Dimethylammonium iodide stabilized bismuth halide perovskite photocatalyst for hydrogen evolution

Metal halide perovskites have emerged as novel and promising photocatalysts for hydrogen generation.Currently,their stability in water is a vital and urgent research question.In this paper a novel approach to stabilize a bismuth halide perovskite[(CH₃)₂NH₂]₃[Bil₆](DA₃Bil₆)in water using dimethylammonium iodide(DAI)without the assistance of acids or coatings is reported.The DA3Bil6 powder exhibits good stability in DAI solutions for at least two weeks.The concentration of DAI is found as a critical parameter,where the I^-ions play the key role in the stabilization.The stability of DA3Bil6 in water is realized via a surface dissolution-recrystallization process.Stabilized DA3Bil6 demonstrates constant photocatalytic properties for visible light-induced photo-oxidation of I^-ions and with PtCI4 as a co-catalyst(Pt-DA₃Bil₆),photocatalytic H2 evolution with a rate of 5.7μmol·h^-1from HI in DAI solution,obtaining an apparent quantum efficiency of 0.83%at 535 nm.This study provides new insights on the stabilization of metal halide perovskites for photocatalysis in aqueous solution.     

Aligned nanowires and nanodots by directed block copolymer assembly

The directed self-assembly of block copolymers (BCPs) is a promising route to generate highly ordered arrays of sub-10 nm features. Ultradense arrays of a monolayer of spherical microdomains or cylindrical microdomains oriented parallel to the surface have been produced where the lateral ordering is guided by surface patterning and the lattice defined by the patterning can be commensurate or incommensurate with the natural period of the BCP. Commensurability between the two can be used to elegantly manipulate the lateral ordering and orientation of the BCP microdomains so as to form well-aligned arrays of 1D nanowires or 2D addressable nanodots. No modification of the substrate surface, aside from the patterning, was used, making the influence of lattice mismatch and pattern amplification on the size, shape and pitch of the BCP microdomains more transparent. A skew angle between incommensurate lattices, defining a stretching or compression of the BCP chains to compensate for the lattice mismatch, is presented.     

A liquid phase anion-exchange approach to high-quality all-inorganic halide perovskite micro- and nanowires

All-inorganic halide perovskite nanowires (NWs) are promising materials due to they have broad application prospects in the field of optoelectronics, with mixed-halide perovskite nanowires can change the optoelectronic properties by adjusting the halide ratio. Here, we experimentally investigated the two-process governed anion-exchange reaction in single-crystalline CsPbX₃ micro- and nanowires. The critical parameters affecting the outcome of the reaction are identified as the reaction temperature, reaction time, and precursor concentrations. Upon examining the photoluminescence and morphology of the NWs, high-quality NWs were obtained by optimizing these critical parameters. The bandgap of the NWs can be tuned over the entire visible spectra (430–700 nm). In addition, photodetectors incorporating single NWs were fabricated, which demonstrated excellent responsivity under illumination. Our results expand the validity of liquid-phase anion exchange to the microscale, and lay the basis for liquid-processed optoelectronics and displays.

     

Confinement of elastomeric block copolymers via forced assembly coextrusion

Forced assembly processing provides a unique opportunity to examine the effects of confinement on block copolymers (BCPs) via conventional melt processing techniques. The microlayering process was utilized to produce novel materials with enhanced mechanical properties through selective manipulation of layer thickness. Multilayer films consisting of an elastomeric, symmetric block copolymer confined between rigid polystyrene (PS) layers were produced with layer thicknesses ranging from 100 to 600 nm. Deformation studies of the confined BCP showed an increase in ductility as the layer thickness decreased to 190 nm due to a shift in the mode of deformation from crazing to shear yielding. Postextrusion annealing was performed on the multilayer films to investigate the impact of a highly ordered morphology on the mechanical properties. The annealed multilayer films exhibited increased toughness with decreasing layer thickness and resulted in homogeneous deformation compared to the as-extruded films. Multilayer coextrusion proved to be an advantageous method for producing continuous films with tunable mechanical response.     

Hierarchical assembly of nanostructured organosilicate networks via stereocomplexation of block copolymers

The effect of the stereochemistry of polylactide (PLA)-based block copolymers on templated inorganic nanostructures has been investigated from the self-assembly of a stereoisomer pair/organosilicate mixture followed by organosilicate vitrification and copolymer thermolysis. Isomeric PLA homopolymers, block copolymers, and a stereoblock copolymer were prepared by ring-opening polymerization of D-, L-, or rac-lactide using an organocatalytic catalyst. Both differential scanning calorimetry and atomic force microscopy showed the formation of a stereocomplex between enantiomeric stereoisomers, that is, block copolymer/block copolymer and block copolymer/homopolymer mixtures as well as a stereoblock copolymer. The unique noncovalent interactions driven by stereocomplexation of D- and L-lactide provided supramolecular structures with a hierarchical order as characterized by distinctive vertical and horizontal growth of toroidal nanostructured inorganic features. This study demonstrates the potential of hierarchically assembling suprastructures that bridge the nano- to mesoscale feature sizes in the design of tunable functional nanomaterials suitable for future applications of microelectronics, material science, and bioengineering.     

Graphoepitaxial assembly of asymmetric ternary blends of block copolymers and homopolymers

Ternary blends of cylinder-forming polystyrene-block-poly(methyl methacrylate) block copolymers and polystyrene and poly(methyl methacrylate) homopolymers were assembled in trench features of constant width. Increasing the fraction of homopolymer in the blend increased the spacing and size of block copolymer domains, which were oriented perpendicular to the substrate to form a hexagonal lattice within the trench. The number of rows of cylinders within the trench was controlled by the blend composition. Depending on the domain size and spacing, the hexagonal lattice was stretched or compressed perpendicular to the trench walls but not perturbed parallel to the walls, indicating a decoupling of the perturbation in the perpendicular and parallel directions. The row spacing was uniform across the trench as a function of position from the trench wall. The results are compared with an analytical model and with Monte Carlo simulations.     

铅卤钙钛矿太阳能电池界面工程的近期进展

铅卤钙钛矿太阳能电池因其优良的光电转换效率以及相对低廉的制备成本而受到广泛关注。然而铅卤钙钛矿太阳能电池的长期稳定性限制了其商业化的进程。界面非辐射复合导致铅卤钙钛矿太阳能电池产生能量损失、影响器件稳定性,是造成器件性能恶化的主要原因。界面工程作为一种有效的策略被用于抑制界面非辐射复合,在制备高效稳定的铅卤钙钛矿太阳能电池方面取得了切实的成效。本文阐述了铅卤钙钛矿太阳能电池的工作原理以及界面上的非辐射复合过程,分析了界面非辐射复合产生的原因,总结了近期n-i-p正式结构铅卤钙钛矿太阳能电池中界面工程的研究进展,讨论了其作用机制。基于目前铅卤钙钛矿太阳能电池中的界面工程发展现状,对其未来的发展方向进行了展望。     

Broadband and sensitive two-dimensional halide perovskite photodetector for full-spectrum underwater optical communication

Full-spectrum underwater optical communication(UOC)is of great significance for major strategic needs including resource development,scientific exploration,and homeland security.As the core of the full-spectrum UOC system,photodetectors(PDs)are plagued by stringent requirements including a broadband response,intrinsic water resistance,and a high detectivity.In this work,two-dimensional(2D)halide perovskites(HPs)and corresponding PDs are constructed by stearamine(SA),representing the rarely explored long-chain aliphatic amine series,to own waterproofness,ultralow noise,and superior optoelectronic performance,which consequently enable a high suitability for UOC.By dimensionality and composition modulations to extend the absorption onset down to 1.5 eV,a broadband response covering the entire transmission window of water(>1.55 eV)for full-spectrum UOC can be obtained.Besides,featuring a high responsivity of 3.27 A·W^-1,a peak external quantum efficiency(EQE)of 630%,fast rise/decay times of 0.35 ms/0.54 ms,a superior detectivity up to 1.35×10¹²Jones and the capability to distinguish various waveforms and light intensities,the PDs present sensitive and persistent photoresponse underwater.As a result,proof-of-concept wireless transmission of ASCII codes in water is demonstrated.     

Optical management for efficiency enhancement in hybrid organic-inorganic lead halide perovskite solar cells

In a few years only, solar cells using hybrid organic–inorganic lead halide perovskites as optical absorber have reached record photovoltaic energy conversion efficiencies above 20%. To reach and overcome such values, it is required to tailor both the electrical and optical properties of the device. For a given efficient device, optical optimization overtakes electrical one. Here, we provide a synthetic review of recent works reporting or proposing so-called optical management approaches for improving the efficiency of perovskite solar cells, including the use of anti-reflection coatings at the front substrate surface, the design of optical cavities integrated within the device, the incorporation of plasmonic or dielectric nanostructures into the different layers of the device and the structuration of its internal interfaces. We finally give as outlooks some insights into the less-explored management of the perovskite fluorescence and its potential for enhancing the cell efficiency.     

嵌段共聚物合成方法研究进展

综述了近年来聚烯烃嵌段共聚物多种合成方法,包括:活性聚合方法(阴离子、阳离子活性聚合,基团转移聚合,自由基活性聚合,配位活性聚合)、正离子聚合转化法、力化学方法、缩聚法和特殊引发剂法等。同时讨论了各种合成方法的优点及局限性,探讨了其在工业应用上的重要意义。     

Nanostructure engineering by templated self-assembly of block copolymers

Self-assembling materials are the building blocks for bottom-up nanofabrication processes, but many self-assembled nanostructures contain defects and lack sufficient long-range order for certain nanotechnology applications. Here we investigate the formation of defects in a self-assembled array of spherical block-copolymer microdomains, using topographical templates to control the local self-assembly. Perfect ordered sphere arrays can form in both constant-width templates and width-modulated templates. For modulated templates, transition between configurations having a constant number of rows and configurations of stable arrays with varying numbers of rows is shown to be analogous to dislocation formation in an epitaxial thin film system. Based on the configuration transition energy and fluctuation energy, designed templates with a high tolerance for lithographical imperfections can direct precisely modulated block-copolymer nanostructures. This study provides insights into the design of hybrid systems combining top-down and bottom-up fabrication.     

Layer-by-layer assembly of nanowires for three-dimensional, multifunctional electronics

We report a general approach for three-dimensional (3D) multifunctional electronics based on the layer-by-layer assembly of nanowire (NW) building blocks. Using germanium/silicon (Ge/Si) core/shell NWs as a representative example, ten vertically stacked layers of multi-NW field-effect transistors (FETs) were fabricated. Transport measurements demonstrate that the Ge/Si NW FETs have reproducible high-performance device characteristics within a given device layer, that the FET characteristics are not affected by sequential stacking, and importantly, that uniform performance is achieved in sequential layers 1 through 10 of the 3D structure. Five-layer single-NW FET structures were also prepared by printing Ge/Si NWs from lower density growth substrates, and transport measurements showed similar high-performance characteristics for the FETs in layers 1 and 5. In addition, 3D multifunctional circuitry was demonstrated on plastic substrates with sequential layers of inverter logical gates and floating gate memory elements. Notably, electrical characterization studies show stable writing and erasing of the NW floating gate memory elements and demonstrate signal inversion with larger than unity gain for frequencies up to at least 50 MHz. The ability to assemble reproducibly sequential layers of distinct types of NW-based devices coupled with the breadth of NW building blocks should enable the assembly of increasing complex multilayer and multifunctional 3D electronics in the future.     

Direct drop-casting synthesis of all-inorganic lead and lead-free halide perovskite microcrystals for high-performance photodetectors

Due to the exciting photoelectric properties,better stability,and environmental-friendly nature,all-inorganic halide perovskites(AIHPs),especially the lead-free...     

From nanorings to nanodots by patterning with block copolymers

We demonstrate three different transfer patterns that can be achieved by use of a surface reconstructed block copolymer film where metal is evaporated onto the surface of the film, providing the contrast. Thin films of diblock copolymers having cylindrical microdomains oriented normal to the surface with long-range lateral order were used. Solvent reconstruction of the film, followed by a glancing angle metal evaporation and thermal annealing, led to three different decorations of the films with gold. These films were used as masks for pattern transfer of pores, columns, and rings to underlying substrate with high fidelity.     

Self-assembled monolayer-modified block copolymers for chemical surface nanopatterning

Thin-film poly(styrene-block-methyl methacrylate) diblock copolymer (PS-b-PMMA) is used to create chemically patterned surfaces via metal deposition combined with self-assembled monolayers (SAMs) and UV exposure. We use this method to produce surfaces that are chemically striped on the scale of a few tens of nanometers. Atomic force and transmission electron microscopies are used to verify the spatially localized organization of materials, and contact angle measurements confirm the chemical tunability of these scaffolds. These surfaces may be used for arraying nanoscale objects, such as nanoparticles or biological species, or for electronic, magnetic memory or photovoltaic applications.     

Cesium lead halide perovskite triangular nanorods as high-gain medium and effective cavities for multiphoton-pumped lasing

High-performance multiphoton-pumped lasers based on cesium lead halide perovskite nanostructures are promising for nonlinear optics and practical frequency upconversion devices in integrated photonics.However,the performance of such lasers is highly dependent on the quality of the material and cavity,which makes their fabrication challenging.Herein,we demonstrate that cesium lead halide perovskite triangular nanorods fabricated via vapor methods can serve as gain media and effective cavities for multiphoton-pumped lasers.We observed blue-shifts of the lasing modes in the excitation fluence-dependent lasing spectra at increased excitation powers,which fits well with the dynamics of Burstein-Moss shifts caused by the band filling effect.Moreover,efficient multiphoton lasing in CsPbBr3 nanorods can be realized in a wide excitation wavelength range (700-1,400 nm).The dynamics of multiphoton lasing were investigated by time-resolved photoluminescence spectroscopy,which indicated that an electron-hole plasma is responsible for the multiphoton-pumped lasing.This work could lead to new opportunities and applications for cesium lead halide perovskite nanostructures in frequency upconversion lasing devices and optical interconnect systems.     

Controllable optical emission wavelength in all-inorganic halide perovskite alloy microplates grown by two-step chemical vapor deposition

All-inorganic halide perovskites (IHP), CsPbX₃ (X = Cl, Br, I) exhibiting efficient optical emissions within the spectral range of 410 to 730 nm are potential candidates for many optoelectronic devices. Anion alloying of these IHPs is expected to achieve tunable emission wavelength covering the entire visible spectrum. Here, we developed a two-step chemical vapor deposition (CVD) process for growing quaternary IHP CsPbX₃ (X = Cl/Br and Br/I) alloys. By exploiting the fast diffusion of halide anions in IHPs, the alloy composition can be precisely controlled by the growth time of the respective layers once the growth of the individual ternary IHP is optimized. Hence complexities in the multi-parameter optimization in the conventional CVD growth of quaternary alloys can be mitigated. Using this process, we synthesized single crystalline, homogeneous and thermally stable CsPbCl₃(_1−X)Br_3x and CsPbBr₃(_1−X)I_3x perovskites alloy microplates and demonstrated continuously tunable emission covering the spectrum from 428 to 715 nm by varying the halide compositions in the alloys. These alloy microplates also exhibit room temperature amplified spontaneous emissions (ASE) along with strong photonic discharges from the microplate’s edges and hence are potentially useful as a gain medium as well as optical cavities for emissions with wavelengths covering the visible spectrum.