Film-based Devices Research Articles

Improved Functionality of Ultrafast Responsive Electrochemiluminescent Device with DNA/Ru(bpy)3 2+ Hybrid Film and Various Electrolyte Compositions

Electrochemiluminescence (ECL), a light-emitting phenomenon induced by electrochemical redox reactions, has potential applications in lightweight and flexible light-emitting devices. Previously, an ultrafast ECL response of <100 μs was successfully achieved under application of alternating current voltage by using a DNA-modified electrode including Ru(bpy)3 2+, an orange ECL material. In this study, we investigated effect of electrolyte composition on the fast responsive ECL in the DNA/Ru(bpy)3 2+ hybrid film-based ECL device. As a result, the ECL intensity and lifetime of ECL were improved by introducing additional Ru(bpy)3 2+ into the electrolyte solution. The increase concentration of Ru(bpy)3 2+ inhibited dissolution of aggregated part formed on DNA/Ru(bpy)3 2+ hybrid film and increase in the amount of reactive charge in the aggregated part. Furthermore, we introduced blue-luminescent 9,10-diphenylanthracene (DPA) into the electrolyte solution of the ECL device consisting of DNA/Ru(bpy)3 2+ hybrid film. Consequently, blue ECL from DPA was obtained from the DNA/Ru(bpy)3 2+ hybrid electrode at lower applied voltage than that required to induce the redox reactions of DPA itself. This lower-voltage-drivable blue ECL was attributed to triplet–triplet energy transfer from Ru(bpy)3 2+ in the DNA/Ru(bpy)3 2+ hybrid electrode followed by a triplet–triplet annihilation upconversion reaction of DPA in the electrolyte solution. Moreover, ultrafast-response, electrochemically triggered blue luminescence from DPA was successfully observed.

Effect of annealing conditions on resistive switching in hafnium oxide-based MIM devices for low-power RRAM

Abstract This work presents resistive switching (RS) behaviour in HfO2-based low-power resistive random-access memory (RRAM) devices. A metal-insulator-metal (MIM) structure (Au/HfO2/Pt) was fabricated by sandwiching a thin insulating layer of HfO2 between Pt and Au electrodes. HfO2 films deposited by RF sputtering at room temperature were rapid thermally annealed in N2 ambient at 400 °C and 500 °C. Grazing angle x-ray diffraction (GIXRD), Field emission gun-scanning electron microscopy (FEG-SEM), atomic force microscopy (AFM), and x-ray photoelectron spectroscopy (XPS) were employed to analyse the phase, crystal structure, morphology, surface roughness and chemical composition of the HfO2 films. The bipolar RS could be observed in both as-deposited and annealed HfO2 film-based devices from I–V characteristics measured using a source meter. We have investigated the effect of annealing temperature and annealing ambient on the phase formation of HfO2 as well as the RS characteristics and compared with as-deposited film-based device. Annealed HfO2 film-based devices exhibited improved electrical characteristics, including stable and repeatable RS at significantly lower switching voltages (&lt;1 V) which indicates low power consumption in these devices. The relatively lower processing temperature of the HfO2 films and that too in the films deposited by physical vapor deposition (PVD) technique-RF magnetron sputtering makes this study significantly useful for resistive switching based non-volatile memories.

Single-crystal ferroelectric LiNbO3 thin film-based synaptic devices enabled with tunable domain wall current for neuromorphic computing

Neuromorphic devices can emulate the human brain to process information, which receives lots of attention in the field of artificial intelligence. Synaptic devices based on ferroelectric thin films feature low-power consumption, multifunctionality, and scalability. Among them, ferroelectric charged domain wall (CDW) devices have attracted intensive interest for the implementation of memristive devices due to their ultrahigh integration ability inherited from the nanoscale domain wall thickness. In particular, the preparation of wafer-scale single-crystalline ferroelectric thin films via ion-sliced heterogeneous wafer bonding lays a good foundation for large-scale integration of ferroelectric devices with functional circuits. However, the biomimic synaptic characteristics and the systematic demonstration of synaptic devices are largely unexplored for this material system. Here, we demonstrate a model synaptic device based on a single-crystal ferroelectric LiNbO3 thin film, which provides the desired characteristics for neuromorphic computing. The conductance modulation demonstrates good linearity for efficient neuromorphic computing applications. Simulations using the Modified National Institute of Standards and Technology handwritten recognition dataset prove that LiNbO3-based synaptic devices can operate with an online learning accuracy of 95.1%. The injection and annihilation of the CDW are proposed as the basis of the conductivity modulation by combining with the piezoresponse force microscopy and conductive atomic force microscopy mapping measurements. With the mature fabrication process of the ultrathin high-quality ferroelectric thin films, LiNbO3-based synaptic devices have an extensive application prospect for future neuromorphic computing systems.

Low-temperature growth of CuS thin film on flexible substrates for photodetection

Abstract The covellite phase of copper sulfide thin film (CuS), due to its excellent electronic, optical and chemical properties, has attracted enormous attention in cutting-edge research. This is a comprehensive study of the structural, optical, morphological and electrical properties of CuS thin films deposited by chemical bath deposition technique on flexible polyethylene terephthalate (PET) substrates at different deposition temperatures, i.e. 25 °C, 40 °C, 55 °C and 70 °C for the fabrication of flexible photodetectors. X-ray diffraction and Raman spectral studies reveal the presence of hexagonal covellite phase (CuS), whereas the root mean square (RMS) roughness of CuS thin film increases with an increase in deposition temperature. The optical bandgap of CuS thin film is found to be decreased with an increase in deposition temperature. The optimized CuS thin film, deposited at 70 °C, exhibits a homogeneous surface with RMS roughness of 13.72 nm, mobility of 25.09 cm2 V−1s−1 and bandgap of 1.86 eV. The mobility of CuS thin film is found to be increased with the increase in deposition temperature. The flexible CuS photodetector, fabricated at 70 °C, exhibits better photoresponse characteristics, with the highest responsivity of 0.18 mA W−1, specific detectivity of 1.39 × 108 Jones and sensitivity of 173.25 % upon light illumination. The established photocurrent possesses an outstanding dependence on various intensities of illuminated light. Furthermore, the bending test of flexible CuS photodetectors reveals the absence of any sign of deterioration up to bending angle of 30°. This suggests that the Al/CuS-PET/Al photodetector device could be used in various wearable optoelectronic device applications.

Time-Resolved Spatial Distributions of Individual Components of Electroactive Films during Potentiodynamic Electrodeposition.

Of the attributes that determine the performance of electroactive film-based devices, the least well quantified and understood is the spatial distribution of the component species. This is critical since it dictates the transport rates of all the mobile species (electrons, counterions, solvent, analyte, and reactant) and the film mechanical properties (as exploited in actuator devices). One of the few techniques able to provide individual species population profiles in situ is specular neutron reflectivity (NR). Historically, this information is obtained at the cost of poor time resolution (hours). Here we show how NR measurements with event mode data acquisition enable both spatial and temporal resolution; the latter can be selected postexperiment and varied during the transient. We profile individual species at "buried" interfaces under dynamic electrochemical conditions during polypyrrole electrodeposition and Cu deposition/dissolution. In the case of polypyrrole, the film is homogeneous throughout growth; there is no evidence of dendrite formation followed by solvent (water) displacement. Correlation of NR-derived film thickness and coulometric assay allows calculation of the solvent volume fraction, ϕS = 0.48. In the case of Cu in a deep eutectic solvent, the complexing nature of the medium results in time-dependent metal speciation: mechanistically, dissolution does not simply follow the deposition pathway in reverse.

Flexible thin-film thermoelectric generators for human skin-heat harvesting: A numerical study

By harvesting thermal energy from human skin, self-powered wearable electronics have the potential to overcome the limitations of battery power, enabling long-term continuous operation. Flexible thermoelectric generators (TEGs) that can form a conformal contact with heat sources of any shape are critical for self-powered wearables. Nevertheless, practical implementations and efficient harvesting of heat energy from the human body are still hindered by factors that significantly diminish the power output of flexible TEGs. In this work, we present a design framework and computational platform optimized for modelling the harvesting of skin-heat energy using organic-based flexible thin-film TEGs. First, a three-dimensional numerical model based on the finite element method (FEM) has been developed, which enables the study and optimization of organic-based film thermoelectric (TE) device and TEG parameters, such as width, length, thickness, and interconnection dimensions, to maximize performance. Then, the optimized flexible TEG has been used to investigate the effect of human skin on wearable device applications in different parts of the body and environmental conditions. Mechanical interlayers designed to control various interface functions can alter junction resistances, leading to structures that are either highly conductive or insulating. Soft heat conductor (SHC) and soft heat insulator (SHI) layers are embedded to enhance the thermal interfaces and temperature difference across the TEG. As a result, embedding these soft heat layers can increase the temperature difference (ΔT) and open circuit voltage (VOC) along the TEG by ∼30 % over conventional flexible thin-film TEGs, while preserving mechanical softness and flexibility. Additionally, a study on the impact of the skin/TEG matching and heat flux at the skin/TEG interface is presented. Lastly, using a state-of-the-art post-treated poly(3,4-ethylenedioxythiophene) polystyrene sulfonate (PEDOT:PSS) film-based TEG device model, we determined the maximum power output obtainable on various parts of the human body under three distinct environmental conditions (cold, room, and hot temperatures).

Harnessing ion beam erosion engineering for controlled self-assembly and tunable magnetic anisotropy in epitaxial films

The engineering of the surface morphology and the structure of the thin film is one of the essential technological assets for regulating the physical properties and functionalities of thin film-based devices. This study presents an easy and handy approach to tailor the surface structure of epitaxial thin films utilizing low-energy ion beam. Here, we investigate the evolution of the surface structure and magnetic anisotropy (MA) in epitaxial Fe/MgO (001) model systems subjected to multiple cycles of ion beam erosion (IBE) after thin film growth. The growth of Fe film occurs in the form of three–dimensional islands and exhibits intrinsic biaxial MA. Following a few cycles of IBE, an induced uniaxial magnetic anisotropy leads to a split in the hysteresis loop, and the film displays almost uniaxial magnetic switching behavior. More distinctly, we present a clear and conclusive evidence of (2 × 2) reconstruction of the Fe surface due to the atomic rearrangement by IBE. Furthermore, 57Fe isotope sensitive nuclear resonance scattering measurement provides insight into the depth-resolved magnetic information due to the modified surface topography. We also demonstrate that thermal annealing can reversibly tune the surface reconstruction and induced UMA. The feasibility of the IBE technique by adequately selecting IBE parameters for surface structure modification has been highlighted apart from conventional tailoring of the morphology for the tuning of UMA and introduces a new dimension to our understanding of self-assembled surface morphology evolution by IBE.

Cyanophenol and benzyl phosphonic acid grafted electrodes for poly(butyl viologen) thin film-based electrochromic device

Viologens are considered among the most promising electrochromic materials for utilization in electrochromic devices (ECDs). In this regard, poly(butyl viologen) (PBV) has gained interest due to its stability, conductivity, and ease of synthesis, thus making it suitable for electrochromic applications. Regrettably, the poor adhesion of PBV thin film with substrates/electrodes deters the redox properties and long-term stability of PBV-based ECDs. To address this issue, herein, two types of surface-modified indium tin oxide (ITO) electrodes, grafted with 4-cyanophenol (P–CN-ITO) and benzyl phosphonic acid (BPO3-ITO), are introduced for the deployment in PBV-based ECDs. The optical contrast (ΔT, %) for substrate-modified P–CN and BPO3-based ECD was measured to be ∼57.0 and ∼59.5, respectively, which was remarkably higher (an improvement of ∼66 %) than that of ECD with bare ITO (∼34.3). Meanwhile, the coloration times (τc) of the P–CN, BPO3, and bare ITO-based ECD were registered to be ∼1.7, ∼2.0, and ∼4.1 s, respectively, thus revealing the superiority of utilized functional groups over the unmodified substrate. The P–CN and BPO3-based ECD retained ∼70.2 % and ∼55.5 % of initial ΔT, respectively, after continuous switching of 10,000 cycles, thus showing high endurance and reversibility. The XPS results indicated the strong covalent bond formation between the utilized functional groups (P–CN and BPO3) and ITO, which delivered improved electrochemical, optical, and stability behavior when deployed in ECDs. Our study suggests that P–CN and BPO3-based substrates can be promising for deployment as terminal electrodes in viologen-based ECDs for improved overall performance.

Efficient Emission of Highly Polarized Thermal Radiation from a Suspended Aligned Carbon Nanotube Film.

A polarized light source covering a wide wavelength range is required in applications across diverse fields, including optical communication, photonics, spectroscopy, and imaging. For practical applications, high degrees of polarization and thermal performance are needed to ensure the stability of the radiation intensity and low energy consumption. Here, we achieved efficient emission of highly polarized and broadband thermal radiation from a suspended aligned carbon nanotube film. The anisotropic nature of the film, combined with the suspension, led to a high degree of linear polarization (∼0.9) and great thermal performance. Furthermore, we performed time-resolved measurements of thermal emission from the film, revealing a fast time response of approximately a few microseconds. We also obtained visible light emission from the device and analyzed the film's mechanical breakdown behavior to improve the emission intensity. Finally, we demonstrated that suspended devices with a constriction geometry can enhance the heating performance. These results show that carbon nanotube film-based devices, as electrically driven thermal emitters of polarized radiation, can play an important role for future development in optoelectronics and spectroscopy.

Nano-ZnO-Decorated lotus fibers for nonvolatile memristors

Electronic devices incorporating green materials offer a sustainable and environmentally friendly alternative, harnessing the unique properties of natural substances to contribute to a more eco-conscious and biodegradable technological landscape. This study extracts cellulose fibers from lotus petiole and decorates them with zinc oxide (ZnO) nanoparticles. The hybrid ZnO and cellulose (ZC) nanocomposite was used as a switching layer in the RRAM structure. The ZC thin film-based device displayed non-volatile bipolar behavior, whereas the device based on pure cellulose exhibited volatile behavior. This ZC-based device had significant enhancements, including a low operating voltage range of 2.0 V, a high ON/OFF resistance ratio of 103, endurance of 102 cycles, and an excellent retention time of 104 s. Oxygen vacancies, explored by PL and XPS results, are the most dominant in ZnO particles, indicating a substantial effect on the non-volatile characteristic in the Ag/ZC/FTO device. These results demonstrate that the lotus petiole cellulose-ZnO nanocomposite is a promising material for developing eco-friendly and low-cost memory devices.

Comprehensive study on pyrano[3,2-c]quinoline-based indole: Synthesis, characterization, and potential for optoelectronic and photovoltaic applications

The target indolylidenehydrazinylidenemethyl-pyrano[3,2-c]quinoline (IHMPQ) was synthesized and characterized. The DFT/ B3LYP approach using the 6–311++G(d,p) basis set was used to carry out the quantum computational calculations. The energy values of certain quantum chemical properties were calculated. The molecular electrostatic potential (MEP) and non-linear optical (NLO) characteristics are investigated. The Fukui function was used to forecast the reactive sites for electrophilic and nucleophilic attack using Mulliken population analysis. The calculated NMR chemical shifts were compared to experimental results. Furthermore, the study assessed the drug-likeness of the current compounds and discovered that they adhered to Lipinski's rule of five, making them appropriate for the development of oral drugs. Scanning electron microscopy was used to analyze the topography of the IHMPQ structure. The experimental results revealed a direct allowed energy gap, with values of 2.01 eV and 3.3 eV. Notably, IHMPQ films exhibit remarkable photoluminescence and absorption properties, suggesting their suitability for optoelectronic applications. Moreover, the investigation into the J-V characteristics of IHMPQ film-based devices under diverse illuminations unveiled a distinct response to incident light. This suggests the potential utility of these devices in solar cell applications.

Multilevel resistive switching in hydrothermally synthesized FeWO4 thin film-based memristive device for non-volatile memory application

The memristors offer significant advantages as a key element in non-volatile and brain-inspired neuromorphic systems because of their salient features such as remarkable endurance, ability to store multiple bits, fast operation speed, and extremely low energy usage. This work reports the resistive switching (RS) characteristics of the hydrothermally synthesized iron tungstate (FeWO4) based thin film memristive device. The detailed physicochemical analysis was investigated using Rietveld’s refinement, X-ray photoelectron spectroscopy (XPS), field emission scanning electron microscopy (FE-SEM), and transmission electron microscopy (TEM) techniques. The fabricated Ag/FWO/FTO memristive device exhibits bipolar resistive switching (BRS) behavior. In addition, the devices exhibit negative differential resistance (NDR) at both positive and negative bias. The charge-flux relation portrayed the non-ideal or memristive nature of the devices. The reliability in the RS process was analyzed in detail using Weibull distribution and time series analysis techniques. The device exhibits stable and multilevel endurance and retention characteristics which demonstrates the suitability of the device for the high-density non-volatile memory application. The current conduction of the device was dominated by Ohmic and trap controlled-space charge limited current (TC-SCLC) mechanisms and filamentary RS process responsible for the BRS in the device. In a nutshell, the present investigations reveal the potential use of the iron tungstate for the fabrication of memristive devices for the non-volatile memory application.

Investigating the effect of oxygen vacancy on electronic, optical, thermoelectric and thermodynamic properties of CeO2 (ceria) for energy and ReRAM applications: A first-principles quantum analysis

CeO2 thin film-based devices have become hot favorite candidates for researchers due to the outstanding characteristics of ceria such as memory storage materials, high oxygen storage capacity, excellent chemical and thermal stability, high transparency in visible region and highly tunable energy band structures. Developing suitable materials for industrial uses like optoelectronic and thermoelectric devices is the primary goal of researchers in the field of renewable energy. Herein, we have investigated the optical, thermoelectric and thermodynamic properties of CeO2 and [Formula: see text] as promising candidates for energy applications using first-principles calculations. We can observe significant absorption of incident photons by CeO2 and [Formula: see text] near UV region. The highest peaks of the [Formula: see text] are present around 3.7[Formula: see text]eV in spin [Formula: see text] channel, however, in spin [Formula: see text] channel, the highest peaks of the [Formula: see text] are present around 3.5[Formula: see text]eV. The most intense peaks that emerge are due to the transitions of O[[Formula: see text]] to Ce [[Formula: see text]]. The investigated values of [Formula: see text] reveal that CeO2 and [Formula: see text] are active optical materials. CeO2 and [Formula: see text] reflect a negligible number of incident photons ([Formula: see text]%) in the entire energy range. The positive value of the S shows that the CeO2 under study is p-type semiconductor, while [Formula: see text] is n-type semiconductor as its S value is negative. The S values for CeO2 are close to the established standard. As a result, CeO2 is a viable thermoelectric material for use in devices. The figure of merit (ZT) spectra reveals that CeO2 ([Formula: see text]) is a more capable candidate for thermoelectric materials compared to [Formula: see text] ([Formula: see text]). The investigated thermodynamic parameters reveal that CeO2 and [Formula: see text] are dynamically stable compounds.

Improved performance for Ag nanoparticles-assisted HfO2 thin film-based memcapacitive device

In this article, we have reported the deposition of Ag nanoparticles assisted HfO2 thin film-based device with an Au electrode using GLAD-assisted conventional electron beam evaporation technique for memcapacitive applications. The structural, morphology, and chemical compositions were investigated using XRD, FESEM, AFM, and XPS characteristics. The XPS analysis confirmed the presence of oxygen vacancy. The C-V hysteresis loop of the device at various sweeping voltages from ± 1 V to ± 4 V indicated the mechanism of trapping charges. The memory window of the device increased from 0.82 V to 2.21 V as well as the trapped charge density (N) increased from 6.81 × 109/cm2 to 18.35 × 109/cm2 with sweeping voltages increases from ± 1 V to ± 4 V. The C-V and G-V characteristic for different frequencies of 500 KHz to 1 MHz was conducted to investigate the charge-trapping nature of the device with a low interface trapped density (Dit) value of 8.82 × 1011 eV−1/ cm2 at 1 MHz. In addition, the deposited device exhibited forming-free abnormal bipolar resistive switching behavior with a charge conduction mechanism ascribed to hopping conduction and a strong space charge limited current (SCLC). Also, the device displayed a stable endurance of 2000 cycles, a resistance window of ∼252, and an excellent data retention of >104 s. These impressive results made the Ag nanoparticles-assisted HfO2 thin film a promising device for applications in advanced memcapacitive non-volatile memory technologies for the next generation.

Improving device performance of sputtered CZTSe based solar cells by Manganese doping

Despite many efforts, Cu2ZnSnSe4 (CZTSe) based solar cells have remained relatively low efficiency compared to other thin film-based devices. One of the prevalent strategies used to improve cell performance in CZTSe is cation substitution. In this contribution, the effects of substituting Mn for Zn on CZTSe solar cell performance were systematically examined. Samples with various Mn content were grown by a two-stage method involving high temperature annealing of precursor layers comprising Cu, Zn, Sn, Mn and Se. All of the samples were found to have Cu-poor and (Zn + Mn)-rich or nearly stoichometric compositions. They crystalized in kesterite phase irrespective of the Mn content as confirmed by X-ray diffraction (XRD), Raman and X-ray photoelectron spectroscopy (XPS) measurements. The highest efficiency solar cell (5.56%) was obtained employing the 5% Mn doped CZTSe absorber. This film was found to have improved microstructure and reduced defect density. This is the first report on over 5% efficient kesterite thin film solar cell fabricated on a Cu2Mn0.05Zn0.95SnSe4absorber layer.

All-Automated Fabrication of Freestanding and Scalable Photo-Thermoelectric Devices with High Performance.

Flexible photo-thermoelectric (PTE) devices have great application prospects in the fields of solar energy conversion, ultrabroadband light detection, etc. A suitable manufacturing process to avoid the substrate effects as well as to create a narrow transition area between p-n modules for high-performance freestanding flexible PTE devices is highly desired. Herein, an automated laser fabrication (ALF) method is reported to construct the PTE devices with rylene-diimide-doped n-type single-walled carbon nanotube (SWCNT) films. Thewet-compressing approach is developed to improve the thermoelectric power factors and figure of merit (ZT) of the SWCNT hybrid films. Then, the films are cut and patterned automatically to make PTE devices with various structures by the proposed ALF method. The freestanding PTE device with a narrow transition area of ≈2-3 µm between the p and n modules exhibits a high-power density of 0.32 µW cm-2 under the light of 200 mW cm-2, which is among the highest level for freestanding-film-based PTE devices. The results pave the way for the automatic production process of PTE devices for green power generation and ultrabroadband light detection.

Controllable Circularly Polarized Luminescence with High Dissymmetry Factor via Co-Assembly of Achiral Dyes in Liquid Crystal Polymer Films.

Circularly polarized luminescence (CPL) materials are highly demanded due to their great potential in optoelectronic and chiroptical elements. However, the preparation of CPL films with high luminescence dissymmetry factors (glum) remains a formidable task, which impedes their practical application in film-based devices. Herein, a facile strategy to prepare solid CPL film with a high glum through exogenous chiral induction and amplification of liquid crystal polymers is proposed. Amplification and reversion of the CPL appear when the films are annealed at the chiral nematic liquid crystalline temperature and the maximal glum up to 0.30 due to the enhancement of selective reflection. Thermal annealing treatment at different liquid crystalline states facilitates the formation of the chiral liquid phase and adjusts the circularly polarized emission. This work not only provides a straightforward and versatile platform to construct organic films capable of exhibiting strong circularly polarized emission but also is helpful in understanding the exact mechanism for the liquid crystal enhancement of CPL performance.

Suppression of Randomness in Electrically Pumped Random Lasing from a ZnO Film-Based Light-Emitting Device on Silicon.

We report on the suppressed randomness in electrically pumped random lasing (RL) from a light-emitting device (LED) based on a metal-insulator-semiconductor (MIS) structure of Au/SiOx (x < 2)/ZnO on a silicon substrate, by means of patterning the light-emitting ZnO polycrystalline film into a number of square blocks separated by streets that are filled with the SiOx insulator. It is found that the RL modes can be remarkably reduced by shrinking the blocks in the absence of interblock optical coupling. Meanwhile, with the imposition of interblock optical coupling by shrinking the streets, the RL modes can be further reduced, and more importantly, the strongest mode wavelength is stabilized around 380 nm, where the ZnO film exhibits the largest optical gain.

Laser-induced graphene-based digital microfluidics (gDMF): a versatile platform with sub-one-dollar cost.

Digital microfluidics (DMF), is an emerging liquid-handling technology, that shows promising potential in various biological and biomedical applications. However, the fabrication of conventional DMF chips is usually complicated, time-consuming, and costly, which seriously limits their widespread applications, especially in the field of point-of-care testing (POCT). Although the paper- or film-based DMF devices can offer an inexpensive and convenient alternative, they still suffer from the planar addressing structure, and thus, limited electrode quantity. To address the above issues, we herein describe the development of a laser-induced graphene (LIG) based digital microfluidics chip (gDMF). It can be easily made (within 10 min, under ambient conditions, without the need of costly materials or cleanroom-based techniques) by a computer-controlled laser scribing process. Moreover, both the planar addressing DMF (pgDMF) and vertical addressing DMF (vgDMF) can be readily achieved, with the latter offering the potential of a higher electrode density. Also, both of them have an impressively low cost of below $1 ($0.85 for pgDMF, $0.59 for vgDMF). Experiments also show that both pgDMF and vgDMF have a comparable performance to conventional DMF devices, with a colorimetric assay performed on vgDMF as proof-of-concept to demonstrate their applicability. Given the simple fabrication, low cost, full function, and the ease of modifying the electrode pattern for various applications, it is reasonably expect that the proposed gDMF may offer an alternative choice as a versatile platform for POCT.

Observation of piezoelectricity in a lead-free Cs2AgBiBr6 perovskite: a new entrant in the energy harvesting arena.

Halide perovskite materials have recently been recognised as powerful ferroelectric and piezoelectric materials with applications in the energy harvesting arena, but their experimental proof is very limited. We achieved strong intrinsic piezoelectricity in the lead-free inorganic double perovskite Cs2AgBiBr6 at room temperature and utilized it for mechanical energy harvesting, with a piezoelectric co-efficient (d33) of 12.7 pC N-1. Hysteresis loop and structural analyses offered further validation for the substantial ferroelectric features of the as-synthesised double perovskite. Density functional theory (DFT) calculations revealed the presence of anharmonic phonon soft modes in tetragonal Cs2AgBiBr6 due to dynamic instability, which resulted in piezoelectricity. Under an optimal pressure of ≈25 kPa, a Cs2AgBiBr6 thin film-based piezoelectric nanogenerator device delivered instantaneous output values of ≈45 V and ≈200 nA. The strain-sensitive responses of the device were also exemplified to identify specific body motions from the detected instantaneous output values. The energy obtained from the device is shown to be effective for capacitor charging and commercial light-emitting diode (LED) lighting. Our study provides significant insights into the dielectric behaviour of materials as well as piezo- and ferroelectric behaviours, which are crucial for the development of modern electronic and energy harvesting devices.