Hybrid Thin Film Encapsulation for Improving the Stability of PbS Quantum Dot Solar Cells.

The instability to moisture, heat, and ultraviolet (UV) light is the main problem in the application of quantum dot solar cells (QDSCs). Thin film encapsulation can effectively improve their operational stability. However, it is difficult to achieve multiple barrier effects with single layer of encapsulated film. Here, a hybrid thin-film encapsulation strategy is reported to encapsulate lead sulfide QDSCs, which can isolate moisture and partial thermal, and prevent the penetration of UV light, thus retarding the surface oxidation process of the quantum dots. After 60 h, the encapsulated device retains a normalized power conversion efficiency of 83.8% and 80.6% at 85% humidity and 75 °C, respectively, which is three and six times of the value obtained in unencapsulated devices. At continuous UV illumination, encapsulated device exhibits five times higher stability than the reference. This strategy provides the way for the overall improvement of the operating stability of lead sulfide QDSCs in harsh environments of high humidity, high temperature, and UV light.

Advancements in atomic-scale interface engineering for flexible electronics: enhancing flexibility and durability.

Flexible electronics, such as wearable displays, implantable electronics, soft robots, and smart skin, have garnered increasing attention. Despite notable advancements in research, a bottleneck remains at the product level due to the prevalent use of polymer-based materials, requiring encapsulation films for lifespan extension and reliable performance. Multilayer composites, incorporating thin inorganic layers to maintain low permeability towards moisture, oxygen, ions, etc, exhibit potential in achieving highly flexible barriers but encounter challenges stemming from interface instability between layers. This perspective offers a succinct review of strategies and provides atomic-scale interface modulation strategy utilizing atomic layer integration technology focused on enhancing the flexibility of high-barrier films. It delves into bendable multilayers with atomic-scale interface modulation strategies, encompassing internal stress and applied stress modulation, as well as stretchable composite structural designs such as gradient/hybrid, wavy, and island. These strategies showcase significant improvements in flexibility from bendable to stretchable while maintaining high barrier properties. Besides, optimized manufacturing methods, materials, and complex structure design based on atomic-scale interface engineering are provided, better aligning with the future development of flexible electronics. By laying the groundwork for these atomic-scale strategies, this perspective contributes to the evolution of flexible electronics, enhancing their flexibility, durability, and functionality.

A Solvent-Free, Thermally Curable Low-Temperature Organic Planarization Layer for Thin Film Encapsulation.

Thin film encapsulation (TFE) is an essential component to ensure reliable operation of environmentally susceptible organic light-emitting diode-based display. In order to integrate defect-free TFE on display with complex surface structures, additional planarization layer is imperative to planarize the surface topography. The thickness of conventional planarization layer is as high as tens of µm, but the thickness must be reduced substantially to minimize the light leakage in smaller devices such as micro light-emitting diodes. In this study, a thin-less than 2 µm-planarization is achieved via solvent-free process, initiated chemical vapor deposition (iCVD). By adapting copolymer from two soft, but curable monomers, glycidyl acrylate (GA) and 2-(dimethylamino)ethyl methacrylate, excellent planarization performance is achieved on various nano-grating patterns. With only 1.5 µm-thick iCVD planarization layer, a 600 nm-deep trench polyurethane acrylate pattern is flattened completely. The TFE fabricated on planarized pattern exhibits excellent barrier property as fabricated on flat glass substrate, which strongly suggests that iCVD planarization layer can serve as a promising planarization layer to fabricate TFE on various types of complicated device surfaces.

Effect of different oxygen precursors on alumina deposited using a spatial atomic layer deposition system for thin-film encapsulation of perovskite solar cells.

An atmospheric-pressure spatial atomic layer deposition system operated in atmospheric-pressure spatial chemical vapor deposition conditions is employed to deposit alumina (AlOx) thin films using trimethylaluminum and different oxidants, including water (H2O), hydrogen peroxide (H2O2), and ozone (O3). The impact of the oxygen precursor on the structural properties of the films and their moisture-barrier performance is investigated. The O3-AlOxfilms, followed by H2O2-AlOx, exhibit higher refractive indexes, lower concentrations of OH- groups, and lower water-vapor-transmission rates compared to the films deposited using water (H2O-AlOx). The AlOxfilms are then rapidly deposited as thin-film-encapsulation layers on perovskite solar cells at 130 °C without damaging the temperature-sensitive perovskite and organic materials. The stability of thep-i-nformamidinium methylammonium lead iodide solar cells under standard ISOS-D-3 testing conditions (65 °C and 85% relative humidity) is significantly enhanced by the encapsulation layers. Specifically, the O3-AlOxand H2O2-AlOxlayers result in a six-fold increase in the time required for the cells to degrade to 80% of their original efficiency compared to un-encapsulated cells.

Thin Film Encapsulation for RF MEMS in 5G and Modern Telecommunication Systems.

In this work, SiNx/a-Si/SiNx caps on conductive coplanar waveguides (CPWs) are proposed for thin film encapsulation of radio-frequency microelectromechanical systems (RF MEMS), in view of the application of these devices in fifth generation (5G) and modern telecommunication systems. Simplification and cost reduction of the fabrication process were obtained, using two etching processes in the same barrel chamber to create a matrix of holes through the capping layer and to remove the sacrificial layer under the cap. Encapsulating layers with etch holes of different size and density were fabricated to evaluate the removal of the sacrificial layer as a function of the percentage of the cap perforated area. Barrel etching process parameters also varied. Finally, a full three-dimensional finite element method-based simulation model was developed to predict the impact of fabricated thin film encapsulating caps on RF performance of CPWs.

Functional Metal Oxides in Perovskite Solar Cells.

As extremely important inorganic materials, metal oxides play an irreplaceable role in solid perovskite solar cells. In this review, the preparation methods of metal oxides, their effects on the perovskite optoelectronic devices incorporated with the energy level compatibility of perovskite materials are provided. Finally, the possible reactions between interfaces during growth progress as well as passivation mechanism of some metal oxides to perovskite materials are discussed. The physical, chemical, and electrical properties of functional metal oxides endow the enhancement of the efficiency and stability of perovskite photovoltaic devices.

Ultrathin, transferred layers of thermally grown silicon dioxide as biofluid barriers for biointegrated flexible electronic systems.

Materials that can serve as long-lived barriers to biofluids are essential to the development of any type of chronic electronic implant. Devices such as cardiac pacemakers and cochlear implants use bulk metal or ceramic packages as hermetic enclosures for the electronics. Emerging classes of flexible, biointegrated electronic systems demand similar levels of isolation from biofluids but with thin, compliant films that can simultaneously serve as biointerfaces for sensing and/or actuation while in contact with the soft, curved, and moving surfaces of target organs. This paper introduces a solution to this materials challenge that combines (i) ultrathin, pristine layers of silicon dioxide (SiO2) thermally grown on device-grade silicon wafers, and (ii) processing schemes that allow integration of these materials onto flexible electronic platforms. Accelerated lifetime tests suggest robust barrier characteristics on timescales that approach 70 y, in layers that are sufficiently thin (less than 1 µm) to avoid significant compromises in mechanical flexibility or in electrical interface fidelity. Detailed studies of temperature- and thickness-dependent electrical and physical properties reveal the key characteristics. Molecular simulations highlight essential aspects of the chemistry that governs interactions between the SiO2 and surrounding water. Examples of use with passive and active components in high-performance flexible electronic devices suggest broad utility in advanced chronic implants.

Recent Achievements for Flexible Encapsulation Films Based on Atomic/Molecular Layer Deposition.

The purpose of this paper is to review the research progress in the realization of the organic-inorganic hybrid thin-film packaging of flexible organic electroluminescent devices using the PEALD (plasma-enhanced atomic layer deposition) and MLD (molecular layer deposition) techniques. Firstly, the importance and application prospect of organic electroluminescent devices in the field of flexible electronics are introduced. Subsequently, the principles, characteristics and applications of PEALD and MLD technologies in device packaging are described in detail. Then, the methods and process optimization strategies for the preparation of organic-inorganic hybrid thin-film encapsulation layers using PEALD and MLD technologies are reviewed. Further, the research results on the encapsulation effect, stability and reliability of organic-inorganic hybrid thin-film encapsulation layers in flexible organic electroluminescent devices are discussed. Finally, the current research progress is summarized, and the future research directions and development trends are prospected.

Optical Monitoring of Water Side Permeation in Thin Film Encapsulation.

The stability of long-term microfabricated implants is hindered by the presence of multiple water diffusion paths within artificially patterned thin-film encapsulations. Side permeation, defined as infiltration of molecules through the lateral surface of the thin structure, becomes increasingly critical with the trend of developing high-density and miniaturized neural electrodes. However, current permeability measurement methods do not account for side permeation accurately nor quantitatively. Here, a novel optical, magnesium (Mg)-based method is proposed to quantify the side water transmission rate (SWTR) through thin film encapsulation and validate the approach using micrometric polyimide (PI) and polyimide-silicon carbide (PI-SiC) multilayers. Through computed digital grayscale images collected with corroding Mg film microcells coated with the thin encapsulation, side and surface WTRs are quantified. A 4.5-fold ratio between side and surface permeation is observed, highlighting the crucial role of the PI-PI interface in lateral diffusion. Universal guidelines for the design of flexible, hermetic neural interfaces are proposed. Increasing encapsulation's width (interelectrode spacing), creating stronger interfacial interactions, and integrating high-barrier interlayers such as SiC significantly enhance the lateral hermeticity.

Zinc Aluminum Oxide Encapsulation Layers for Perovskite Solar Cells Deposited Using Spatial Atomic Layer Deposition.

An atmospheric-pressure spatial atomic layer deposition system is used to rapidly deposit 60 nm zinc-aluminum oxide (Zn-AlOx ) thin-film-encapsulation layers directly on perovskite solar cells at 130 °C without damaging the temperature-sensitive perovskite and organic materials. Varying the Zn/Al ratio has a significant impact on the structural properties of the films and their moisture barrier performance. The Zn-AlOx films have higher refractive indexes, lower concentrations of OH─ groups, and lower water-vapor transmission rates (WVTR) than AlOx films without zinc. However, as the Zn/Al ratio increases beyond 0.21, excess Zn atoms segregate, leading to an increase in the number of available hydroxyl groups on the surface of the deposited film and a slight increase in the WVTR. The stability of the p-i-n formamidinium methylammonium lead iodide solar cells under standard ISOS-D-3 testing conditions (65 °C and 85% relative humidity) is significantly enhanced by the thin encapsulation layers. The layers with a Zn/Al ratio of 0.21 result in a seven-fold increase the time required for the cells to degrade to 80% of their original efficiency.

A Study of Al2O3/MgO Composite Films Deposited by FCVA for Thin-Film Encapsulation.

Al2O3 and MgO composite (Al2O3/MgO) films were rapidly deposited at low temperatures using filtered cathode vacuum arc (FCVA) technology, aiming to achieve good barrier properties for flexible organic light emitting diodes (OLED) thin-film encapsulation (TFE). As the thickness of the MgO layer decreases, the degree of crystallinity decreases gradually. The 3:2 Al2O3:MgO layer alternation type has the best water vapor shielding performance, and the water vapor transmittance (WVTR) is 3.26 × 10-4 g·m-2·day-1 at 85 °C and 85% R.H, which is about 1/3 of that of a single layer of Al2O3 film. Under the action of ion deposition, too many layers will cause internal defects in the film, resulting in decreased shielding ability. The surface roughness of the composite film is very low, which is about 0.3-0.5 nm depending on its structure. In addition, the visible light transmittance of the composite film is lower than that of a single film and increases with the increase in the number of layers.

In Situ Solution-Processed Submicron Thick SiOx Cy /a-SiNx (O):H Composite Barrier Film for Polymer:Non-Fullerene Photovoltaics.

Aiming to improve the environmental stability of organic photovoltaics, a multilayered SiOx Cy /a-SiNx (O):H composite barrier film coated with a hydrophobic perfluoro copolymer stop layer for polymer:non-fullerene solar cells is developed. The composite film is prepared by spin-coating of polysilicone and perhydropolysilazane (PHPS) following a densification process by vacuum ultraviolet irradiation in an inert atmosphere. The transformation of polysilicone and PHPS to SiOx Cy and a-SiNx (O):H is confirmed by Fourier transform infrared and energy-dispersive X-ray spectroscopy measurement. However, the as-prepared PHPS-derived silicon nitride (PDSN) can react with moisture in the ambient atmosphere, yielding microscale defects and a consequent poor barrier performance. Treating the incomplete PDSN with methanol vapor significantly densifies the film yielding low water vapor transmission rates (WVTRs)of 5.0 × 10-1 and 2.0 × 10-1 g m-2  d-1 for the one- and three-couple of SiOx Cy /a-SiNx (O):H (CON) composite films, respectively. By incorporating a thin hydrophobic perfluoro copolymer layer, the three-coupled methanol-treated CON film with a total thickness of 600 nm shows an extremely low WVTR of 8.7 × 10-4 g m-2  d-1 . No performance decay is measured for the PM6:Y6 and PM6:L8-BO cells after such an encapsulation process. These encapsulated polymer cells show good stability storaged at 25 °C/50% relative humidity, or under simulated extreme rainstorm tests.

The Effect of Reactive Sputtering on the Microstructure of Parylene-C.

Sputtering technique involves the use of plasma that locally heats surfaces of substrates during the deposition of atoms or molecules. This modifies the microstructure by increasing crystallinity and the adhesive properties of the substrate. In this study, the effect of sputtering on the microstructure of parylene-C was investigated in an aluminum nitride (AlN)-rich plasma environment. The sputtering process was carried out for 30, 45, 90 and 120 min on a 5 µm thick parylene-C film. Topography and morphology analyses were conducted on the parylene-C/AlN bilayers. Based on the experimental data, the results showed that the crystallinity of parylene-C/AlN bilayers was increased after 30 min of sputtering and remained saturated for 120 min. A scratch-resistance test conducted on the bilayers depicted that a higher force is required to delaminate the bilayers on top of the substrate. Thus, the adhesion properties of parylene-C/AlN bilayers were improved on glass substrate by about 17% during the variation of sputtering time.

A Review of Various Attempts on Multi-Functional Encapsulation Technologies for the Reliability of OLEDs.

As the demand for flexible organic light-emitting diodes (OLEDs) grows beyond that for rigid OLEDs, various elements of OLEDs, such as thin-film transistors, electrodes, thin-film encapsulations (TFEs), and touch screen panels, have been developed to overcome OLEDs' physical and chemical limitations through material and structural design. In particular, TFEs, which protect OLEDs from the external environment, including reactive gases, heat, sunlight, dust, and particles, have technical difficulties to be solved. This review covers various encapsulation technologies that have been developed with the advent of atomic layer deposition (ALD) technology for highly reliable OLEDs, in which solutions to existing technical difficulties in flexible encapsulations are proposed. However, as the conventional encapsulation technologies did not show technological differentiation because researchers have focused only on improving their barrier performance by increasing their thickness and the number of pairs, OLEDs are inevitably vulnerable to environmental degradation induced by ultraviolet (UV) light, heat, and barrier film corrosion. Therefore, research on multi-functional encapsulation technology customized for display applications has been conducted. Many research groups have created functional TFEs by applying nanolaminates, optical Bragg mirrors, and interfacial engineering between layers. As transparent, wearable, and stretchable OLEDs will be actively commercialized beyond flexible OLEDs in the future, customized encapsulation considering the characteristics of the display will be a key technology that guarantees the reliability of the display and accelerates the realization of advanced displays.

Design of a Flexible Thin-Film Encapsulant with Sandwich Structures of Perhydropolysilazane Layers.

Perovskite solar cells (PSCs) have attracted considerable attention due to their excellent photovoltaic properties, but stability issues have prevented their widespread application. PSCs must be protected by encapsulation to extend their lifetime. Here, we show that perhydropolysilazane (PHPS)-based multilayered encapsulation improves the lifetime of PSCs. The PSCs were encapsulated by converting PHPS into silica under vacuum ultraviolet (UV) irradiation. The PHPS-based multilayer encapsulation method achieved a sandwich structure of PHPS/poly(ethylene terephthalate) (PET)/PHPS with a water vapor transmission rate (WVTR) of 0.92 × 10-3 gm-2 d-1 (at 37.8 °C and 100% relative humidity). We then performed a reservoir test of the encapsulated PSCs to confirm the moisture stability of the encapsulation based on PHPS/PET/PHPS barrier films. The cell lifetime remained stable even after 1000 h of ambient-temperature operation. Finally, we analyzed the mechanical flexibility of the PHPS/PET/PHPS multibarrier through bending tests. The multibarrier exhibited high mechanical stability with no large increase in WVTR after bending.

Thin Film Encapsulation for LCP-Based Flexible Bioelectronic Implants: Comparison of Different Coating Materials Using Test Methodologies for Life-Time Estimation.

Liquid crystal polymer (LCP) has gained wide interest in the electronics industry largely due to its flexibility, stable insulation and dielectric properties and chip integration capabilities. Recently, LCP has also been investigated as a biocompatible substrate for the fabrication of multielectrode arrays. Realizing a fully implantable LCP-based bioelectronic device, however, still necessitates a low form factor packaging solution to protect the electronics in the body. In this work, we investigate two promising encapsulation coatings based on thin-film technology as the main packaging for LCP-based electronics. Specifically, a HfO2-based nanolaminate ceramic (TFE1) deposited via atomic layer deposition (ALD), and a hybrid Parylene C-ALD multilayer stack (TFE2), both with a silicone finish, were investigated and compared to a reference LCP coating. T-peel, water-vapour transmission rate (WVTR) and long-term electrochemical impedance spectrometry (EIS) tests were performed to evaluate adhesion, barrier properties and overall encapsulation performance of the coatings. Both TFE materials showed stable impedance characteristics while submerged in 60 °C saline, with TFE1-silicone lasting more than 16 months under a continuous 14V DC bias (experiment is ongoing). The results presented in this work show that WVTR is not the main factor in determining lifetime, but the adhesion of the coating to the substrate materials plays a key role in maintaining a stable interface and thus longer lifetimes.

Stability of SiNx Prepared by Plasma-Enhanced Chemical Vapor Deposition at Low Temperature.

In this paper, the environmental stability of silicon nitride (SiNx) films deposited at 80 °C by plasma-enhanced chemical vapor deposition was studied systematically. X-ray photoelectron spectroscopy and Fourier transform infrared reflection were used to analyze the element content and atomic bond structure of the amorphous SiNx films. Variation of mechanical and optical properties were also evaluated. It is found that SiNx deposited at low temperature is easily oxidized, especially at elevated temperature and moisture. The hardness and elastic modulus did not change significantly with the increase of oxidation. The changes of the surface morphology, transmittance, and fracture extensibility are negligible. Finally, it is determined that SiNx films deposited at low-temperature with proper processing parameters are suitable for thin-film encapsulation of flexible devices.

Nano-Laminated Metal Oxides/Polyamide Stretchable Moisture- and Gas-Barrier Films by Integrated Atomic/Molecular Layer Deposition.

Stretchable barrier films capable of maintaining high levels of moisture- and gas-barrier performance under significant mechanical strains are a critical component for wearable/flexible electronics and other devices, but realization of stretchable moisture-barrier films has not been possible due to the inevitable issues of strain-induced rupturing compounded with moisture-induced swelling of a stretched barrier film. This study demonstrates nanolaminated polymer/metal oxide stretchable moisture-barrier films fabricated by a novel molecular layer deposition (MLD) process of polyamide-2,3 (PA-2,3) integrated with atomic layer deposition (ALD) metal oxide processes and an in situ surface-functionalization technique. The PA-2,3 surface upon in situ functionalization with H2O2 vapor offers adequate surface chemisorption sites for rapid nucleation of ALD oxides, minimizing defects at the PA-2,3/oxide interfaces in the nanolaminates. The integrated ALD/MLD process enables facile deposition and precise structural control of many-layered oxide/PA-2,3 nanolaminates, where the large number of PA-2,3 nanolayers provide high tolerance against mechanical stretching and flexing thanks to their defect-decoupling and stress-buffering functions, while the large number of oxide nanolayers shield against swelling by moisture. Specifically, a nanolaminate with 72 pairs of alternating 2 nm (5 cycles) PA-2,3 and 0.5 nm HfO2 (five cycles) maintains its water vapor transmission rate (WVTR) at the 10-6 g/m2 day level upon 10% tensile stretching and 2 mm-radius bending, a significant breakthrough for the wearable/flexible electronics technologies.

Bioinspired Oil-Infused Slippery Surfaces with Water and Ion Barrier Properties.

Encapsulation materials play an important role in many applications including wearable electronics, medical devices, underwater robotics, marine skin tagging system, food packaging, and energy conversation and storage devices. To date, all the encapsulation materials, including polymer layers and inorganic materials, are solid materials. These solid materials suffer from limited barrier lifetimes due to pinholes, cracks, and nanopores or from complicated fabrication processes and limited stretchability for interfacing with complex 3D surfaces. This paper reports a solution to this material challenge by demonstrating bioinspired oil-infused slippery surfaces with excellent waterproof property for the first time. A water vapor transmission test shows that locking a thin layer of oil on the silicone elastomer improves the water vapor barrier performance by three orders of magnitude. Accelerated lifetime tests suggest robust water barrier characteristics that approach 226 days at 37 °C even under severe mechanical damage. A combination of temperature- and thickness-dependent experimental measurements and reaction-diffusion modeling reveals the key waterproof property. In addition to serving as a barrier to water, the oil-infused surface demonstrates an attractive ion barrier property. All these exceptional properties suggest the potential applications of slippery surfaces as encapsulation materials for medical devices, underwater electronics, and many others.

Organic/Inorganic Hybrid Thin-Film Encapsulation Using Inkjet Printing and PEALD for Industrial Large-Area Process Suitability and Flexible OLED Application.

We present herein the first report of organic/inorganic hybrid thin-film encapsulation (TFE) developed as an encapsulation process for mass production in the display industry. The proposed method was applied to fabricate a top-emitting organic light-emitting device (TEOLED). The organic/inorganic hybrid TFE has a 1.5 dyad structure and was fabricated using plasma-enhanced atomic layer deposition (PEALD) and inkjet printing (IJP) processes that can be applied to mass production operations in the industry. Currently, industries use inorganic thin films such as SiNx and SiOxNy fabricated through plasma-enhanced chemical vapor deposition (PECVD), which results in film thickness >1 µm; however, in the present work, an Al2O3 inorganic thin film with a thickness of 30 nm was successfully fabricated using ALD. Furthermore, to decouple the crack propagation between the adjacent Al2O3 thin films, an acrylate-based polymer layer was printed between these layers using IJP to finally obtain the 1.5 dyad hybrid TFE. The proposed method can be applied to optoelectronic devices with various form factors such as rollables and stretchable displays. The hybrid TFE developed in this study has a transmittance of 95% or more in the entire visible light region and a very low surface roughness of less than 1 nm. In addition, the measurement of water vapor transmission rate (WVTR) using commercial MOCON equipment yielded a value of 5 × 10-5 gm-2 day-1 (37.8 °C and 100% RH) or less, approaching the limit of the measuring equipment. The TFE was applied to TEOLEDs and the improvement in optical properties of the device was demonstrated. The OLED panel was manufactured and operated stably, showing excellent consistency even in the actual display manufacturing process. The panel operated normally even after 363 days in air. The proposed organic/inorganic hybrid encapsulant manufacturing process is applicable to the display industry and this study provides basic guidelines that can serve as a foothold for the development of various technologies in academia and industry alike.