Encapsulation Layer Research Articles

P‐50: Inkjet Printing Design and Analysis for Thin and Uniform Organic Encapsulation Layer on OLEDs

This study focuses at the efforts to realize thin and uniform organic encapsulation layer in OLED. Controlling the drop accuracy and the volume size is a necessary process in this research. By using new inkjet process approaches, we obtained the best printing properties of thin film encapsulation (TFE).

Flexible core-sheath thermochromic phase change fibers for temperature management and electrical/solar energy harvesting

As clean and repeatable thermal energy storage materials, phase change materials (PCMs) exhibit excellent capability in absorption and releasing latent heat for thermal energy storage and thermal management applications. Integrating PCMs in flexible fibers provides new strategy for smart wearable systems. However, though lots of efforts have been made, it is still challenging to design and fabricate phase change fibers with flexibility, high energy storage capacity and good shape stability. Herein, we present a wet-spinning based core-sheath strategy to fabricate smart thermochromic phase change fibers (TPCFs) by directly encapsulating PCMs into flexible fibers in a low-cost, fast and adjustable way using octadecane (OD) as core, PCMs and polyurethane (PU) with thermochromic microcapsules as encapsulation layer. The obtained TPCFs exhibited high enthalpy (185 J/g), excellent mechanical property (elongation of 800%), thermal stability and reliability, outstanding shape stability and temperature responsiveness. Moreover, the materials possess high electrical-thermal and solar-thermal conversion and storage efficiency of 90.2% and 91.4% respectively through integrating with carbon fibers. These attractive features make TPCFs potential materials for wearable thermal management and energy harvesting and storage applications.

Investigation on Parylene-C based neural electrodes by accelerated life test and reliability improvement using polyimide flexible cable

Since the encapsulation layer of the neural electrode plays an important role in determining the reliability of the device, more studies on the long-term reliability of Parylene-C are required. In this paper, we described the long-term reliability of Parylene-C based neural electrodes through an accelerated lift test and proposed a method to improve the reliability using polyimide flexible cable (PFC) attached to the Parylene-C device. The accelerated lifetime test was performed in phosphate-buffered saline at 50 °C. The electrochemical characteristics were acquired and analyzed to evaluate the reliability of the Parylene-C coated neural electrode for up to 56 days, which is equivalent to 115 days as an accelerated time. The proposed PFC method showed improved long-term stability of the device, demonstrating an increased lifetime, showing that testing conditions and device setup affect overall results. This study will help make reliable Parylene-C based neural electrode systems with improved moisture protection.

Excellent Stability of Perovskite Solar Cells Encapsulated With Paraffin/Ethylene-Vinyl Acetate/Paraffin Composite Layer

Superior encapsulation technology is important for PSCs to prolong their lifetime and realize their commercial application. Paraffin/EVA/paraffin composite encapsulated layers were fabricated with the ambient environment under the thermal temperature of 80°C, which has advantages for simple procedures and low cost. PSCs encapsulated with paraffin/EVA/paraffin and pure EVA layers maintained 95 and 45% of the initial power conversion efficiency (PCE) aged for 1000 h at RH 75%, respectively. Paraffin/EVA/paraffin-encapsulated PSCs were immersed in water for 5 h, which remained 98% of the original PCE, which is far superior to EVA-encapsulated PSCs. High melting point paraffin at 68°C shows better encapsulation than low melting point (60 and 55°C) paraffin, indicating that the high molecular weight of paraffin helps improve the encapsulation performance of PSCs. PSCs encapsulated with paraffin/EVA/paraffin showed better stability of Voc than pure EVA layer because paraffin can inhibit defects, voids, and edges of metal electrodes that quickly expand, and decay. Therefore, paraffin/EVA/paraffin combination encapsulation is an effective strategy, which can form continuous and dense hydrophobic composite encapsulation films with a friendly metal electrode.

Stable Al2O3 Encapsulation of MoS2‐FETs Enabled by CVD Grown h‐BN

AbstractMolybdenum disulfide (MoS2) has great potential as a two‐dimensional semiconductor for electronic and optoelectronic application, but its high sensitivity to environmental adsorbents and charge transfer from neighboring dielectrics can lead to device variability and instability. Aluminum oxide (Al2O3) is widely used as an encapsulation layer in (opto)‐electronics, but it leads to detrimental charge transfer n‐doping to MoS2. Here, this work reports a scalable encapsulation approach for MoS2 field‐effect transistors (FETs) where hexagonal boron nitride (h‐BN) monolayers are employed as a barrier layer in‐between each of the Al2O3 and MoS2 interfaces. These devices exhibit a significant reduction of charge transfer, when compared to structures without h‐BN. This benefit of h‐BN in the gate stack is confirmed by ab initio density functional theory calculations. In addition, the devices with h‐BN layers show very low hysteresis even under ambient operating conditions.

A high-performance, single-electrode and stretchable piezo-triboelectric hybrid patch for omnidirectional biomechanical energy harvesting and motion monitoring

Triboelectric nanogenerators (TENGs) have recently drawn much attention in the field of biomechanical energy harvesting and motion monitoring. However, the electrode stretchability and contact-separation model induced complicated packed structure remain a problem that heavily affects output performance during various human movements and requires to be urgently addressed. Here, a single-electrode piezo-triboelectric hybrid nanogenerator (SEP-TENG) integrated with stretchable liquid-metal metal electrodes is reported, which simultaneously achieves outstanding energy harvesting performance and skin-comfort human motion monitoring. A polarized piezoelectric BaTiO3/silicon rubber (SR) composites film is served as the effective negative tribomaterial, benefiting from the improved dielectric constant and piezoelectric charge transfer, the optimized SEP-TENG generates a high peak power density of 5.7 W/m2 while contacted with human skin. Besides, owing to the ultralow Young's modulus of the SR encapsulation layer and tribo-piezoelectric hybrid layer, the homogeneous integrated multilayer composite serves no break till a 745% elongation, promoting that the SEP-TENG could effectively harvest biomechanical energy and realize stable power supplying for wearable electronics even under large deformation state. Furthermore, the SEP-TENG could comfortably attach to the finger joints and collect bending energy. This work provides a novel design methodology for a single-electrode TENG to realize omnidirectional biomechanical energy harvesting and motion monitoring.

Functional Encapsulating Structure for Wireless and Immediate Monitoring of the Fluid Penetration

AbstractWith the fast‐paced development of biomedical electronics, monitoring physiological processes have become ubiquitous throughout the field of implantable devices. Nevertheless, inherent challenges remain extant when long‐term applications are concerned. For the stable and reliable function of these devices, hermetic and biocompatible encapsulation is of paramount importance; however, extrinsic defects and intrinsic swelling properties of the encapsulating layer present the key limitation to ideal barrier performance. Thus, the ability to monitor biofluid penetration and predict the device's functional lifespan is necessary for safe and stable operation within the body. This paper presents the functional encapsulation structure that quantitatively measures the diffusion of fluids into the encapsulation layer. The hydrolysis of Magnesium (Mg) electrodes underneath the encapsulating material shows the capability to wirelessly monitor the water penetration rate and the presence of defects, such as pinholes and cracks, in the encapsulating material. The experiments conducted throughout this paper analyze the Mg thickness and geometry of the antenna to optimize the device's susceptivity to water penetration when submerged in aqueous environments. The facile fabrication process and the compatibility with prevailing implantable electronics further substantiate the device's usability in diverse applications where chronic implants are necessary for monitoring disease or administering required treatments.

Amplified spontaneous emission of perovskite in water: Towards under-water lasing

The application of halide perovskite materials as lasing devices has recently attracted great attention. However, the instability of such materials against moisture significantly restrict the application in many occasions. In order to protect the unstable perovskite materials against oxygen and moisture, various encapsulation strategies have been proposed. Regrettably, few of them are designed for aqueous environments. Herein, we demonstrate a photo-polymerized acrylic acid (ADCP) acting as substrate and encapsulation layer to fabricate (CH3NH3)PbBr3 (MAPbBr3) films and realize amplified spontaneous emission (ASE) with low threshold in water. Lasing threshold from MAPbBr3 films sandwiched by ADCP decreases slightly from 12 μJ/cm2 in air to ∼9 μJ/cm2 in water. The specific morphology, superb wettability and high-water stability are expected to contribute to the low ASE threshold. The aqueous environment with higher refractive index is speculated to be one of the origins of the slightly lower ASE threshold. Our results demonstrate a strong potential for applications of perovskite materials in lasing devices in aqueous environment and a new path to realize low threshold lasing.

Hyperbranched phthalocyanine enabling black-phase formamidinium perovskite solar cells processing and operating in humidity open air

The extreme instability of pure α-phase FAPbI3 under high humidity conditions restricts the high-throughput fabrication in unmodified air environments, resulting in poor performance of α-phase FAPbI3 perovskite devices obtained by scalable fabrication methods. Here we synthesized hyperbranched copper phthalocyanine (HCuPc) as a supramolecular additive with twisted phthalocyanine units to realize the molecular-level encapsulation at the grain boundaries through supramolecular interaction, which greatly broadened the processing window of FAPbI3 under high humidity. At the same time, unlike traditional encapsulation layer that carrier can only be collected by tunneling effect, the twisted phthalocyanine ring of HCuPc in perovskite films is more conducive to hole extraction. Finally, a record efficiency was achieved in pure FAPbI3 based inverted structured solar cell by blade-coating to the best of our knowledge, even under unmodified humid air conditions (relative humidity of 65%–85%). The best operational stability of 3D pure FAPbI3 devices can also be achieved at the same time and unencapsulated HCuPc-FAPbI3 device can even operate with negligible degradation for 100 h in the open air (RH 30%–40%).

Ultrathin encapsulated rGO strain sensor for gesture recognition

As an important component of wearable devices, strain sensors have attracted extensive attention. Usually, the exposed strain sensors have better gauge factor (GF) but a small strain range. Encapsulation can increase the strain range, but the influence of the encapsulation on device performance remains elusive. In this work, we proposed a reduced graphene oxide (rGO) strain sensor based on ultrathin polyurethane (PU) encapsulation layer. The maximum strain range of single-layer encapsulated PU-based rGO strain sensor (PGSS) can reach 51%, and its GF is between 8.02 and 125.05. In addition, we explored the effect of thickness of encapsulated layer on the performance of PGSS. For the strain-resistance change rate curve, within the same strain range, the PGSS with thinner encapsulation layer is more sensitive to force. Furthermore, a smart glove based on PGSS was developed, which can effectively distinguish ten different gestures. This work has high potential in the fields of physiological signal monitoring and human-machine interaction.

Design of hybrid MoS2/photonic devices compatible with technological constraints

The integration of transition metal dichalcogenide layers into photonic devices is a current challenge in the field of 2D materials. Based on numerical simulations, this work explores the design of devices combining an MoS2 monolayer with planar photonic gratings sustaining localized optical resonances. A special attention is paid to the technological constraints. The optical response of six devices is compared taking into account the limitations imposed by the growth conditions of the MoS2 layer and the processing of the resonant optical gratings. The reported photonic devices composed of grating filters and a backside reflector on silicon and silica substrates exhibit a theoretical absorption by the MoS2 layer between 85 and 99% at 532 nm. The numerical simulations further show that the addition of an Al2O3 encapsulation layer, to protect the MoS2 monolayer, results in an increase of the performance of the devices. These hybrid MoS2 based photonic devices are promising technological platforms for the study of the optical properties of integrated MoS2 monolayers.

Ohmic contact formation to GaN by Ge+ implantation doping: Implantation fluence and encapsulation layer studies

This work investigates aspects of electrical doping of gallium nitride (GaN) by Ge+ ion implantation for low-resistivity ohmic contacts, with particular emphasis on reducing the level of defects produced. The 250 keV Ge+ ions were implanted through a retarding layer, with different effective fluences (2.4 × 1015–8.8 × 1015 cm−2), while dopant activation was done at a moderate temperature of 1100 °C using different encapsulation layers. Structural and electrical studies were performed: optical microscopy, Rutherford backscattering spectrometry in channeling geometry (with detailed analysis of point and extended defects using the McChasy software), and circular Transfer Line Method measurements were used. Implantation with the effective fluence of 4.8 × 1015 cm−2 allowed the formation of ohmic contacts with a specific contact resistance of (0.60 ± 0.07) Ω·mm while GaN sheet resistivity was (499 ± 15) Ω/sq., while implantations with both lower and higher fluences produced worse contacts. The topSiO2/AlN bilayer proved to be the best encapsulation layer, offering protection from surface degradation, good electrical parameters, and reproducibility. Although Ge+ implantation doping is promising, potentially introducing more dopants than respective Si+ doping, its drawback could be the higher concentrations of defects formed, thus damage prevention and removal (during both the implantation and activation annealing) is crucial.

Multifunctional nanostructured host-guest POM@MOF with lead sequestration capability induced stable and efficient perovskite solar cells

Long term stability and the toxicity of leaked lead ions represent the main barriers for commercialization of perovskite solar cells (PSCs). Here we report a novel chemical doping strategy with a series of polyoxometalates-metal organic frameworks (P@Ms) host-guest nanostructured dopants, shattering those barriers while maintaining a high-power conversion efficiency (PCE). The controllably oxidation of Spiro-OMeTAD was achieved under an inert environment through regulating the mass loading of H3PMo12O40 in a porphyrin-based MOF-545. Furthermore, the doped devices show a high PCE (21.5%) with remarkable long-term air stability, retaining approximately 85% of the initial PCE value for over 1000 h in ambient conditions. Significantly, the functionalized P@M with active sites as an encapsulation layer effectively restrict the migration and leakage of Pb2+ from the degraded PSCs, preventing the possible heavy metal pollution. This efficient strategy addresses the main troublesome long-term stability and lead ions leakage issues simultaneously, yielding stable and environmental-friendly sustainable PSCs.

Magnetotransport Studies of Encapsulated Topological Insulator Bi2Se3 Nanoribbons.

The majority of proposed exotic applications employing 3D topological insulators require high-quality materials with reduced dimensions. Catalyst-free, PVD-grown Bi2Se3 nanoribbons are particularly promising for these applications due to the extraordinarily high mobility of their surface Dirac states, and low bulk carrier densities. However, these materials are prone to the formation of surface accumulation layers; therefore, the implementation of surface encapsulation layers and the choice of appropriate dielectrics for building gate-tunable devices are important. In this work, all-around ZnO-encapsulated nanoribbons are investigated. Gate-dependent magnetotransport measurements show improved charge transport characteristics as reduced nanoribbon/substrate interface carrier densities compared to the values obtained for the as-grown nanoribbons on SiO2 substrates.

Aging behaviour of encapsulated assemblies of epoxy resin under accelerated thermal cycling

Epoxy potting materials are inevitably exposed to cyclic temperature environments during use. Under temperature load, thermal stress concentration occurs inside the epoxy encapsulation layer and leads to interface debonding and resin cracking, which eventually leads to the failure of the encapsulated component. In view of this, the effects of thermal cycling on epoxy resin and its encapsulated assemblies were investigated in this work. The surface morphology was characterized by scanning electron microscope (SEM) and atomic force microscope (AFM), the mechanical properties were measured by the Shore hardness tester and universal electronic extensometer, and the differential scanning calorimetry (DSC) and thermogravimetric analysis (TGA) were employed to explore the thermogravimetric and thermal stability of epoxy resin under thermal cycling. The electrical properties of encapsulated assemblies of epoxy resin were measured by broadband dielectric spectroscopy and breakdown voltage. Fourier-transform infrared spectroscopy (FTIR) and X-ray photoelectron spectroscopy (XPS) were used to characterize the changes of the epoxy molecular structure before and after thermal cycling. Based on the aforementioned results and analysis, an aging mechanism of epoxy resin under an alternating thermal cycle was proposed.

Ray-optics study of gentle non-conformal texture morphologies for perovskite/silicon tandems.

We investigate gentle front side textures for perovskite/silicon tandem solar cells. These textures enhance the absorption of sunlight, yet are sufficiently gentle to allow deposition of an efficient perovskite top cell. We present a tandem solar cell with such gentle texture, fabricated by Kaneka corporation, with an efficiency as high as 28.6%. We perform an extensive ray-optics study, exploring non-conformal textures at the front and rear side of the perovskite layer. Our results reveal that a gentle texture with steepness of only 23° can be more optically efficient than conventional textures with more than double that steepness. We also show that the observed anti-reflective effect of such gentle textures is not based a double bounce, but on light trapping by total internal reflection. As a result, the optical effects of the encapsulation layers play an important role, and have to be accounted for when evaluating the texture design for perovskite/silicon tandems.

Photothermal trap with multi-scale micro-nano hierarchical structure enhances light absorption and promote photothermal anti-icing/deicing

Facing climate change caused by carbon emissions and the disaster of ice accumulation on outdoor equipment, the large-scale use of solar energy is a promising solution. Here, a photothermal anti-icing material composed of substrate, carbon-based light-absorption layer, and encapsulation layer was prepared using a combined template-spraying method. The multi-scale micro-nano hierarchical structure can enhance light absorption in a limited space due to the light trapping effect, which was confirmed by ray-tracing simulation and the UV–vis-NIR light absorption result, and the average light absorption rate is up to ∼ 98% at the 200–2000 nm wavelength. The average surface temperature can reach ∼ 85 °C under 1 sun (qi = 100 mW/cm2) illumination at room temperature (Tr = 25 °C), and the photo-to-thermal conversion efficiency is up to 60.76%. Excellent photothermal conversion performance endows the material with the ability of photothermal deicing, and the frost or ice layer can melt and fall off from the surface after 300 s of 1 sun illumination. Besides, the photothermal anti-icing experiments under 1 sun illumination show that the prepared material has a lower freezing temperature (-25.20 ± 1.34 °C), a longer freezing delay time (774.76 ± 114.19 s), and a heat transfer model during the icing process was proposed. Surface friction, water flow impact, and solution immersion tests show that the material has excellent mechanical durability and chemical stability. The materials prepared in this work show enormous application potential on outdoor equipment due to the simple preparation method, strong mechanical durability, and excellent photothermal anti-icing/deicing properties.

Hierarchical conformal coating enables highly stable microparticle Si anodes for advanced Li-ion batteries

Microsized silicon powders have great potential for high capacity anode materials in next-generation lithium ion batteries, because of the high gravimetric and volumetric energy densities, ease of mass production and low costs. However, large volume change and consequently rapid capacity fading upon lithiation and delithiation prevent its practical applications. Herein, we demonstrate an effective hierarchical conformal coating strategy for high-performance microsized Si anodes. The Si-based composites consist of an amorphous Li-Si-O inner coating layer and a graphene outer encapsulation layer, which are prepared by coupling reactive milling with electrostatic self-assembly. This unique hierarchical conformal coating structure not only strengthens the mechanical property (31.8 GPa for the elastic modulus) and promotes the ionic diffusion (2.03 × 10−10 cm2 s−1) of Si anode, but also effectively stabilizes the electrode/electrolyte interfaces and increases the electronic conductivity. As a result, a high reversible capacity (1450 mA⋅h g−1 at 0.1 A g−1), good cycling stability (97.7% of capacity retention from the 2nd to the 310th cycle at 0.5 A g−1), and high rate capability (703 mA⋅h g−1 at 5 A g−1) have been successfully achieved. These findings provide new insights into the improvement of electrochemical properties of microsized Si composite anodes for high-performance Li-ion batteries.

A facile approach to fabricate flexible capacitance sensor based onSpatial Confining Forced Network Assemblymethod for detecting and analyzing large deformation of damping rubber

AbstractEfficiently estimating the aging status of rubber damping is indispensable in the transport system. Herein, we developed a facile approach to fabricate flexible capacitance sensors that can bear high loads, large deformations, and long cycle life. The sensor has a sandwich structure, including electrode layer, the dielectric layer, and encapsulation layer. In this approach, the spatial confining forced network assembly method was used to fabricate the electrode layer of the sensor and a novel injection mold process was used to form the encapsulation layer of the sensor. This flexible capacitive sensor can detect the cyclic loading of damping rubber springs as high as 0‐60 kN under load frequency of 3 Hz with a sensitivity of 30 PF/KN, bear up to maximum 58% deformation and cycling stability over 50,000 cycle. Furthermore, a modified aging status prediction model for damping rubber springs based on the signal of sensor is proposed. The real‐time working state and aging state of the rubber spring can be monitored through the measurement signal of the sensor.

Oxynitride-Encapsulated Silver Nanowire Transparent Electrode with Enhanced Thermal, Electrical, and Chemical Stability.

Silver nanowire (AgNW) networks have been explored as a promising technology for transparent electrodes due to their solution-processability, low-cost implementation, and excellent trade-off between sheet resistance and transparency. However, their large-scale implementation in applications such as solar cells, transparent heaters, and display applications has been hindered by their poor thermal, electrical, and chemical stability. In this work, we present reactive sputtering as a method for fast deposition of metal oxynitrides as an encapsulant layer on AgNWs. Because O2 cannot be used as a reactive gas in the presence of oxidation-sensitive materials such as Ag, N2 is used under moderate sputtering base pressures to leverage residual H2O on the sample and chamber to deposit Al, Ti, and Zr oxynitrides (AlOxNy, TiOxNy, and ZrOxNy) on Ag nanowires on glass and polymer substrates. All encapsulants improve AgNW networks' electrical, thermal, and chemical stability. In particular, AlOxNy-encapsulated networks present exceptional chemical stability (negligible increase in resistance over 7 days at 80% relative humidity and 80 °C) and transparency (96% for 20 nm films on AgNWs), while TiOxNy demonstrates exceptional thermal and electrical stability (stability up to over temperatures 100 °C more than that of bare AgNW networks, with a maximum areal power density of 1.72 W/cm2, and no resistance divergence at up to 20 V), and ZrOxNy presents intermediate properties in all metrics. In summary, a novel method of oxynitride deposition, leveraging moderate base pressure reactive sputtering, is demonstrated for AgNW encapsulant deposition, which is compatible with roll-to-roll processes that are operated at commercial scales, and this technique can be extended to arbitrary, vacuum-compatible substrates and device architectures.