Conductive poly(3,4‐ethylenedioxythiophene): poly(styrene sulfonate) polymer glue as an ohmic and rectifying electrical contact for H‐terminated n‐Si and p‐Si wafers

An organic conductive glue based on a blend of poly(3,4‐ethylenedioxythiophene):poly(styrene sulfonate) (PEDOT:PSS) and d ‐sorbitol was examined for laminating conductors to crystalline silicon. The PEDOT:PSS glue functions as a high‐work‐function solution processable conductor and exhibits an ohmic contact on p‐type silicon and a rectifying contact on n‐type silicon. Under illumination, the n‐Si/PEDOT:PSS:d ‐sorbitol junctions exhibit current–voltage characteristics suggesting minority carrier trap states, leading to charge recombination at the silicon/polymer interface. Conductive glue for laminating to crystalline silicon is desirable for making electrical contacts to flexible materials such as molecular semiconductors, graphene or transparent conductive oxides. These materials could eliminate the need for metal contacts to the front face of silicon solar cells. Conductive glue could prove especially useful for laminating to textured silicon or novel micro‐ or nanostructured silicon materials. © 2018 Society of Chemical Industry     

Preparation of multi‐level honeycomb‐structured porous films by control of spraying atomized water droplets

Honeycomb‐structured porous films have been widely applied in various industrial areas such as chemical sensors, tissue engineering, and micro reactors. In this article, one novel self‐assembly approach is proposed to fabricate well‐ordered polyphenylene oxide honeycomb films by a facile control of spraying ultrasonic humidifier atomized water droplets. Proper spraying retention time is necessary for porous films formation with highly uniform pore size. The effect of atomized water droplets flux on the pore size and the regularity of the hexagonal arrays were experimentally investigated. The pore size became larger with increasing the solution concentration. Especially, honeycomb films with two‐level pores were fabricated by spraying atomized water droplets two times and the influence of interval time on the two‐level honeycomb films formation was investigated. Apart from analysis of structural characteristics, self‐assembly mechanism was also discussed. © 2014 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2014 , 131, 41163.     

Highly Stretchable and Sensitive Flexible Strain Sensor Based on Fe NWs/Graphene/PEDOT:PSS with a Porous Structure

With the rapid development of wearable smart electronic products, high-performance wearable flexible strain sensors are urgently needed. In this paper, a flexible strain sensor device with Fe NWs/Graphene/PEDOT:PSS material added under a porous structure was designed and prepared. The effects of adding different sensing materials and a different number of dips with PEDOT:PSS on the device performance were investigated. The experiments show that the flexible strain sensor obtained by using Fe NWs, graphene, and PEDOT:PSS composite is dipped in polyurethane foam once and vacuum dried in turn with a local linearity of 98.8%, and the device was stable up to 3500 times at 80% strain. The high linearity and good stability are based on the three-dimensional network structure of polyurethane foam, combined with the excellent electrical conductivity of Fe NWs, the bridging and passivation effects of graphene, and the stabilization effect of PEDOT:PSS, which force the graphene-coated Fe NWs to adhere to the porous skeleton under the action of PEDOT:PSS to form a stable three-dimensional conductive network. Flexible strain sensor devices can be applied to smart robots and other fields and show broad application prospects in intelligent wearable devices.     

Fabrication of Polymer Film with Extraordinary Conductive Anisotropy by Forming Parallel Conductive Vorticity‐Aligned Stripes and Its Formation Mechanism

In this work, anisotropic conductive film (ACF) is fabricated by shear‐flow induced assembly. It is found that an appropriate content of carbonaceous filler is needed for forming well‐ordered parallel vorticity‐aligned stripes and the content depends on the category of the filler. Interestingly, the lowest aspect ratio carbon black (CB) with lowest electrical conductivity is the best candidate for fabricating ACF. The film with CB stripes shows excellent conductive anisotropy: the electrical resistivity in the direction parallel to the CB stripes is almost eight orders of magnitude lower than that in the perpendicular direction. The formation mechanism of the vorticity‐aligned stripe is also investigated by the rheological measurement and the study of morphological evolution. It is found that the coalescence of dispersed phase or aggregates dominates the formation and growth of the stripe and negative value of the first normal stress difference drives the stripe to align along the vorticity direction.

     

Selective Coating of SnS on the Bio‐Inspired Moth‐Eye Patterned PEDOT:PSS Polymer Films

A new strategy for the selective coating of tin sulfide (SnS) on the surface of moth‐eye patterned (MEP) conducting polymer film is studied by considering the optical properties of the antireflective moth‐eye pattern and flexibility of polymer films. The semiconductor SnS is selectively coated on the surface of MEP microdomes of poly(3,4‐ethylenedioxythiophene) poly(styrene‐sulfonate) (PEDOT:PSS) film. The SnS coated MEP film is obtained by using pore selectively SnS thin layer functionalized polystyrene honeycomb‐patterned porous (HCP) film as a template. Aqueous PEDOT:PSS solution is poured on the SnS functionalized HCP films and detached for the fabrication of SnS coated MEP films. The films show a satisfactory photo‐responsive property under solar stimulated light illumination due to the antireflective MEP structure of PEDOT film and homogenous SnS coating on the surface of the conducting polymer.     

Enhanced Thermoelectric Performance of PEDOT:PSS Films by Sequential Post‐Treatment with Formamide

This paper reports a series of sequential post‐treatments using a polar solvent formamide to enhance the thermoelectric performance of poly(3,4‐ethylenedioxythiophene) doped with poly(styrene sulfonate) anions (PEDOT:PSS). The electrical conductivity of PEDOT:PSS films significantly increases from 0.33 S cm^?1 for the pristine film to ≈2929 S cm^?1 for the treated film and meanwhile the Seebeck coefficient maintains as high as 17.4 µV K^?1, resulting in a power factor of 88.7 µW m^?1 K^?2. Formamide is a polar solvent with a high boiling point of 210 °C and high dielectric constant of 109, and PSS has a good solubility in it. Post‐treatment with formamide causes not only the phase segregation of PEDOT and PSS but also the removal of insulating PSS, therefore leading to the reorientation of PEDOT chains and enhancement in mobility without altering the doping level considerably. The cross‐plane thermal conductivity also reduces from 0.54 to 0.19 W m^?1 K^?1 after the post‐treatment, leading to a figure of merit (ZT) value of 0.04 at room temperature.     

Electrical Properties and Relaxor Phase Evolution of Li‐Modified BNT‐BKT‐BT Lead‐Free Ceramics

By conventional ceramics sintering technique, the lead‐free 0.85Bi_0.5Na_0.5(1?x)Li_0.5xTiO₃‐0.11Bi_0.5K_0.5TiO₃‐0.04BaTiO₃ (x =0–0.15) piezoelectric ceramics were obtained and the effects of Li dopant on the piezoelectric, dielectric, and ferroelectric properties were studied. With increasing Li addition, the temperature‐dependent permittivity exhibited the normal ferroelectric‐to‐ergodic relaxor (FE‐to‐ER) transition temperature (T_FE‐ER, abbreviated as T_F‐R) decreasing down to room temperature. The increasing Li content also enhanced the diffuseness of the FE‐to‐ER transition behavior. For composition with x = 0.15, a large unipolar strain of 0.37% ( = S_max/E_max = 570 pm/V) was achieved under 6.5 kV/mm applied electric field at room temperature. Both unipolar and bipolar strain curves related to the temperature closely, and when the temperature reached the T_F‐R, the normalized strain achieved a maximum value (e.g., for x = 0.10, = 755 pm/V) owing to the electric‐field‐induced ER‐to‐FE state transition.     

A Bio‐Inspired and Biomass‐Derived Healable Photochromic Material Induced by Hierarchical Structural Design

Utilization of bionics to develop stimuli responsive polymers that can heal damage with excellent restorability is particularly attractive for a sustainable society. Herein, inspired by chameleons, a hierarchical structural design strategy is proposed and illustrated to fabricate a healable photochromic material based on a self‐healable polymeric matrix and a finely dispersed photochromic spirooxazine. The self‐healable polymeric matrix is fabricated via the integration of multiple hydrogen bonds (H bonds) and covalent cross‐links into a biomass‐derived elastomer. The dynamic nature and soft characteristics enable the as‐prepared elastomer superior extensibility as well as self‐healing ability, while the covalent cross‐links can assist the reassociation of ruptured H bonds. The representative elastomer exhibits an extensibility of 2600% and toughness of 42.76 MJ m^?3. Furthermore, it shows good self‐healing ability with complete recovery of scratch as well as restoration against 1900% of elongation and 24.1 MJ m^?3 of toughness after healing at 60 °C for 24 h. This combination of moderate toughness, good self‐healing ability, and smart photochromic property in biomass‐derived materials should largely improve their applicability, reliability, and sustainability in various materials and devices.     

Potassium–Sodium Niobate‐Based Lead‐Free Piezoelectric Ceramic Coatings by Thermal Spray Process

Potassium–sodium niobate (KNN)‐based piezoelectric ceramic coatings with single perovskite phase and dense morphology were obtained by thermal spray processing. The structure, morphology, and properties of the coatings deposited at different conditions were investigated, and excellent piezoelectric performance properties were demonstrated. The piezoelectric coefficient observed in the KNN‐based coatings in this study is about one order of magnitude higher than other thermal sprayed lead‐free piezoelectric coatings as reported in literature. With analyses on the differences in the characteristics between KNN and lead zirconate titanate (PZT) compositions and the reaction mechanisms of thermal spray and ceramic synthesis, the reasons for the successful formation of single‐phase perovskite structure with high crystallinity in the thermal sprayed KNN‐based coatings while not in PZT are explained.     

Enhanced Field‐Induced Strain in the Textured Lead‐Free Ceramic

Reactive template grain growth method was applied to prepare <001> grain oriented 0.94(Na_0.52K_0.48)NbO₃–0.06LiNbO₃ ceramics using plate‐like NaNbO₃ particles as template. A two‐step sintering procedure was put forward to obtain textured ceramics with electromechanical coupling factor k_p = 64%, piezoelectric constant d₃₃ = 220 pC/N, and in practical application the value of available (converse piezoelectric constant) is about 516 pm/V, which are much higher than these of random form with same composition. Based on the analysis for the behavior of piezoelectricity against the measuring frequency and the intensity of external field, a possible mechanism considering the interaction between defect dipoles induced by the doping of Cu²⁺ and spontaneous polarization dipoles was proposed to elucidate the field‐induced giant strain in textured ceramics. This study does not only provide an insight to the origin and coupling effect of two kinds of dipole but also renders a general approach of defect engineering to take advantage of point defect in ceramics realizing certain function enhancement.     

Large Electrostrain in K(Nb1−xMnx)O3 Lead‐Free Piezoelectric Ceramics

K(Nb_1?xMn_x)O₃ (KN_1?xM_x) ceramics with 0.005 ≤ x ≤ 0.015 were sintered at 1020°C through a normal sintering process without the formation of a liquid phase. They exhibited double polarization versus electric field (P–E) hysteresis and sprout‐shaped strain versus electric field (S–E) curves owing to the presence of a defect dipole (P_D), which was formed between the acceptor Mn³⁺ ion and the oxygen vacancy. Moreover, the aging process was not required to develop the P_D. The KN_1?xM_x ceramics exhibited a large strain of ~0.2% at 6.0 kV/mm. For the KN_0.985M_0.015 ceramic, this large strain was maintained after 10⁴ cycles of an electric field of 6.0 kV/mm. This ceramic also maintained a double hysteresis curve at 200°C. Therefore, the KN_0.985M_0.015 ceramic has a large electric field‐induced strain, along with good thermal and fatigue properties for multilayer piezoelectric actuators.     

TiO2/TNO homojunction introduced in a dye‐sensitized solar cell with a novel TNO transparent conductive oxide film

In this study, niobium‐doped titanium oxide (TNO) was employed for a novel transparent conductive oxide (TCO) film to construct a porous‐TiO₂/TNO homojunction in a dye‐sensitized solar cell (DSSC). However, considering a balance between the electrical and optical properties of the TCO film, the sheet resistance in TNO was tuned to be higher than that in a typical fluorine‐doped tin oxide (FTO). The photovoltaic performance of the cell with the TNO film (TNO cell) was optimized to be almost comparable to that with a conventional FTO film (FTO cell) by coating the surface of the porous‐TiO₂ layer with a thin alumina or magnesia film to block a back reaction within the cell. An electrochemical impedance measurement was conducted to determine the detailed photovoltaic performance from the viewpoint of electron transportation in the cell. R₁, the real part of ω₁, indicated that electron transportation at the porous‐TiO₂/TNO interface was more favorable than that at the porous‐TiO₂/FTO interface, which was supported by AC phase change in the cell at a high‐frequency range. We found that the homojunction newly introduced in the cell is one of the key concepts for developing a DSSC into a high‐performance photovoltaic device.     

Durable,Sensitive, and Wide‐Range Wearable Pressure Sensors Based on Wavy‐Structured Flexible Conductive Composite Film

Flexible pressure sensors have potential applications in human motion monitoring and electronic skins. To satisfy the practical applications, pressure sensors with a high sensitivity, a low detection limit, a broad response range, and an excellent stability are highly needed. Here, a piezoresistive pressure sensor based on wavy‐structured single‐walled carbon nanotube/graphite flake/thermoplastic polyurethane (SWCNT/GF/TPU) composite film is fabricated by a prestretching process. Due to the random wavy structure, high conductivity, and good flexibility, the prepared sensor displays a low detection limit of 2 Pa, a wide sensing range of 0–60 kPa, and a high sensitivity of 5.49 kPa^?1 for 0–50 Pa. Furthermore, the sensor shows a remarkable repeatability of over 1.1 × 10⁴, 9.0 × 10³, and 2.0 × 10³ pressure loading/unloading cycles at 50 Pa, 500 Pa, and 30 kPa, respectively, and a fast responsibility of 100–150 ms of loading response time and 400–600 ms of relaxation time. Therefore, the pressure sensor is successfully adopted to monitor both the large‐scale human activities (e.g., walk and jump) and the small‐scale signals (e.g., wrist pulse). Furthermore, a sensor array is assembled to map the weight and shape of an object, indicating its various potential applications including human–machine interactions, human health monitoring, and other wearable electronics.     

Solid‐Supported Rhodium(0) Nano‐/Microparticles: An Efficient Ligand‐Free Heterogeneous Catalyst for Microwave‐Assisted Suzuki–Miyaura Cross‐Coupling Reaction

Solid‐supported nano‐ and microparticles of rhodium(0) (SS‐Rh) were prepared and applied as a ligand free heterogeneous catalyst for Suzuki–Miyaura cross‐coupling reaction with wide range of substrate scope. A hitherto unknown Rh‐catalyzed Suzuki cross‐coupling reaction of aldehyde and cyanohaloarenes was observed rather than the usual nucleophilic arylation.The catalyst can be removed by simple filtration and recycled upto twelve runs without any deterioration of activity.     

A Practical Recycle of a Ligand‐Free Palladium Catalyst for Heck Reactions

Ligand‐free palladium can be recovered almost quantitatively from Heck reaction mixtures by filtration after its deposition on a carrier such as silica or celite. Subsequently, it is re‐activated to its original activity by adding a small amount of iodine or bromine prior to the next reaction cycle. The catalyst results in excellent yields and selectivities, even for the less reactive aryl bromides. A catalytic cycle based on anionic palladium intermediates is proposed.     

Gold‐ vs. Platinum‐Catalyzed Polycyclizations by O‐Acyl Migration. Solvent‐Free Reactions

Polycyclic derivatives incorporating a cyclopropyl group have been efficiently synthesized from propargyl acetates using platinum(II), gold(I) and gold(III) catalysis. These reactions which are also viable for the preparation of medium‐sized rings, proceed with a complete diastereocontrol and can also be run in neat conditions.     

New breathable films using a thermoplastic cross‐linked starch as a porogen

Breathable films, which find in variety of product applications, are conventionally made using mineral porogens such as calcium carbonate (CaCO₃). This article addresses a novel biodegradable and highly breathable film without inorganic porogens. Unexpectedly, a thermoplastic cross‐linked natural polymer (corn starch) was used successfully to create tortuous passages for film breathability. This concept was demonstrated using two types of thermoplastic cross‐linked corn starches as porogens and contrasted to control samples: native corn and chemically cross‐linked starches, respectively. The films discussed had increased breathability and mechanical properties relative to the control samples. The film morphology reveals that filler was irregular when thermoplastic starch or CaCO₃ was used. The difference in filler from chemically modified cross‐linked starch and thermoplastic cross‐linked starch was observable as well. It is believed that spherical particles provided by thermoplastic cross‐linked starch helps film debonding and porosity during the film stretch processes. © 2014 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2014 , 131, 41016.     

Electronically conductive porous TiN ceramics with enhanced strength by aqueous gel‐casting

In this paper, we report on a study of electronically conductive porous TiN ceramics prepared by aqueous gel‐casting. The effects of solid loading, sintering temperature, and sintering aids on the phase composition, microstructure, and volume fraction of porosity of the prepared porous TiN ceramics are studied. The SEM results show that porosity is uniformly distributed in all of the samples studied. With increasing solid loading and sintering temperature, the volume fraction of porosity decreases slowly. Moreover, the relationship between volume fraction of porosity and mechanical and electrical properties has also been investigated. Our results show that adding Y₂O₃‐TiO₂ as combined sintering aids results in a sharp decrease in the volume fraction of porosity, and the volume fraction range changes from 42%‐60% to 28%‐52%. Moreover, adding sintering aids results in an increase in flexural strength and electrical conductivity with a change in maximum value from 34.6 MPa and 2.3 × 10⁴ S?m^?1 to 101.6 MPa and 5.1 × 10⁴ S?m^?1, respectively.