Perovskite Core Research Articles

Highly Stable Photoluminescence in Vacuum‐Processed Halide Perovskite Core–Shell 1D Nanostructures

AbstractHybrid organometal halide perovskites (HP) present exceptional optoelectronic properties, but their poor long‐term stability is a major bottleneck for their commercialization. Herein, a solvent‐free approach to growing single‐crystal organic nanowires (ONW) is presented, along with nanoporous metal oxide scaffolds and HP, to form a core@multishell architecture. The synthesis is carried out under mild vacuum conditions employing thermal evaporation for the metal‐free phthalocyanine (H2Pc) nanowires, which are the core, plasma‐enhanced chemical vapor deposition (PECVD) for the TiO2 shell, and co‐evaporation of lead iodide (PbI2) and methylammonium iodide (CH3NH3I/MAI) for the CH3NH3PbI3 (MAPbI3/MAPI) perovskite shell. A detailed characterization of the nanostructures by electron microscopy, (S)‐TEM, and X‐ray diffraction, XRD, is presented, revealing a different crystallization of the HP depending on the template: while the growth on H2Pc nanowires induces the typical MAPI tetragonal structure, a low‐dimensional phase (LDP) is observed on the 1D‐TiO2 nanotubes. Such a combination yields an unprecedentedly stable photoluminescence emission over 20 h and over 300 h after encapsulation in polymethyl methacrylate (PMMA) under different atmospheres including N2, air, and high moisture levels. Moreover, the unique 1D morphology of the system, together with the high refractive index, allows for a strong waveguiding effect along the HP nanowire length.

Multishell Nanophotonic Particles with Perovskite Core for Ratiometric Biochemical Sensing and Imaging

Multishell Nanophotonic Particles with Perovskite Core for Ratiometric Biochemical Sensing and Imaging

Conjugated Zwitterionic Oligomers as Ligands on Perovskite Nanocrystals: Hybrid Structures with Tunable Interparticle Spacing.

Conventional ligands for CsPbBr3 perovskite nanocrystals (NCs), composed of polar, coordinating head groups (e.g., ammonium or zwitterionic) and aliphatic tails, are instrumental in stabilizing the NCs against sintering and aggregation. Nonetheless, the aliphatic (insulating) nature of these ligands represents drawbacks with respect to objectives in optoelectronics, and yet removing these ligands typically leads to a loss of colloidal stability. In this paper, we describe the preparation of CsPbBr3 NCs in the presence of discrete conjugated oligomers that were prepared by an iterative synthetic approach and capped at their chain ends with sulfobetaine zwitterions for perovskite coordination. Notably, these zwitterionic oligofluorenes are compatible with the hot injection and ligand exchange conditions used to prepare CsPbBr3 NCs, yielding stable NC dispersions with high photoluminescence quantum yields (PLQY, >90%) and spectral features representative of both the perovskite core and conjugated ligand shell. Controlling the chain length of these capping ligands effectively regulated inter-NC spacing and packing geometry when cast into solid films, with evidence derived from both transmission electron microscopy (TEM) and grazing incidence X-ray scattering measurements.

Few-mode metal-free perovskite optical fiber with second-order optical nonlinearity

Semiconductor core optical fibers are highly desirable for fiber-based photonic and optoelectronic applications as they can combine strong optical nonlinearities, tight light confinement, wide transmission bands, and electronic functionality within a single platform. Perovskites have emerged as particularly exciting materials for semiconductor photonics as they have strong optical nonlinearities and tunable optoelectronic bandgaps. However, lead-based perovskites contain toxic elements and are, therefore, not environmentally friendly. Furthermore, in fiber form, their core-size is prohibitively large, making them unsuitable for nonlinear optics and applications that require single-mode guidance, such as telecommunications. Here, we report a metal-free perovskite core optical fiber where lead has been substituted for an ammonium cation in the perovskite structure. The core material has a wide bandgap greater than 5 eV, a high laser damage threshold, and a core diameter that can be produced as small as 5 µm. At this core size, the fiber supports just six modes, and the fundamental mode can readily be excited and isolated. Moreover, the metal-free perovskite has a second-order susceptibility that is absent in the archetypal lead-based perovskites and many other semiconductor core materials, such as silicon and germanium. The second-order susceptibility is important for many nonlinear optics applications, such as second-harmonic generation and quantum optics.

Two-Dimensional Halide Pb-Perovskite-Double Perovskite Epitaxial Heterostructures.

Epitaxial heterostructures of two-dimensional (2D) halide perovskites offer a new platform for studying intriguing structural, optical, and electronic properties. However, difficulties with the stability of Pb- and Sn-based heterostructures have repeatedly slowed the progress. Recently, Pb-free halide double perovskites are gaining a lot of attention due to their superior stability and greater chemical diversity, but they have not been successfully incorporated into epitaxial heterostructures for further investigation. Here, we report epitaxial core-shell heterostructures via growing Pb-free double perovskites (involving combinations of Ag(I)-Bi(III), Ag-Sb, Ag-In, Na-Bi, Na-Sb, and Na-In) around Pb perovskite 2D crystals. Distinct from Pb-Pb and Pb-Sn perovskite heterostructures, growths of the Pb-free shell at 45° on the (100) surface of the lead perovskite core are observed in all Pb-free cases. The in-depth structural analysis carried out with electron diffraction unequivocally demonstrates the growth of the Pb-free shell along the [110] direction of the Pb perovskite, which is likely due to the relatively lower surface energy of the (110) surface. Furthermore, an investigation of anionic interdiffusion across heterostructure interfaces under the influence of heat was carried out. Interestingly, halide anion diffusion in the Pb-free 2D perovskites is found to be significantly suppressed as compared to Pb-based 2D perovskites. The great structural tunability and excellent stability of Pb-free perovskite heterostructures may find uses in electronic and optoelectronic devices in the near future.

Fast ion-conductive electrolyte based on a doped LaAlO3 with an amorphous surface layer for low-temperature solid oxide fuel cells

Ion transport in solid oxide electrolytes is a key process involved in advanced green energy conversion devices such as solid oxide fuel cells (SOFCs). Conventional SOFC electrolytes require a high operational temperature (over 700 °C) to maintain considerable bulk and grain boundary diffusion of the ions to enable sufficient ionic conductivity for efficient fuel cell operation. The present study explores a novel ion conduction expressway in an amorphous/crystalline heterostructure, La0·8Sr0·2Al0·8Zn0·2O3-δ (LSAZ), which can boost the mobility of ions at a relatively low temperature (450–550 °C) for SOFCs. The LSAZ heterostructure includes an insulating perovskite core and a superionic-conducting amorphous surface layer. This electrolyte exhibits a superior conductivity of 0.319 S cm−1 at 550 °C, and it is employed in a SOFC which demonstrates a remarkable performance of 1296 mW cm−2 at 550 °C, which is 300 times higher than a SOFC with the LSAZ being densified at 1400 °C for 10 h. A superionic conducting amorphous surface layer enriched by high oxygen vacancy defects facilitates ionic conduction along the grain boundary and interfaces between the nanoparticles of LSAZ. Our finding provides an efficient way to design advanced highly conductive electrolytes for solid oxide fuel cells to be operated at reduced temperatures.

Impact of core-shell perovskite nanocrystals for LED applications: successes, challenges, and prospects.

Perovskite nanocrystals (PeNCs) synthesized by colloidal solution methods are an outstanding case of study due to their remarkable optical features, different from their bulk counterpart, such as a tuneable band gap and narrower photoluminescence emission, altered by the size and shape. However, the stability of these systems needs to be improved to consolidate their application in optoelectronic devices. Improved PeNC quality is associated with a less defective structure, as it affects negatively the photoluminescence quantum yield (PLQY), due to the essential, but at the same time labile interaction between the colloidal capping ligands and the perovskite core. In this sense, it would be extremely effective to obtain an alternative method to stabilize the PeNC phases and passivate the surface, in order to improve both stability and optical properties. This objective can be reached exploiting the structural benefits of the interaction between the perovskite and other organic or inorganic materials with a compatible structure and optical properties and limiting the optical drawbacks. This perspective contemplates different combinations of core/shell PeNCs and the critical steps during the synthesis, including drawbacks and challenges based on their optical properties. Additionally, it provides insights for future light emitting diode (LED) applications and advanced characterization. Finally, the existing challenges and opportunities for core/shell PeNCs are discussed.

Enhanced crystal quality of perovskite via protonated graphitic carbon nitride added in carbon-based perovskite solar cells

The quality of perovskite layers has a great impact on the performance of perovskite solar cells (PSCs). However, defects and related trap sites are generated inevitably in the solutionprocessed polycrystalline perovskite films. It is meaningful to reduce and passivate the defect states by incorporating additive into the perovskite layer to improve perovskite crystallization. Here an environmental friendly 2D nanomaterial protonated graphitic carbon nitride (p-g-C3N4) was successfully synthesized and doped into perovskite layer of carbon-based PSCs. The addition of p-g-C3N4 into perovskite precursor solution not only adjusts nucleation and growth rate of methylammonium lead tri-iodide (MAPbI3) crystal for obtaining flat perovskite surface with larger grain size, but also reduces intrinsic defects of perovskite layer. It is found that the p-g-C3N4 locates at the perovskite core, and the active groups -NH2/NH3 and NH have a hydrogen bond strengthening, which effectively passivates electron traps and enhances the crystal quality of perovskite. As a result, a higher power conversion efficiency of 6.61% is achieved, compared with that doped with g-C3N4 (5.93%) and undoped one (4.48%). This work demonstrates a simple method to modify the perovskite film by doping new modified additives and develops a low-cost preparation for carbon-based PSCs.

Amphiphilic Polymer Ligand-Assisted Synthesis of Highly Luminescent and Stable Perovskite Nanocrystals for Sweat Fluorescent Sensing.

The weak interfacial binding affinities of the inorganic perovskite core with ligands and high density of surface defect states induce the facile detachment of surface ligands from nanocrystals (NCs), resulting in their poor colloidal stability and fluorescence in aqueous. In this work, a powerful ligand engineering strategy was proposed for eliminating the surface defects and aggregation of the NCs. Using an amphiphilic polymer octylamine-modified polyacrylic acid (OPA) as a capping ligand, the as-synthesized CsPbBr3 NCs retain high photoluminescence intensity and stability by the modified ligand-assisted reprecipitation method. The increase in the fluorescence lifetime and NC size could also be observed, and how the NC particle size influences fluorescence lifetime was further studied. In addition, the water stability, photostability, and thermal stability were significantly improved, and the fluorescence of NCs can maintain 80.13% of the original value in water for 15 d. We further validated that the strong binding affinity of OPA and oleylamine ligands with CsPbBr3 NCs leads to a reduction in surface trap states, and a large amount of carboxyl groups of the OPA made the NCs preserve good water solubility. In addition, the OPA has the ability of adjusting the particle size of NCs. Furthermore, a wavelength-shifted colorimetric sensor based on these NCs was constructed for detection of Cl- in sweat, which enables the rapid and visual detection of Cl- with high accuracy and stability. Overall, these CsPbBr3 NCs synthesized by the ligand engineering strategy validated their wide applications in biomedical sensing fields.

Luminescence and Stability Enhancement of Inorganic Perovskite Nanocrystals via Selective Surface Ligand Binding.

Colloidal lead halide perovskite nanocrystals (NCs) have recently emerged as one of the most promising light-emitting materials for optoelectronic devices with outstanding performance. However, the facile detachment of surface capping organic ligands from these NCs leads to very poor colloidal stability and durability. This is mainly due to the weak interfacial interactions between the inorganic perovskite core and ligands, high density of surface defect states, and aggregation of NCs. Here, using a combination of time-resolved laser spectroscopy and density functional theory (DFT) calculations, we explored the major impact of surface orientations and terminations for both CsPbBr3 and Cs4PbBr6 NCs not only on the interfacial binding affinities with organic ligands but also on surface defect formation and NC aggregation. By rationalizing that surface trap states are responsible for the decrease in photoluminescence (PL) upon fabrication and purification, we propose a powerful ligand-engineering strategy for eliminating these trap states and preventing the aggregation of CsPbBr3 and Cs4PbBr6 NCs. Interestingly, we find that the surface orientation and dimensionality determine the degree of interfacial interactions between the inorganic perovskite core and ligands and subsequently control the overall PL intensity and NC stability. Our results demonstrate that a treatment of as-synthesized CsPbBr3 NCs consisting of the addition of extra oleylammonium bromide (OAmBr) as a capping ligand, allows the CsPbBr3 NCs to retain their green emission with increased PL intensity and quantum yields and improves colloidal durability. On the other hand, the ultraviolet emissions of Cs4PbBr6 NCs are effectively increased upon addition of extra cesium oleate (CsOL) as the trap states induced by surface cesium ions are largely reduced by the formation of Cs-O bonds. Our work provides a robust and adequate ligand engineering approach to significantly enhance the optical behavior of perovskite NCs with different dimensionalities and various compositions and to achieve more efficient and stable light-harvesting devices.

One-step formation of core/shell structure based on hydrophobic silane ligands for enhanced luminescent perovskite quantum dots

Organometal halide perovskite (MAPbX3; MA = CH3NH3, X = Br, I) quantum dots (QDs) have attracted significant interest as color-adjustable and high-purity light-emitting materials for lighting and display applications. However, the photoluminescence (PL) intensity and lifetime of the organometal halide perovskites are negatively affected by their polarity and poor thermal stability. Here, to improve these issues, the synthesis of hydrophobic MAPbBr3 QDs@SiO2 core/shell structures through a split-ligand mediated re-precipitation (S-LMRP) method is presented. This is done through one-pot process without ligand exchange treatment after QDs synthesis. In this synthesis, 3-aminopropyl(diethoxy)methylsilane (APDEMS) is used as the silica precursor to obtain a hydrophobic surface with CH3 groups. Therefore, core/shell QDs synthesized using APDEMS are hydrophobic, which induce superior dispersibility. This also have good stability in polar solvents as well as thermal and photo environments, unlike the bare-QDs. This has the advantage of not only protecting the perovskite core due to the shell, but also suppressing the release of heavy metals. Moreover, it has a relatively narrow full width at half-maximum and a PL quantum yield of 96.5%. Turbiscan measurements demonstrated better dispersibility in the newly designed core/shell QD compared to the conventional QD (agglomerated in suspension). Finally, this proposed method enable is applicable to the preparation of not only green but also red and blue light-emitting core/shell QDs, which is expected to have an attractive impact for display applications.

Deciphering the excited-state dynamics and multicarrier interactions in perovskite core-shell type hetero-nanocrystals.

Deciphering and modulating the carrier dynamics of perovskite nanocrystals (Pe-NCs) is crucial for their optoelectronic applications, which remains elusive to date. Herein, we, for the first time, explore the ultrafast dynamics of perovskite core-shell type NCs using CsPbBr3@ZnS as a model system. According to the transient spectroscopic characterization, a physical picture of the ultrafast dynamics in core-shell Pe-NCs is built. Specifically, we directly observed the "hot" hole transfer from CsPbBr3 to ZnS and confirmed the formation of charge-transfer state in CsPbBr3@ZnS NCs. Such ultrafast (<100 fs) hole rearrangement speeds up the carrier cooling and breaks the hot phonon bottleneck effect in Pe-NCs. Moreover, thanks to the charge separation in CsPbBr3@ZnS NCs, the Auger recombination is largely suppressed and the Auger lifetime is increased nearly 5-fold compared to that of "pure" CsPbBr3 NCs, which endows CsPbBr3@ZnS NCs with unique optical gain properties. These results are informative for halide perovskite-based applications, such as photocatalysis, hot-carrier photovoltaics and lasers.

Perovskite Core-Shell Nanowire Transistors: Interfacial Transfer Doping and Surface Passivation.

While halide perovskite electronics are rapidly developing, they are greatly limited by the inferior charge transport and poor stability. In this work, effective surface charge transfer doping of vapor-liquid-solid (VLS)-grown single-crystalline cesium lead bromide perovskite (CsPbBr3) nanowires (NWs) via molybdenum trioxide (MoO3) surface functionalization is achieved. Once fabricated into NW devices, due to the efficient interfacial charge transfer and reduced impurity scattering, a 15× increase in the field-effect hole mobility (μh) from 1.5 to 23.3 cm2/(V s) is accomplished after depositing the 10 nm thick MoO3 shell. This enhanced mobility is already better than any mobility value reported for perovskite field-effect transistors (FETs) to date. The photodetection performance of these CsPbBr3/MoO3 core-shell NWs is also investigated to yield a superior responsivity (R) up to 2.36 × 103 A/W and an external quantum efficiency (EQE) of over 5.48 × 105% toward the 532 nm regime. Importantly, the MoO3 shell can provide excellent surface passivation to the CsPbBr3 NW core that minimizes the diffusion of detrimental water and oxygen molecules, improving the air stability of CsPbBr3/MoO3 core-shell NW devices. All these findings evidently demonstrate the surface doping as an enabling technology to realize high-mobility and air-stable low-dimensional halide perovskite devices.

A novel core-shell LSCF perovskite structured electrocatalyst with local hetero-interface for solid oxide fuel cells

In this work, a La0.6Sr0.4Co0.2Fe0.8O3-δ (LSCF113) perovskite core coated by Ruddlesden-Popper phase La0.6Sr1.4Co0.2Fe0.8O4-δ (LSCF214) thin film to form a LSCF113-214 core-shell structure cathode is synthesized by Sr2+ solution coating method. Its phase composition, lattice structure, electrochemical catalytic activity and full cell performance are investigated. The electrocatalytic activity and stability of the LSCF113 cathode are enhanced by in situ formation of LSCF214 on the LSCF113 surface. The electrochemical performance enhancement is due to the higher catalytic activity of the LSCF214 Ruddlesden-Popper phase and the mismatch of the lattice parameters between the LSCF214 and LSCF113 regions leading to more favorable oxygen vacancy formation and oxygen molecule adsorption. The electrochemical impedance spectrum indicates that LSCF113-214 electrode has a lower polarization resistance (0.17 Ωcm2) than the LSCF113 electrode (0.32 Ωcm2) at 650 °C. And the long term stability of LSCF113-214 is evaluated with no structure evolution in 400 h test at 600 °C. An anode-supported single cell with doped ceria as the electrolyte is used to evaluate the electrochemical performance of LSCF113-214, which shows an open circuit voltage of 0.81 V and a maximum power density of 0.57 W cm−2 at 650 °C.

Cyclic Peptide Stabilized Lead Halide Perovskite Nanoparticles

Combining the unique properties of peptides as versatile tools for nano- and biotechnology with lead halide perovskite nanoparticles can bring exceptional opportunities for the development of optoelectronics, photonics, and bioelectronics. As a first step towards this challenge sub 10 nm methylammonium lead bromide perovskite colloidal nanoparticles have been synthetizes using commercial cyclic peptide Cyclo(RGDFK), containing 5 amino acids, as a surface stabilizer. Perovskite nanoparticles passivated with Cyclo(RGDFK) possess charge transfer from the perovskite core to the peptide shell, resulting in lower photoluminescence quantum yields, which however opens a path for the application where charge transfer is favorable.

Nitrate Ion-Incorporated Stable Perovskite Nanocrystals by a Solvent-Free Mechanochemical Reaction.

We have synthesized a new class of organolead halide perovskite nanocrystals by a solvent-free mechanochemical green approach. We have developed a new combination of precursor by incorporating nitrate ions into the MAPbBr3 perovskite core. While the presence of nitrate ion is evidenced by Fourier-transform infrared spectra, X-ray diffraction data shows the formation of perovskite nanocrystals. By altering the precursor composition, the morphology of the nanocrystals changes. Photoluminescence properties of these nanocrystals are preserved. Moreover, the stability of these nanocrystals is monitored for a long time, which shows that the incorporation of nitrate ions into the perovskite nanocrystal core does not have any decremental effect on its stability. Nonetheless, this strategy to synthesize perovskite nanocrystals reduces the solvent toxicity.

(Invited) Synthesis of Ultrastable Hairy Perovskite and Plasmonic Core/Shell Nanoparticles for Perovskite Solar Cells

We develop a viable strategy to create uniform ultrastable perovskite/metal oxide core/shell nanoparticles with good control over the dimension by capitalizing on amphiphilic star-like triblock copolymers as templates. The diameter of the perovskite core and the thickness of the metal oxide shell can be independently and precisely regulated by tailoring the molecular weights (i.e., the lengths) of the inner and intermediate blocks of star-like triblock copolymers, respectively. The successful synthesis of perovskite/metal oxide core/shell nanoparticles is confirmed by a suite of characterizations. Moreover, metal/metal oxide core/shell nanoparticles are also synthesized using amphiphilic star-like triblock copolymer templates. The resulting perovskite/metal oxide nanoparticles exhibit the remarkable compositional, thermal, moisture stabilities. These perovskite/metal oxide and metal/metal oxide nanoparticles are then used in perovskite solar cells, with which improved device performance is observed.

An efficient synthetic strategy for uniform perovskite core–shell nanocubes NaMgF3:Mn2+,Yb3+@NaMgF3:Yb3+ with enhanced near infrared upconversion luminescence

Uniform perovskite core–shell nanocubes NaMn1−xMgxF3@NaMgF3 and NaMn1−xMgxF3:Yb3+@NaMgF3:Yb3+ have been successfully synthesized via a facile one-pot co-precipitation method at room temperature.

Novel core–shell structure of perovskite anode and characterization

The core–shell anode particulates are prepared with perovskite core of (Sr0.7La0.3)(Ti1−xNbx)O3 and the shell of multiple elements doped solid electrolyte (La0.75Sr0.2Ba0.05)0.175Ce0.825O1.891 (LSBC) by a citric acid-based combustion (SV) coating process. The ionic shell LSBC precedes the peak reduction–oxidation reaction temperature of the anode to 500 °C. The selected coverage ratio of 1.5 or 3.0 mol% LSBC shell on the core is used to ensure appropriate electrocatalytic activity and electronic conductivity. The core–shell anode increases the interface charge transfer (ReZ(i)) and chemical catalysis (ReZ(c)) that is revealed on the reduction of AC impedance. The lower slope of the voltage drop for the half-cell, which is composed of the core–shell anode, indicates the increasing effective triple phase boundary (TPB) sites and reduces the interface thermal expansion and lattice matching, as well as extends the ionic conduction path from LSBC electrolyte to the core–shell anode. The power density increases three times by using the core–shell structural anode than without using the core–shell anode in the half-cell.