite is used mainly in its “bulk” form in the solar cell. Confined perovskite nanostructures could be a promising candidate for efficient optoelectronic devices, taking advantage of the superior bulk properties of organo-metal halide perovskite, as well as the nanoscale properties. In this paper, we present facile low-temperature synthesis of two-dimensional (2D) lead halide perovskite nanorods (NRs). These NRs show a shift to higher energies in the absorbance and in the photoluminescence compared to the bulk material, which supports their 2D structure. X-ray diffraction (XRD) analysis of the NRs demonstrates their 2D nature combined with the tetragonal 3D perovskite structure. In addition, by alternating the halide composition, we were able to tune the optical properties of the NRs. Fast Fourier transform, and electron diffraction show the tetragonal structure of these NRs. By varying the ligands ratio (e.g., octylammonium to oleic acid) in the synthesis, we were able to provide the formation mechanism of these novel 2D perovskite NRs. The 2D perovskite NRs are promising candidates for a variety of optoelectronic applications, such as light-emitting diodes, lasing, solar cells, and sensors