Homogenizing out-of-plane cation composition in perovskite solar cells.

Perovskite solar cells with the formula FA1-xCsxPbI3, where FA is formamidinium, provide an attractive option for integrating high efficiency, durable stability and compatibility with scaled-up fabrication. Despite the incorporation of Cs cations, which could potentially enable a perfect perovskite lattice1,2, the compositional inhomogeneity caused by A-site cation segregation is likely to be detrimental to the photovoltaic performance of the solar cells3,4. Here we visualized the out-of-plane compositional inhomogeneity along the vertical direction across perovskite films and identified the underlying reasons for the inhomogeneity and its potential impact for devices. We devised a strategy using 1-(phenylsulfonyl)pyrrole to homogenize the distribution of cation composition in perovskite films. The resultant p-i-n devices yielded a certified steady-state photon-to-electron conversion efficiency of 25.2% and durable stability.

Construction of the Au Nanoparticle/Graphene Oxide/Au Nanotube (AuNP/GO/AuNT) Sandwich Membrane for Surface-Enhanced Raman Scattering Sensing.

Au nanotube-based composite membrane served as surface-enhanced Raman scattering (SERS) substrate with an ultralarge aspect ratio possesses an excellent flexibility and widely tunable surface plasmon resonance, and by introducing graphene oxide (GO) as a spacer layer, the SERS enhancement of the composite membrane is obviously better than those from the individual blocks of the Au nanotubes (AuNTS) membrane and the Au nanoparticle/graphene oxide (AuNP/GO) membrane. Such a "sandwich" (AuNP/GO/AuNT) structured membrane has a high SERS sensitivity and a wide tunability by controlling the size of Au nanoparticles and the thickness of graphene oxide, and the detection limits of the AuNP/GO/AuNT substrate for R6G and NBA are as low as 10-12 and 10-7 M, respectively; the large enhancement is attributed to the adsorption and chemical mechanism of graphene oxide and the physical mechanism of the Au nanoparticles and nanotubes (the electromagnetic field coupling between them).

Bidirectional Anions Gathering Strategy Afford Efficient Mixed PbSn Perovskite Solar Cells.

Mixed lead-tin (PbSn) perovskite solar cells (PSCs) possess low toxicity and adjustable bandgap for both single-junction and all-perovskite tandem solar cells. However, the performance of mixed PbSn PSCs still lags behind the theoretical efficiency. The uncontrollable crystallization and the resulting structural defect are important reasons. Here, the bidirectional anions gathering strategy (BAG) is reported by using Methylammonium acetate (MAAc) and Methylammonium thiocyanate (MASCN) as perovskite bulk additives, which Ac- escapes from the perovskite film top surface while SCN- gathers at the perovskite film bottom in the crystallization process. After the optoelectronic techniques, the bidirectional anions movement caused by the top-down gradient crystallization is demonstrated. The layer-by-layer crystallization can collect anions in the next layer and gather at the broader, enabling a controllable crystallization process, thus getting a high-quality perovskite film with better phase crystallinity and lower defect concentration. As a result, PSCs treated by the BAG strategy exhibit outstanding photovoltaic and electroluminescent performance with a champion efficiency of 22.14%. Additionally, it demonstrates excellent long-term stability, which retains ≈92.8% of its initial efficiency after 4000 h aging test in the N2 glove box.

Phase Change Microcapsules with a Polystyrene/Boron Nitride Nanosheet Hybrid Shell for Enhanced Thermal Management of Electronics.

Organic shell material and phase change material (PCM) have low thermal conductivity, which reduces the heat absorption and release rate of microencapsulated phase change materials (MEPCMs). Boron nitride nanosheets (BNNSs) with high thermal conductivity can not only stabilize the oil phase as the Pickering emulsifier but also improve the thermal conductivity of MEPCMs as one of the shell components, thus facilitating the heat conduction in the microcapsule system. Herein, MEPCM with paraffin wax (PW) as the core material and polystyrene (PS) modified by BNNSs as the shell material (PW@PS/BNNS MEPCMs) are synthesized via Pickering emulsion polymerization. The structure of PW@PS/BNNS MEPCMs can be regulated by tuning the PW and BNNS contents, to achieve high latent heat and thermal conductivity. In comparison to pure PW, the thermal conductivity of MEPCMs-5 wt % BNNSs increases by 63.76% at 25 °C. The PW@PS/BNNS powder possesses a latent heat capacity of 166.3 J/g, corresponding to a high encapsulation ratio of 80.77%. These properties endow the prepared MEPCMs with excellent thermal regulation properties. We also propose the formation mechanism of PW@PS/BNNS MEPCMs via Pickering emulsion polymerization for the first time, which will guide the MEPCM fabrication toward a reliable direction.

Effective Structure Control of Colloidal Molecules and the Morphology Evolution Mechanism Investigation.

Colloidal molecules (CMs), nonspherical clusters of a small number of particles, can be used as building blocks for self-assembly applications. Here, we propose a novel one pot method for CMs synthesis. First, poly(N-isopropylacrylamide-co-acrylic acid) (P(NIPAM-co-AA)) microgels were prepared by soap-free emulsion polymerization as seed particles, then monomer styrene and cross-linking agent divinylbenzene (DVB) were added, which could be polymerized by the remaining free radicals on the seed surface in situ. P(NIPAM-co-AA)-PS colloidal molecules with a series of morphologies such as popcorn-like, CO2-like, NH3-like, CH4-like and so on could be obtained. The effects of satellite colloid viscosity, interfacial tension, and polymer chain mobility on the number of satellite colloid have been investigated, and the formation mechanism of CMs is proposed based on morphology evolution investigation. Compared with the existing CM synthesis techniques, our method enables fabricating CMs from vinyl monomer in a facile and efficient way, and the scientific finding regarding the CMs formation will guide the CMs fabrication toward salable and reliable direction.

Widely tunable surface plasmon resonance and uniquely superior SERS performance of Au nanotube network films.

Three-dimensional Au network films with flexibility and transferability were fabricated based on sputtering deposition onto electrospun nanofibers as a template. The films are constructed using long Au nanotubes that are cross-linked with each other and that have dense nanoparticles on the tube wall surface. The surface plasmon resonance (SPR) peaks for the films are tunable in a wide range, from visible light to the near-infrared region, by tuning the inner diameter and/or wall thickness of the nanotubes. Such structured film exhibits significant surface-enhanced Raman scattering (SERS) activity with good signal uniformity and stability, and possesses great potential in thein situdetection of trace organic pollutants on a solid surface by simple transferring. This study provides a Au film with a unique structure and widely tunable SPR forin situSERS sensing and other needs.

Analysis of the microphase structure and performance of self-healing polyurethanes containing dynamic disulfide bonds.

Self-healable polyurethanes can be used in various fields for extended service life and reduced maintenance costs. It is generally believed that the shape memory effect is helpful for achieving a high healing efficiency. The morphological features were focused on in this study as microphase separation is one of the main factors affecting various performances of polyurethanes, including their shape memory behavior and mechanical properties. Microphase separation can be regulated by changing the content and types of the hard segments. With this in mind, polyurethanes from polycaprolactone diol, hexamethylene diisocyanate, and different chain extenders were synthesized, characterized, and designed as promising self-healing polymers. All the polyurethane specimens were equipped with a similar content of hard segments but diverse types, such as aliphatic, aromatic, and disulfide-bonded. Differential scanning calorimetry, thermogravimetric analysis, X-ray diffractometry, infrared spectroscopy, and atomic force microscopy were used to describe the microstructures of the polyurethanes, including the crystalline regions. The relationship between the microphase separation structures and material properties was focused on in this examination. Various properties, including the thermal stability, mechanical behavior, hydrophobicity, and self-healing efficiency showed significant differences due to the change in the hard segments' structure and multiphase distribution. The aliphatic disulfide stimulated the conformation of a proper microphase separation structure (the large heterogeneous structure at physical length scales as well as a more sufficient combination of soft and hard phases), which helped to improve the healing effect as much as possible by effective wound closure and the exchange reactions of disulfide bonds.

Construction of low melting point alloy/graphene three-dimensional continuous thermal conductive pathway for improving in-plane and through-plane thermal conductivity of poly(vinylidene fluoride) composites.

As the temperature of hot spots increases in electronic devices, thermal management is a key issue for maintaining a device's reliability and performance. The usual approaches of quickly extracting the heat from the hot spots have focused on aligning two-dimensional filler along the in-plane orientation in the polymer matrix. Meanwhile, improving the through-plane thermal conductivity of polymer-based composites is as important as in-plane thermal conductivity. In this study, poly(vinylidene fluoride) composites with three-dimensional continuous thermal conductive pathways of a low melting point alloy (LMPA)/graphene were prepared through a two-step method. Poly(vinylidene fluoride)@graphene (PVDF@Gr) microspheres were firstly prepared by an in-situ water-vapor induced phase separation method. Subsequently, PVDF@Gr/LMPA composites were obtained by hot-pressing after mixing the LMPA with the PVDF@Gr microspheres. Attributed to the unique solid-liquid phase transition advantage of the LMPA and the good matching of the phonon power spectrum between the LMPA and the graphene, the PVDF@4.8Gr/10LMPA composites with 4.8 vol% graphene and 10.0 vol% LMPA exhibited an outstanding in-plane thermal conductivity of 9.41 W m-1 K-1 and through-plane thermal conductivity of 0.35 W m-1 K-1, which was nearly increased by 245% and 130% compared to that of the PVDF@4.8Gr composites, respectively. The enhanced elasticity modulus and reduced thermal expansion coefficient were attributed to the LMPA constructing a three-dimensional continuous thermal conductive pathway along with the graphene and reducing interface thermal resistance. This study offeres a straightforward and repeatable method for fabricating highly thermally conductive polymer composites and widens the application of LMPAs in the fields of thermal management.

Bifunctional reduced graphene oxide/V2O5 composite hydrogel: fabrication, high performance as electromagnetic wave absorbent and supercapacitor.

Multifunctional graphene hydrogels have attracted great attention aimed at practical applications. Herein, the novel and bifunctional composite hydrogel containing reduced graphene-oxide nanosheets (RGO) and V2O5 nanobelts (RGO/V2O5) is successfully prepared for the first time. Surprisingly, tridimensional (3D) RGO/V2O5 composite hydrogels cannot only be used as high-performance electromagnetic (EM) wave absorbents; they also exhibit excellent properties suitable for supercapacitor electrodes. The composites exhibit a maximum absorption of up to -21.5 dB. In particular, a composite hydrogel showed a bandwidth of 6.63 GHz, corresponding to a reflection loss at -10 dB, which opens the possibility for the use of 3D graphene with other functional nanomaterials as lightweight and high-performance EM wave absorption materials. Remarkably, the composite hydrogel is capable of delivering a high specific capacitance of about 320 F g(-1) at a current density of 1.0 A g(-1) .

Two coupled effects of sub micron silica particles on the mechanical relaxation behavior of ethylene-propylene-diene rubber chains.

This article studied the influence of silica (SiO2) particles on the crosslinked network and the molecular mobility of ethylene-propylene-diene (EPDM) rubber chains by dynamic mechanical analysis (DMA). When SiO2 fraction is lower than 8 phr, the chain segments that participate in the glass-rubber transition (α transition) decrease with increasing the SiO2 content, while the whole crosslinked network is almost unaffected by the presence of SiO2. When the SiO2 fraction increases to about 20 phr, there appears a new tan δ peak (α' transition) above the α transition. This could be because the crosslinking reaction took place only on a small scale and the formed network became gradually incomplete when the content of the particles exceeded some critical value, and the α' transition is attributed primarily to the motion of non-elastic network chains loosely attached to the three-dimensional network. However, at SiO2 loadings higher than 40 phr, the crosslinking density was kept basically constant. The α' transition is hindered by a restriction of the chain mobility due to SiO2. The different changes of α' transition depended on the two coupled effects of SiO2, including restricting the chain mobility and decreasing the crosslinking density. Correspondingly, with increasing the mobility of EPDM chains and SiO2-induced strengthening, the mechanical properties of EPDM composite are dramatically improved. With the addition of 20 phr of SiO2 in the EPDM, a 113% increase in the elongation at break, a 510% increase in the fracture energy, and a 283% increase in the tensile strength are achieved.

The effects of polydimethylsiloxane on transparent and hydrophobic waterborne polyurethane coatings containing polydimethylsiloxane.

The effects of polydimethylsiloxane (PDMS) on phase separation, optical transmittance and surface properties including surface composition, morphology and wettability of waterborne polyurethane (WPU) containing PDMS were investigated. After the introduction of PDMS into the WPU backbone by polymerization, the large difference in the solubility parameter of the non-polar PDMS segment and the high-polar urethane segments promoted PDMS enrichment at the air-polymer interface and enhanced phase separation, resulting in rough structures. Accordingly, the combination of PDMS enrichment and the rough structures contributed to the high or superhydrophobic surfaces and the highest contact angle with water achieved was 156.5°. The optical transmittance of the highly hydrophobic coatings reached about 78-87% throughout most of the visible light region. Importantly, the highly hydrophobic and transparent properties will greatly broaden the applications of WPU, showing potential for the environmental protection and industrial applications.

High-Loading Smart Carrier Containing 2-Mercaptobenzimidazole-Zn2+-Polydopamine with pH-Responsive Function to Fabricate High-Performance Waterborne Epoxy Anticorrosion Coatings.

Corrosion inhibitor additives are considered to be one of the effective methods to slow down the corrosion of metals, but the corrosion inhibitors will decompose and lose their effect in a long-term corrosive environment. In this work, a smart corrosion inhibitor carrier 2-mercaptobenzimidazole-Zn2+-polydopamine@graphite (MZPG) with excellent pH response was designed and synthesized using a one-pot method. This corrosion inhibitor carrier not only has a very high 2-mercaptobenzimidazole (MBI) loading capacity (38.0%) but also maintains a very low MBI activity to inhibit the decomposition of MZPG in the environment as much as possible. The MZPG/epoxy (MZPG/EP) coatings prepared by the spraying method showed excellent mechanical properties. Electrochemical and salt spray tests showed that the MZPG/EP coatings (1.20 × 1010 Ω·cm2) have excellent corrosion resistance with Rp values up to 3 orders of magnitude higher than that of the EP coating (1.25 × 107 Ω·cm2). Notably, the MZPG/EP coatings maintained good corrosion resistance under acidic conditions due to the pH-responsive release of corrosion inhibitors. This is of great significance for the future development of coatings for highly corrosive environments.

A high-performance, oxidation resistance and flexible Zn@MXene/cellulose nanofibers electromagnetic shielding film.

Next-generation wearable electromagnetic interference (EMI) materials need to be provided with oxidation resistance, lightness, and flexibility. In this study, a high-performance EMI film with synergistic enhancement of Zn2+@Ti3C2T x MXene/cellulose nanofibers (CNF) was found. The unique Zn@Ti3C2T x MXene/CNF heterogeneous interface facilitates the loss of interface polarization, making the total electromagnetic shielding effectiveness (EMI SET) and shielding effectiveness per unit thickness (SE/d) of the films reach 60.3 dB and 5025 dB mm-1, respectively, in the X-band at the thickness of 12 µm ± 2 µm, significantly exceeding that of other MXene-based shielding materials. In addition, the coefficient of absorption gradually increases with the increasing CNF content. Moreover, under the synergistic effect of Zn2+, the film shows excellent oxidation resistance (maintaining stable performance after 30 days), greatly exceeding the previous test cycle. Furthermore, the mechanical performance and flexibility of the film are greatly enhanced (tensile strength at 60 MPa, and maintaining stable performance after 100 times bending tests) due to the CNF and hot-pressing process. Therefore, with the enhancement of the EMI performance, high flexibility and oxidation resistance under high temperature and high humidity conditions, the as-prepared films have wide practical significance and broad application prospects in a series of complex applications, such as flexible wearable fields, ocean engineering fields and high-power device packaging fields.

Self-healing liquid metal hydrogel for human-computer interaction and infrared camouflage.

Due to their mechanical flexibility, conductive hydrogels have been widely investigated in the fields of flexible electronics and soft robots, but their non-negligible disadvantages, such as poor toughness and limited self-healing, severally restrict their practical application. Herein, gallium indium alloy (EGaIn) is utilized to initiate the polymerization and simultaneously serve as flexible fillers to construct a super-stretchable and self-healing liquid metal/polyvinyl alcohol/p(acrylamide-co-octadecyl methacrylate) (liquid metal/PVA/P(AAm-co-SMA)) double network hydrogel (LM hydrogel). The synergistic effect of the rigid PVA microcrystal network and the ductile P(AAm-co-SMA) hydrophobic network, together with the ionic coordination and hydrogen bonds between polymer networks (multiple physical cross-links), endow the LM hydrogel with excellent super-stretchability (2000%), toughness (3.00 MJ m-3), notch resistance, and self-healing property (healing efficiency > 99% at 25 °C after 24 h). The LM hydrogel exhibits sensitive strain sensing behavior, allowing human-computer interaction to achieve motion recognition and health monitoring. Significantly, owing to the excellent photothermal effect and low infrared emissivity of EGaIn, the LM hydrogel reveals great potential in infrared camouflage. The work of self-healing conductive liquid metal hydrogels will promote the research and practical application of hydrogels and liquid metal in intelligent devices and military fields.

Layer-by-layer inkjet printing of fabricating reduced graphene-polyoxometalate composite film for chemical sensors.

Graphene oxide (GO) nanosheets and polyoxometalate such as H(3)PW(12)O(40) (PTA) are prepared into a multilayer film via a layer-by-layer inkjet printing method. The GO/PTA composite thin film shows linear, uniform and regular layer-by-layer growth. Under UV-irradiation, a photoreduction reaction takes place in the film which converts GO to reduced GO (rGO) due to the photoreduction activity of polyoxometalate clusters. According to the cyclic voltammograms measurement, the rGO/PTA composite film displays good electrocatalytic activity for the oxidation of dopamine (DA). The oxidation peak current (I(pa)) increases gradually with increasing the dopamine concentration, which may be used in electrochemical biosensors.

Controlled Transformation of Liquid Metal Microspheres in Aqueous Solution Triggered by Growth of GaOOH.

Liquid metals (LMs) are playing an increasingly important role in the fields of flexible devices, electronics, and thermal management due to their low melting point and excellent thermal and electrical conductivity, and the transformation of LMs in deionized water has recently received much attention. In this paper, we investigate the transformation process of EGaIn microspheres in deionized water and propose a two-step process of microspherical transformation, whereby the microspheres are first deformed into a spindle shape and then into lamellar nanorods. It is also shown that the growth of GaOOH crystals drives the transformation. Based on this result, EGaIn microspheres with controllable transformation could be prepared, such as spindle or lamellar rod shapes, extending the application area of LMs.

Preparation of poly glycidyl methacrylate (PGMA) chain-grafted boron nitride/epoxy composites and their thermal conductivity properties.

Surface modification of hexagonal boron nitride (h-BN) has the problem of reducing the interfacial thermal resistance, which has hindered its application in thermal conductive composites. Herein, poly glycidyl methacrylate (PGMA) chains were grafted onto the h-BN surface by simple radical polymerization; the thermal conductivity of epoxy (EP) composites was improved by adding the as-grafted h-BN-PGMA to EP resin. When the filling volume of h-BN-PGMA was 4, 10 or 16 vol%, the thermal conductivity of EP composite increased by 160%, 298% or 599%, respectively. Moreover, the h-BN surface modification was beneficial to enhance the compatibility between the filler and the EP matrix. Compared to EP/h-BN, the EP/h-BN-PGMA had higher thermal conductivity (1.197 W m-1 K-1) under the same filling amount (16 vol%). Moreover, excellent dielectric properties and thermal stability indicated that EP/h-BN-PGMA composites were excellent thermal interface materials (TIMs) and could be applied in the field of thermal management. The preparation process is environmentally friendly, easy to operate, and suitable for large-scale practical applications.

Detection and characterization of folded-chain clusters in the structured melt of isotactic polypropyl-ene.

Despite ceaseless efforts in past decades, the memory effect of semi-crystalline polymers has not been elucidated completely yet. An important reason why is that residual lamellar crystals in the structured melt are difficult to characterize. Recently, we developed a new small-angle X-ray scattering (SAXS) theory [Li et al. (2019). IUCrJ, 6, 968-983] and Fourier transform method [Li et al. (2020). CrystEngComm, 22, 3042-3058] for lamellar crystals that could derive structural information from SAXS readily. In this study, we tried to employ the new theory and method to characterize residual lamellar crystals in the structured melt. It was found that although scattering peaks cannot be observed in raw scattering profiles, they actually exist. Subtracting free-melt scattering and multiplying by q 4 benefit the observation of these weak scattering peaks. With the new Fourier transform method, it was found that indeed as proposed previously, thicker lamellar crystals exist in the structured melt. To determine the lateral size of residual lamellar crystal especially, a new method was developed under the guidance of the new theory. With the new method, it was found that although the crystallinity is very low (∼1% at 174°C), the lateral sizes in the structured melts are still large, e.g. 45.3 nm at 174°C, much greater than the critical nucleation size. This implies that these residual lamellar crystals can act as athermal nuclei after quenching to a lower temperature, as proposed by Ziabicki & Alfonso [(1994). Colloid Polym. Sci. 272, 1027-1042; (2002). Macromol. Symp. 185, 211-231] more than 20 years ago. The methodologies proposed here could also be applied to other polymer lamellar systems.

Stitching Graphene Sheets with Graphitic Carbon Nitride: Constructing a Highly Thermally Conductive rGO/g-C3N4 Film with Excellent Heating Capability.

Driven by the evolution of electronic packaging technology for high-dense integration of high-power, high-frequency, and multi-function devices in modern electronics, thermal management materials have become a crucial component for guaranteeing the stable and reliable operation of devices. Because of its admirable in-plane thermal conductivity, graphene is considered as a desired thermal conductor. However, the promise of graphene films has been greatly weakened as the existence of grain boundaries lead to a high extent of phonon scattering. Here, a stitching strategy is adopted to fabricate an rGO/g-C3N4 film, where 2D g-C3N4 works as a linker to covalently connect adjacent rGO sheets for expanding the size of graphene and forming an in-plane rGO/g-C3N4 heterostructure. The in-plane thermal conductivity of the rGO/g-C3N4 film reaches 41.2 W m-1 K-1 at a g-C3N4 content of only 1 wt %, which increased by 17.3% compared to pristine rGO. The interfaced thermal resistance between rGO and g-C3N4 is further examined by non-equilibrium molecular dynamics simulations. Furthermore, owing to the unique light absorption and welding ability of g-C3N4, the rGO/g-C3N4 film presents superior solar-thermal and electric-thermal responses to controllably regulate the chip temperature against overcooling. This work provides a facile approach to construct a large-sized rGO sheet and combines heat dissipation and heating capability in the same thermal management material for future electronics.

A new small-angle X-ray scattering model for polymer spherulites with a limited lateral size of the lamellar crystals.

As is well known, polymers commonly form lamellar crystals, and these assemble further into lamellar stacks and spherulites during quiescent crystallization. Fifty years ago, Vonk and Kortleve constructed the classical small-angle X-ray scattering theory (SAXS) for a lamellar system, in which it was assumed that the lamellar stack had an infinite lateral size [Vonk & Kortleve (1967 ▸), Kolloid Z. Z. Polym. 220, 19-24]. Under this assumption, only crystal planes satisfying the Bragg condition can form strong scattering, and the scattering from the lamellar stack arises from the difference between the scattering intensities in the amorphous and crystalline layers, induced by the incident X-ray beam. This assumption is now deemed unreasonable. In a real polymer spherulite, the lamellar crystal commonly has dimensions of only a few hundred nanometres. At such a limited lateral size, lamellar stacks in a broad orientation have similar scattering, so interference between these lamellar stacks must be considered. Scattering from lamellar stacks parallel to the incident X-ray beam also needs to be considered when total reflection occurs. In this study, various scattering contributions from lamellar stacks in a spherulite are determined. It is found that, for a limited lateral size, the scattering induced by the incident X-ray beam is not the main origin of SAXS. It forms double peaks, which are not observed in real scattering because of destructive interference between the lamellar stacks. The scattering induced by the evanescent wave is the main origin. It can form a similar interference pattern to that observed in a real SAXS measurement: a Guinier region in the small-q range, a signal region in the intermediate-q range and a Porod region in the high-q range. It is estimated that, to avoid destructive interference, the lateral size needs to be greater than 11 µm, which cannot be satisfied in a real lamellar system. Therefore, SAXS in a real polymer system arises largely from the scattering induced by the evanescent wave. Evidence for the existence of the evanescent wave was identified in the scattering of isotactic polypropyl-ene. This study corrects a long-term misunderstanding of SAXS in a polymer lamellar system.