As-fabricated Device Research Articles

Autonomous Chemistry Enabling Environment-Adaptive Electrochemical Energy Storage Devices

Autonomous Chemistry Enabling Environment-Adaptive Electrochemical Energy Storage Devices

Energy Harvesting Using Cotton Fabric Embedded with 2D Hexagonal Boron Nitride.

Continuous health monitoring through sensitive physiological signals (using a wearable device) is crucial for the early detection of heart diseases and breathing problems. Here, we have developed a flexible hBN/cotton hybrid device that can detect minor signals such as heartbeat and breathed-out air pressure. Systematic observation of the real-time motion sensing showed a peak-to-peak voltage output of ∼1.5 V for each heart rate pulse. The as-fabricated device showed a high voltage output of up to ∼10 V upon applying a pressure of ∼3 MPa. The FTIR results and DFT calculation suggested a chemical interaction between hBN and cellulose, giving rise to flat band characteristics and partially filled σ-bonding (sp2) hybridization. The atomic-scale chemical interface between atomically thin hBN and surface functional groups present on cotton resulted in charge localization and enhanced output voltage. An hBN/cotton hybrid device can bring new insights and opportunities to develop a self-charging and health-monitoring energy-harvesting cloth.

Design of ultranarrow-bandgap acceptors for efficient organic photovoltaic cells and highly sensitive organic photodetectors

The fabrication of multifunctional electronic devices based on the intriguing natures of organic semiconductors is crucial for organic electronics. Ultranarrow-bandgap materials are in urgent demand for fabricating high-performance organic photovoltaic (OPV) cells and highly sensitive near-infrared organic photodetectors (OPDs). By combining alkoxy modification and an asymmetric strategy, three narrow-bandgap electronic acceptors (BTP-4F, DO-4F, and QO-4F) were synthesized with finely tuned molecular electrostatic potential (ESP) distributions. Through the careful modulation of electronic configurations, the optical absorption onsets of DO-4F and QO-4F exceeded 1 μm. The experimental and theoretical results suggest that the small ESP of QO-4F is beneficial for achieving a low nonradiative voltage loss, while the large ESP of BTP-4F can help obtain high exciton dissociation efficiency. By contrast, the asymmetric acceptor DO-4F with a moderate ESP possesses balanced voltage loss and exciton dissociation, yielding the best power conversion efficiency of 13.6% in the OPV cells. OPDs were also fabricated based on the combination of PBDB-T:DO-4F, and the as-fabricated device outputs a high shot-noise-limited specific detectivity of 3.05 × 1013 Jones at 850 nm, which is a very good result for near-infrared OPDs. This work is anticipated to provide a rational way of designing high-performance ultranarrow-bandgap organic semiconductors by modulating the molecular ESP.

A self-powered photoelectrochemical aptasensor based on dual-photoelectrode photofuel cell for chloramphenicol detection

Inspired by the power generation mechanism of photofuel cell (PFC), a sensitive chloramphenicol (CAP) detection method was developed through the dual-photoelectrode photoelectrochemical (PEC) aptasensor. Assisted with the localized plasma resonance effect (LSPR) of AuNPs, the three-dimensional (3D) graphite carbon nitride (g-C3N4) was acted as the photoanode to output high and stable photocurrent. The photocathode used porous metal organic framework (MOF) and Cu2O to form an N doped core-shell structure, which improved the aptasensor performance by co-participating in the photoresponse with the photoanode. The oxidation-reduction reaction together with the bias voltage of two electrodes completed a PFC system, which realized spontaneously power supply capability. In addition to the sensitivity, the selectivity, stability and repeatability of the as-fabricated device were also guaranteed, which was suitable for practical application. The novel PFC-based dual-photoelectrode PEC sensing system can be regarded as a potential method for antibiotics detection.

High-performance large-area blade-coated perovskite solar cells with low ohmic loss for low lighting indoor applications

Emerging hybrid organic–inorganic perovskites with superior optoelectronic property demonstrate promising prospect for photovoltaic (PV) applications, in particular for low-lighting indoor applications e.g. within internet of things (IoT) networks or low-energy wireless communication devices. In order to prepare devices with high power output under low-illumination conditions, scalable fabrication techniques are preferred for large-area perovskite solar cells. In additions, one of the key parameters to achieve high-efficiency large-area perovskite solar cells is to minimize the ohmic loss to further boost the solar cell efficiency. Herein, a one-step blade-coating method assisted by hexafluorobenzene (HFB) was developed to deposit dense, large-area smooth and high-quality perovskite films with low ohmic loss. The as-fabricated devices demonstrated power conversion efficiency (PCE) of 20.7% (area of 0.2 cm2) and 16.5% (1 cm2), respectively, under standard (AM 1.5G) illumination conditions. Besides, the large-area (1 cm2) devices demonstrated a remarkable PCE of ∼ 33.8% and ∼ 30.0% under 1000 lx and 100 lx illumination provided by white light-emitting diode (LED) lamp, respectively. We exhibited a series-connected stack of large-area (totally active area ∼ 4 cm2) perovskite photovoltaic device powering up a LED under common indoor environment as an indoor self-power indicator lamp. The analysis using a single diode model suggests that the high performance of the large-area devices under low-lighting indoor conditions is highly associated with the largely reduced ohmic losses, which particularly indicate that the perovskite films by a facile and scalable blade-coating method. The presented scalable approach paves the way to designing high-performance perovskite solar cells for a variety of emerging indoor PV applications.

A spongy Rhizophora mucronata derived ultra-high surface area activated carbon for high charge density supercapacitor device

Biomass-derived activated carbons are considered promising materials for numerous commercial applications owing to their outstanding properties. The current work demonstrates a successful two-step synthesis strategy, resulting in the conversion of spongy Rhizophora mucronata fruit into an ultra-high surface area activated carbon for energy storage. The best material chosen upon optimization, displayed a very large specific surface area of ~3347 m2/g due to the combined effect of the KOH activation mechanism as well as the liberation of oxygen from the air sacs of aerenchyma present in the biomass. This ultra-high surface area activated carbon exhibited a specific capacitance of 282 F/g at 0.5 A/g in three-electrode configuration with a 6 M KOH electrolyte. Owing to such a huge surface area, a two-electrode symmetric device MGAC-3//MGAC-3 was fabricated that revealed a specific capacitance of 200 F/g at 0.5 A/g. A remarkable energy density of 27.52 Wh/kg at a power density of 500 W/kg was achieved for the as-fabricated symmetric device which makes it a promising high charge density electrode material. Notable stability was achieved with Coulombic efficiency of 99.2% with capacitance retention of 88.3% after 20,000 prolonged charge-discharge cycles.

Overall High-Performance Near-Infrared Photodetector Based on CVD-Grown MoTe2 and Graphene Vertical vdWs Heterostructure

Two-dimensional (2D) materials, such as graphene and transition metal dichalcogenides (TMDCs), are highly appealing in the fields of electronics, optoelectronics, energy, etc. Graphene, with high conductivity and high carrier mobility, is an excellent candidate for transparent electrodes. TMDCs have remarkably strong light absorption in the range of visible to infrared wavelength. High-performance photodetectors are expected to achieve through the combination of graphene and TMDCs. Nowadays, near-infrared (NIR) photodetectors play significant roles in many areas. MoTe2 with bandgap energy of about 1.0 eV in its bulk form is a promising material for cost-saving NIR photodetectors. Thus far, only a few of the reported studies on NIR photodetectors built on MoTe2/graphene heterostructures have achieved high responsivity and short response time simultaneously in one device. In this study, we fabricate graphene–MoTe2–graphene vertical van der Waals heterostructure devices through chemical vapor deposition (CVD) growth, wet transfer method, and dry etching technique. Under 1064 nm laser illumination, we acquire responsivity of as high as 635 A/W and a response time of as short as 19 μs from the as-fabricated device. Moreover, we acquire higher responsivity of 1752 A/W and a shorter response time of 16 μs from the Al2O3-encapsulated device. Our research drives the application of 2D materials in the NIR wavelength range.

Flexible pCu2Se-nAg2Se thermoelectric devices via in situ conversion from printed Cu patterns

Flexible thermoelectric (TE) devices have great potential in wearable electronics, but there is great challenge to realize robust TE device with high performance via feasible integration process. Herein, based on precisely printed copper patterns, a flexible pCu2Se-nAg2Se TE device is initially realized by in situ ion exchange reaction. The as-prepared Cu2Se and Ag2Se films possess typical hierarchical defects including atomic scale vacancies, the nanosheet fragments and microscale porous structure, which could significantly scatter phonons in wide frequency range. Accordingly, ultra-low thermal conductivity (Cu2Se: 0.13 W m−1 K−1; Ag2Se: 0.15 W m−1 K−1) and optimal ZTs (Cu2Se: 0.5; Ag2Se: 0.7) are achieved. Meanwhile, the as-fabricated pCu2Se-nAg2Se TE device exhibits an excellent power density of 13.4 W m−2 at a temperature gradient of 40 K, which is among the highest values of printed in-plane film devices. Furthermore, the good adhesion between TE films and porous PI substrate endowed excellent flexibility and stability of pCu2Se-nAg2Se devices.

Surface engineered environment-stable red-emitting fluorides for white light emitting diodes

Poor water stability is the main problem of commercialized Mn 4+ -doped fluorides for white light emitting diode (WLED) application. This work proposes a surface engineering strategy to rebuild a Mn 4+ -free fluoride shell on fluorides to effectively resist the destruction from water molecules. By simple processing using glyoxylic acid (GA) solution, the moisture resistance of the red-emitting fluorides can be significantly improved. The photoluminescence (PL) quantum efficiency (QE) of the surface-engineered K 2 SiF 6 :Mn 4+ (KSFM-GA) still maintain 98.43% after water immersion for 360 h, in sharp contrary to the untreated one (its PLQE decreases to 59.79%). Additionally, PL intensity of the hydrolyzed KSFM can be recovered to 99.1% through the treatment of the reducing GA solution. By using the high-stability KSFM-GA red phosphor, the as-fabricated high-performance warm-WLED device can still maintain 84.6% in luminous efficacy, higher than that (79.6%) with the untreated KSFM, after 500 h of aging in a high temperature (85 °C) and high humidity (85%) environment. • The surface engineering strategy is very simple for processing the commercial fluorides. • The surface reconstructed fluorides well remain the morphology and photoluminescence (PL) properties. • The PL intensity of the surface-engineered fluorides is almost unchanged even after being immersed in water for 360 h. • The reducing glyoxylic acid solution can fully restore the photoluminescence intensity of the hydrated fluorides. • The white-LED device with the surface-engineered fluoride shows improved color stability.

CdS based chemiresistor with Schottky contact: Toxic gases detection with enhanced sensitivity and selectivity at room temperature

Surmounting the selectivity issue of gas sensors and detecting low ppm concentration of gases is highly significant for widespread deployments of sensors to build networks in applications including vehicular emission, fuel-based household appliances, and industrial emissions. Herein, a strategy is proposed to improve the selectivity and sensitivity of the cadmium sulfide (CdS) based sensor via changes in contact material by utilizing different metals. CdS was deposited via the SILAR method on three different glass substrates which have Au, ITO, and Ag contacts, respectively, through which Schottky barrier height (SBH) was adjusted between CdS and metal contact. CdS was thoroughly verified by structural and morphological characterization techniques. As-fabricated devices were tested, and gas sensing results suggest that Au and ITO contacts have significantly superior selectivity towards NO2 and CO gases over other gases. Further, experimental values reveal that sensors can detect up to 0.3 ppm and 1.25 ppm, respectively. Good selectivity can be attributed to the regulation of the SBH. Additionally, as-fabricated devices displayed good long-term stability and short response and recovery times. The present study may provide a rational design for fabricating a high-performance chemiresistive gas sensor for the detection of sub-ppm levels of hazardous gases present in the environment.

Solution-processed light-induced multilevel non-volatile wearable memory device based on CsPb2Br5 perovskite.

Despite the recent advancements in memory devices, the quest for building materials with low power consumption is still on, with the ultimate focus on the durability of the system and reliability and reproducibility of its performance. Halide perovskites (HPs), which have several intriguing photoelectrical traits, have recently been utilized for memory applications; one of the highlights of these materials is the ionic-motion-based fast switching in their crystal structure. In this work, a CsPb2Br5 film is applied as a switching layer to implement memory devices with a flexible Al/CsPb2Br5/ITO-PET structure. The device exhibits a pronounced bipolar resistive switching (RS) characteristic at low operating voltage. The as-fabricated flexible device presented RS features with no initial forming process, concentrated distributions of high and low resistance states (HRS and LRS), uniform switching, endurance over 100 cycles, and a long retention time of 103 s with a high on/off ratio of around 102. Multilevel data-storage capability was also observed via subtle control of the compliance current (CC). Considering the current demand for smart, wearable, and flexible electronic gadgets, the current-voltage (I-V) characteristics of the as-fabricated all-inorganic halide-perovskite-based memory device were further explored under different bending conditions to determine its electrical reliability and mechanical stability. This flexible device exhibited no discernible difference in device performance under flat or bent conditions, and the performance remained nearly the same even after 500 bending cycles. In addition to control of the RS effect of the device using an electrical field, the performance of the device under light was also explored. Blue light modulates the resistive states by regulating the condition of photo-generated electron-hole pairs, and the SET and RESET voltages are changed from 2.34 to 2.14 V and from -2.04 to -1.90 V, respectively. The observed RS behavior is explained on the basis of the creation and partial annihilation of conductive multifilaments, which is dominated by the migration of bromine ions and their associated vacancies in the HP layer. We believe that this work will offer a new context to understand the intrinsic characteristics of HPs for RS applications at low voltage and validate their potential in the design of next-generation stable and nonvolatile memory devices for future flexible electronic systems.

Donor-acceptor-type poly[chalcogenoviologen-alt-triphenylamine] for synaptic biomimicking and neuromorphic computing

SummaryPolymer memristors are preeminent candidates for low-power edge computing paradigms. Poly[chalcogenoviologen-alt-triphenylamine] (PCVTPA) has been synthesized by direct coupling of chalcogeno-viologen as electron acceptor and 4-(bromomethyl)-N-(4-(bromo-methyl)phenyl)-N-phenylaniline as electron donor. The introduction of chalcogen atoms (S, Se, Te) into viologen scaffolds can greatly improve electrical conductive, electrochemical, and electrochromic properties of the materials when compared with the conventional viologens. Taking PTeVTPA as an example, the as-fabricated electronic device with a configuration of Al/PTeVTPA/ITO exhibits excellent multilevel storage and history-dependent memristive switching performance. Associated with the unique memristive behavior, the PTeVTPA-based device can not only be used to emulate the synaptic potentiation/depression, the human's learning and memorizing functions, and the transition from short-term synaptic plasticity to long-term plasticity but also carry out decimal arithmetic operations as well. This work will be expected to offer a train of new thought for constructing high-performance synaptic biomimicking and neuromorphic computing system in the near future.

Borassus flabelliferFruit Flesh Derived Hierarchical Porous Partly Graphitic Carbon as a Sustainable Electrode for Supercapacitors

The present work provides a straightforward two-step strategy of carbonization, followed by KOH activation, for transforming Borassus flabellifer fruit flesh, one of the cost-effective and sustainable lignocellulose biomass to porous activated carbon for utilization in energy storage systems. The acquired activated Borassus flabellifer fruit flesh (ABFF) carbon exhibits features like high surface area (∼1087.8 m2 g–1) with surface functionalities, hierarchical porous morphology (presence of micropores and mesopores), together with some partially graphitic domain, some of the prerequisites for demonstration of excellent electrochemical performance. Taking advantage of the structural features and chemical composition, the ABFF carbon, when assembled in a symmetrical two-electrode configuration, exhibits an impressive specific capacitance of 226 F g–1 and 159 F g–1 in 1 M H2SO4 and neat ionic liquid (IL) EMIMBF4 electrolyte. The as-fabricated symmetric device attained a maximum energy density of 8 Wh kg–1 in the aqueous medium, while an enhanced energy density of 50 Wh kg–1 was achieved in the nonaqueous medium.

Chemical growth and study of low intensity sensing ability of nanobranch and nanorod structured SnO2 UV detector

Ultra violet (UV) photodetector (PD) has been gaining attention in the fields of environment, medical, civil, and military realms, etc. In this report, nanostructured tin oxide (SnO2) thin films were deposited by a hot-wall nebulizer spray pyrolysis technique. The nanostructured SnO2 UV PDs were fabricated. The structural, optical, and surface morphological properties have been investigated using the characterizing techniques of XRD, UV, PL spectrophotometer, and FESEM, respectively. The growth mechanism of structural transformation from nanobranch (Nb) to nanorod (NR) structure was discussed extensively. The photoelectric properties of the fabricated devices were performed under UV light (365 nm wavelength). The PD devices responded to two bias voltage ranges of 0.0004 V and 0.5 V for Nb and NR devices, respectively. The reason behind its due to the influence of surface states in the material that has been explained. Based on the results, the as-fabricated devices detect low light intensity in the microwatt power range. The transient photoresponse profiles exhibit the abundant surface states formation in nanostructures which showed as persistent photocurrent. Quenching of photocurrent for NR PD was observed at 0.5 bias voltage. We attained large photosensitivity and low bias sensing ability of SnO2 PD devices which clearly indicate that the possibility of the development of environment monitor supported self-powered devices.

Design and construction of hierarchical Ni3S2 @V-doped NiMn-LDH heterostructure on rGO/Ni foam as an advanced electrode for battery-supercapacitor hybrid devices

Transition metal dopant engineering and rational architecture design have been proven to be effective strategies to improve the electrochemical energy storage properties of electrodes. Herein, V-doped NiMn-layered double hydroxide composites were supported on reduced graphene oxide-coated Ni foam (NMV-L/rGO) by a hydrothermal method. The influences of V content on the electrochemical performances of NMV-L/rGO composites were investigated in detail. At an optimal content of V doping (15%), the NMV-L/rGO-15 reveals enhanced electrochemical properties, and it is subsequently applied as the substrate for the electrodeposition of Ni3S2 layer. Benefiting from the collaborative effect of NMV-L/rGO-15, Ni3S2, and rGO materials, as well as the unique hierarchical architecture, excellent electrochemical performance is obtained in the as-prepared Ni3S2 @NMV-L/rGO-15 composite, which exhibits a high specific capacity of 1412.0 C g−1 at 1 A g−1 as well as desirable long-term stability of 89% over 5000 cycles. Furthermore, the as-fabricated battery-supercapacitor hybrid device (BSH) based on Ni3S2 @NMV-L/rGO-15 and activated carbon (AC) electrodes displays a remarkable energy density of 60.0 W h kg−1 at the power density of 849.1 W kg−1 and superior capacity retention of 96% through 7000 cycles. Such excellent results indicate that the Ni3S2 @NMV-L/rGO-15 composite holds great potential as electrode material for high-performance BSHs.

Preparation and electrochromic properties of flexible transparent WO3/AgNW-decorated nanofiber composite film

It is well-known that tungsten oxide (WO3) is extensively used for electrochromic (EC) devices due to its special properties, such as high coloration/bleaching response time, good coloration efficiency, etc. The preparation of flexible EC devices is highly desirable for various applications. However, the fabrication of flexible EC devices with improved performance is still a major task due to their limited experimental protocols. In this study, we have prepared highly flexible transparent films consisting of WO3 and silver nanowires coated on nanofiber-reinforced composite films (WO3/AgNW-NCF). A novel flexible transparent WO3/AgNW-NCF is used for EC applications. The as-fabricated EC device based on WO3/AgNW-NCF demonstrated good coloration efficiency (161.3 cm2 C−1), excellent stability (81.5%) and rapid response time for coloration (2.9 s) and bleaching (3.2 s). The fabricated transparent flexible EC device may potentially be useful for designing an outstanding EC device for smart window applications.

High-performance hybrid supercapacitors based on electrodeposited amorphous bimetallic nickel cobalt phosphide nanosheets

In this article, an amorphous bimetallic nickel cobalt phosphide (NiCoP) thin film composed of 2D nanosheets architecture was directly grown on Ni foam substrate by using one-step electrodeposition route and utilized as an efficient binder-free cathode for hybrid supercapacitors (HSCs). Particularly, the molar ratio of Ni/Co of the bimetallic NiCoP electrodes was systemically optimized for acquiring superior capacitive features. According to the synergistic advantages of ultrathin 2D nanosheets, good electrical conductivity of metal phosphides, and amorphous characteristics, the optimized bimetallic Ni0.5Co0.5P electrode exhibited the high specific capacity of 42.2 mA h g−1 at a current density of 1 A g−1, which was superior to the corresponding mono-metallic phosphides of NiP (38.8 mA h g−1) and CoP (21.5 mA h g−1). Moreover, an as-fabricated HSC device assembled with modified activated carbon anode and the Ni0.5Co0.5P cathode delivered not only an impressive specific capacity of 56.5 mA h g−1 at 1 A g−1, but also high energy density of 45.2 Wh kg−1 along with a power density of 800 W kg−1. Furthermore, the HSC device demonstrated good cycling stability with 86.7% capacity retention even after 10,000 cycles at 2 A g−1. Thereby, the facile and simple electrodeposition process and superior electrochemical performance of the electrodeposited NiCoP materials makes them as promising electrode materials for energy storage applications.

Amorphous V-doped Co3S4 yolk-shell hollow spheres derived from metal-organic framework for high-performance asymmetric supercapacitors

Metal-organic frameworks (MOFs) have appeared as a new option for constructing various functional materials for energy storage applications. In this work, a novel amorphous vanadium doped Co3S4 (V-CS) hollow sphere is synthesized through a facile method. Due to the unique structure, the amorphous V doped Co3S4 provides large amount of active sites for better storage energy. A remarkable specific capacitance of 1725 F g−1 at the current density of 0.3 A g−1 was achieved for this electrode. Further, the as-fabricated asymmetric supercapacitor device contains the V-CS electrode and activated carbon electrode (positive and negative, respectively) lead to outstanding performance with maximum energy and power densities of 88.29 Wh kg−1 and 486 W kg−1, respectively, that is better than traditional supercapacitors. In addition, the fabrication process illustrated in this article is facile, controllable, and economical, offering a viable method for fabricating the next generation of high-performance energy storage devices.

Full-Stokes Polarimeter Based on Chiral Perovskites with Chirality and Large Optical Anisotropy.

Full-Stokes polarimeters, equipped with the capability of discriminating light polarization states, can find important applications in various optical and optoelectronic devices. Nevertheless, currently most full-Stokes polarimeters require complex and bulky optical elements or optical metasystems integrated with metasurfaces, which can increase the cost and cause energy loss. Here, the anisotropy of chiral 2D perovskite single crystals is explored and the full-Stokes polarimeter based on pure chiral 2D perovskite single crystals is reported. By using optical anisotropy and the ability to distinguish the helicity of the circularly polarized light, chiral 2D perovskite polarimeter integrates the polarizer, waveplate, and photodetector together and thus can be able to discriminate the polarization states of light. The as-fabricated device exhibits a photoresponsivity of 0.136 A W-1 and a detectivity of 1.2 × 1010 Jones. This study provides a paradigm to construct filterless on-chip Stokes polarimeter with great simplicity and low cost.

Mitigating Ion Migration by Polyethylene Glycol-Modified Fullerene for Perovskite Solar Cells with Enhanced Stability

Ion migration, an intrinsic property that cannot be suppressed by device encapsulation, is of great importance to the long-term stability of perovskite solar cells. Herein, we synthesize a polyethylene glycol-modified fullerene (PCBHGE) and then incorporate it into perovskite absorber layers. It is found that PCBHGE can stabilize [PbI6]4– octahedral frameworks by forming Lewis acid–base pairs. Decoupling the efficient defect passivation of the fullerene core, ion migration is suppressed significantly in the as-fabricated devices. As a result, our state-of-the-art device demonstrates a highest efficiency of 23.19%. Most importantly, the device with PCBHGE can retain 87% of its maximum efficiency after 206 days. Tracked at the maximum power point under a continuous bias, the device efficiency hardly decreases in the first 212 h with a UV filter and can retain 80% of its initial efficiency after the next 600 h under full spectrum illumination including UV light.