Device Degradation Mechanisms Research Articles

Cross-Sectional Preparation of Complex Energy Devices and Their Characterization By Advanced Microscopic Methods

Energy devices such as batteries, fuel cells, and solar cells are composed of multiple functional components with varying material properties. Achieving a fundamental understanding of structure-property relationships and systematically enhancing performance, while also investigating device degradation and failure mechanisms, requires high-quality cross-sections of entire devices or substantial regions. Given that many devices contain different classes of materials, including liquid and/or air-sensitive components, working under cryogenic or inert conditions is necessary to maintain their original state. To facilitate cross-sectional characterization of these devices from the macroscopic down to the atomic level, we use a range of preparation tools. A self-designed cryo-cutter allows us to efficiently produce cross-sections of entire devices, such as pouch cells, in a single step, enabling optical microscopy (OM) observation at the centimeter scale while preserving their pristine state. For finer scales, cryo-ultramicrotomy and focused ion beam (FIB) techniques are regularly employed. These methods can prepare high-quality thin samples under 50 nm for investigations using OM, scanning electron microscopy (SEM), and transmission electron microscopy (TEM) at atomic resolution. In this presentation, we demonstrate the scale-bridging capabilities of these preparation techniques applied to various devices and their components in conjunction with advanced electron microscopic and spectroscopic methods. Examples include devices such as batteries (Fig. 1) and complex proton exchange membrane (PEM) fuel cells, as well as battery components (Fig. 2). The techniques used are ideal for assessing the integrity of entire devices and the interfaces of individual layers and components, including their morphology, contact, composition, and chemical bonding states. Acknowledgement: Part of this work was performed at the Micro-and Nanoanalytics Facility (MNaF) of the University of Siegen. Figure 1

Charge transport dynamics and emission response in quantum-dot light-emitting diodes for next-generation high-speed displays

Inorganic quantum-dot light-emitting diodes (QD-LEDs) have gained significant attention as optoelectronic devices for next-generation display systems due to their superior colour properties. A comprehensive understanding of the charge transport dynamics and transient emission responses of the QD-LED is crucial to achieving high motion picture quality next-generation QD-LED display systems. In this study, we investigated the transient emission response of QD-LED devices through an advanced charge transport simulation model tailored to the quantum-dots (QDs). The dynamic response of the QD-LED devices is evaluated using the time-resolved electroluminescence measurement method for both cadmium-based and cadmium-free red, green, and blue QD-LEDs. The QD-LED devices exhibit notable emission drops during pulse voltage application. The charge transport simulation quantitatively reveals that the on and off switching speeds and the emission drops are intricately influenced by the electron and hole injection balance and a combination of carrier recombination factors within the QD layer. The charge transport simulation also shows that space-charge accumulation, due to the combined effects of charge imbalance and Auger recombination, quantitatively explains a potential device degradation mechanism. Therefore, the QD-specified charge transport model provides a crucial approach in designing and optimizing QD-LED devices for next-generation high-speed QD-LED displays with ultimate colour quality and long lifetimes.

A Brief Review of Single-Event Burnout Failure Mechanisms and Design Tolerances of Silicon Carbide Power MOSFETs

Radiation hardening of power MOSFETs (metal oxide semiconductor field effect transistors) is of the highest priority for sustaining high-power systems in the space radiation environment. Silicon carbide (SiC)-based power electronics are being investigated as a strong alternative for high power spaceborne power electronic systems. SiC MOSFETs have been shown to be most prone to single-event burnout (SEB) from space radiation. The current knowledge of SiC MOSFET device degradation and failure mechanisms are reviewed in this paper. Additionally, the viability of radiation tolerant SiC MOSFET designs and the modeling methods of SEB phenomena are evaluated. A merit system is proposed to consider the performance of radiation tolerance and nominal electrical performance. Criteria needed for high-fidelity SEB simulations are also reviewed. This paper stands as a necessary analytical review to intercede the development of radiation-hardened power devices for space and extreme environment applications.

Bilayer channel structure to improve the stability of solution-processed metal oxide transistors under AC stress

In this work, we report solution-processed bilayer channel thin film transistors (TFTs) based on solution-processed amorphous oxide semiconductors (AOSs) that fulfill both superb electrical performance and device stability against applied alternating current (AC) drain bias stress. Acceptor-like states generation via hot carrier effect (HCE) is a representative device degradation mechanism suggested for AOS-based TFTs when subjected to AC bias stress, featuring threshold voltage (Vth) shift and on-current (Ion) lowering. As excess electric field and accumulated carriers in the AOS channel cause HCE, alleviating carrier accumulation is a key solution for mitigating HCE. Bilayer channel TFTs comprising two different AOSs could work as a countermeasure to overcome HCE since proper energy band alignment of two channels creates a conduction band difference that act as the energy barrier for carriers. In this regard, we employed amorphous indium-gallium-zinc oxide (IGZO) and zinc-tin oxide (ZTO) as bottom and top layer, respectively, for bilayer channel TFT. Designed bilayer channel showed a conduction band difference of 0.18 eV, and fabricated TFT based on this architecture exhibited high mobility over to 5.9 cm2/Vs with slight Vth shift of 0.1 V and Ion lowering of 1.7% for 1000 s against applied AC stress, demonstrating device stability under AC drain bias stress.

Characteristics and Degradation Mechanisms under High Reverse Base-Collector Bias Stress in InGaAs/InP Double HBTs.

In this paper, the reliability of InP/InGaAs DHBTs under high reverse base-collector bias stress is analyzed by experiments and simulation. The DC characteristics and S parameters of the devices under different stress times were measured, and the key parameters with high field stress were also extracted to fully understand and analyze the high-field degradation mechanism of devices. The measurements indicate that the high-field stress leads to an increase in base current, an increase in base-collector (B-C) and base-emitter (B-E) junction leakage current, and a decrease in current gain, and different degrees of degradation of key parameters over stress time. The analysis reveals that the degradation caused by reverse high-field stress mainly occurs in the B-C junction, access resistance degradation, and passivation layer. The physical origins of these failure mechanisms have been studied based on TCAD simulation, and a physical model is proposed to explain the experimental results.

Investigation of the Degradation Mechanism of SiC MOSFET Subjected to Multiple Stresses.

The performance requirements for power devices in airborne equipment are increasingly demanding, while environmental and working stresses are becoming more diverse. The degradation mechanisms of devices subjected to multiple stresses become more complex. Most proposed degradation mechanisms and models in current research only consider a single stress, making it difficult to describe the correlation between multiple stresses and the correlation of failures. Then, a multi-physical field coupling model based on COMSOL is proposed. The influence relationship between temperature, moisture, electrical load, and vibration during device operation is considered, and a three-dimensional finite element model is built to investigate the multi-stress degradation mechanism under multi-physical field coupling. The simulation results show that, compared with single-stress models, the proposed multi-stress coupled model can more accurately simulate the degradation process of SiC MOSFET. This provides references for improving the reliability design of power device packaging.

Luminescence and Degeneration Mechanism of Perovskite Light-Emitting Diodes and Strategies for Improving Device Performance.

Perovskite light-emitting diodes (PeLEDs) can be a promising technology for next-generation display and lighting applications due to their excellent optoelectronic properties. However, a systematical overview of luminescence and degradation mechanism of perovskite materials and PeLEDs is lacking. Therefore, it is crucial to fully understand these mechanisms and further improve device performances. In this work, the fundamental photophysical processes of perovskite materials, electroluminescence mechanism of PeLEDs including carrier kinetics and efficiency roll-off as well as device degradation mechanism are discussed in detail. In addition, the strategies to improve device performances are summarized, including optimization of photoluminescence quantum yield, charge injection and recombination, and light outcoupling efficiency. It is hoped that this work can provide guidance for future development of PeLEDs and ultimately realize industrial applications.

Beyond Protocols: Understanding the Electrical Behavior of Perovskite Solar Cells by Impedance Spectroscopy

AbstractImpedance spectroscopy (IS) is an effective characterization technique used to probe and distinguish charge dynamics occurring at different timescales in optoelectronic and electric devices. With the rapid rise of research being conducted on perovskite solar cells (PSCs), IS has significantly contributed to the understanding of their device performance and degradation mechanisms, including metastable effects such as current–voltage hysteresis. The ionic–electronic behavior of PSCs and the presence of a wide variety of perovskite compositions and cell architectures add complexity to the accurate interpretation of the physical processes occurring in these devices. In this review, the most common IS protocols are explained to help perform accurate impedance measurements on PSC devices. It critically reviews the most commonly used equivalent circuits alongside drift‐diffusion modeling as a complementary technique to analyze the impedance response of PSCs. As an emerging method for characterizing the interfacial recombination between the perovskite layer and selective contacts, light intensity modulated impedance spectroscopy technique is further discussed. Lastly, important works on the application of IS measurement protocols for PSCs are summarized followed by a detailed discussion, providing a critical perspective and outlook on the growing topic of IS on PSCs.

Synergetic Acceleration on the Degradation of Flexible Perovskite Solar Cells under Light and Stress Cooperation

Metal‐halide perovskites represent highly efficient and lightweight photovoltaic technology with promising applications in various scenarios. However, their stability is often deteriorated by various external factors in realistic applications, which is particularly severe for flexible devices. Herein this work, the degradation of flexible perovskite devices is focused on under two substantial factors: light and mechanical stress, where the degradation is surprisingly accelerated with simultaneous existence of these factors. Full‐scale analysis demonstrates that the mismatch and charge accumulation at the interfaces are direct causes of this device failure. Theoretical simulations reveal that carrier‐localization behavior, which is strongly associated with lattice distortion, is the core microscopic factor that destabilizes the device. This finding poses significant challenges to the stability of flexible perovskite devices and other inner strain‐sensitive systems, which cannot be simply mitigated by conventional passivation or encapsulation. It is suggested in theoretical studies that this effect may be suppressed by certain physical modulations, such as external electric fields. In general, a better understanding of the degradation mechanisms of realistic flexible and rigid perovskite devices can be contributed in this study and the development of solutions is facilitated to address those challenges.

Device Structures of Perovskite Solar Cells: A Critical Review

In recent years, perovskite solar cells (PSCs) have been in huge demand because of their ease of production, low cost, flexibility, long diffusion length, lightweight, and higher performance than their counterparts. The PSCs have demonstrated remarkable progress with power conversion efficiency (PCE) up to 25.7% using FAPbI3 as an active layer component. However, lower PCE and device stability restrict PSCs' commercial viability. Further, the photocurrents in PSCs are close to the maximum Shockley–Queisser (SQ) limit. The focus now is on enhancing the open‐circuit voltage and fill factor through modifying charge‐selective contacts, the morphology of perovskite material, and interface modification. The large grain size, uniformity, and coverage area distinguish the crucial factors affecting the PCE of PSCs. Long‐term device stability and degradation mechanisms have also shown significant dependence on the device structure. Therefore, the tailoring of the device structure continues to play a crucial role in the device's performance and stability. In this review, the illustration of the structural development of perovskite solar cells, including advanced interfacial layers and their associated parameters, is discussed in detail. In addition, the challenges that hinder the PSCs' performance are also discussed.

Optimizing microdisplay requirements for pancake VR applications

AbstractVirtual reality (VR) devices use imaging optics to magnify the microdisplay images for providing an immersive viewing experience. A microdisplay is preferred to have high‐resolution density and high dynamic range to meet the demanding requirements of human vision system (HVS), for example, visual acuity >60 pixels per degree and grayscale depth >10 bits. However, increasing resolution density and dynamic range often lead to a reduced optical efficiency and sophisticated fabrication process of the microdisplay panels. In this paper, we systematically analyze the image degradation mechanisms of VR devices caused by both imaging optics and microdisplay and find that the image degradation caused by imaging optics significantly unleash the requirements of microdisplay, such as contrast ratio, number of local dimming zones, and resolution density. For example, aberrations of the imaging optics reduce the resolution density requirement of the microdisplay, and stray light of the imaging optics relieves the contrast ratio requirement of the microdisplay. These results help prevent excessive design of microdisplay, for example, mini‐light‐emitting diode (LED) backlit liquid‐crystal displays (LCDs), organic LEDs, or micro‐LEDs, in a pancake lens‐based VR headset.

Degradation Mechanisms and Lifetime Modeling of Power Semiconductor Devices

Lifetime modeling and predicting for power semiconductor devices has become important due to higher demands on reliability and economy, i.e. to save time and money. Understanding the degradation mechanisms of such devices in a complex interplay of thermal, mechanical, and electrical loading in often harsh environment is a very challenging task, involving the competences of electronic engineers, simulation experts, materials scientists, physicists and mathematicians – with the final goal to permit accurate prediction of failure probabilities in the ppm-range as a function of time. In this review paper, I’ve discussed previously published literature on degradation mechanisms, experimental results obtained in several studies, lifetime prediction procedure, lifetime model and some preventive measures that can be taken against permanent damage.

Advances and perspective on the translational medicine of biodegradable metals.

ABSTRACTBiodegradable metals, designed to be safely degraded and absorbed by the body after fulfil the intended functions, are of particular interest in the 21st century. The marriage of advanced biodegradable metals with clinical needs have yield unprecedented possibility. Magnesium, iron, and zinc-based materials constitute the main components of temporary, implantable metallic medical devices. A burgeoning number of studies on biodegradable metals have driven the clinical translation of biodegradable metallic devices in the fields of cardiology and orthopaedics over the last decade. Their ability to degrade as well as their beneficial biological functions elicited during degradation endow this type of material with the potential to shift the paradigm in the treatment of musculoskeletal and cardiovascular diseases. This review provides an insight into the degradation mechanism of these metallic devices in specific application sites and introduces state-of-the-art translational research in the field of biodegradable metals, as well as highlighting some challenges for materials design strategies in the context of mechanical and biological compatibility.

Degradation analysis of doped organic p-n heterojunction charge generation layers by impedance and optical spectroscopy

Investigation of the long-term stability of charge generation layers (CGLs) provides a fundamental and an essential approach in achieving highly efficient tandem organic electronic devices. Thus, in this foremost study, the degradation mechanism of electrically aged organic p-n heterojunction CGLs has been investigated by impedance and optical spectroscopy. Rubidium carbonate (Rb2CO3)–doped 2,2,2-(1,3,5-benzinetriyl)-tris(1-phenyl-1H-benzimidazole) (TPBi) and molybdenum trioxide (MoO3)–doped 1,4-bis[N-(1-naphthyl)-N′-phenylamino]-4,4′-diamine (NPB) are used as the n-type and p-type organic semiconductors, respectively. A detailed analysis from capacitance-frequency (C–F) and capacitance-voltage (C–V) characteristics reveals reduced charge generation and 19.6% reduction in the geometric capacitance of the CGL after electrical aging. Reduced peak intensity from UV–Vis–NIR spectra of the aged CGL points to 21.4% charge transfer complex decomposition of the Rb2CO3-doped TPBi. We propose that the rate-limiting step of charge generation in the CGL is caused by the electron transport in the TPBi:Rb2CO3 layer and not the charge generation itself at the TPBi:Rb2CO3/NPB:MoO3 heterojunction. This simple, comprehensive, and non-destructive technique facilitates a crucial analysis that underpins the mechanism of device degradation and further provides a fundamental approach in developing highly stable CGLs for efficient organic electronic devices.

Comparative study of As and Cu doping stability in CdSeTe absorbers

The reasons behind the long-term degradation of Cu-doped CdTe thin-film solar cells have been a topic of discussion for almost two decades. Yet the underlying mechanisms of such degradation, especially interactions of Cu doping with Cl in high-performance CdSeTe devices, still lack detailed understanding. In this study, we provide a consistent theoretical analysis of the fundamental physics behind this phenomenon. We then identify the dominant device degradation mechanism that cannot be completely eliminated in Cu-doped chlorinated CdSeTe-based PV. Finally, we conclude that this key mechanism is absent in CdSeTe PV when using arsenic absorber doping, which explains the remarkable stability demonstrated by this new technology. Theoretical conclusions are supported by the results of accelerated life tests on Cu- and As-doped chlorinated CdSeTe cells.

Hot-Carrier-Induced Reliability for Lateral DMOS Transistors With Split-STI Structures

In this work, four kinds of lateral double-diffused MOS (LDMOS) devices with different split shallow trench isolation (STI) structures (Device A: LDMOS with traditional split-STI, Device B: LDMOS with slope-STI, Device C with step-STI and Device D with H-shape-STI) have been fabricated and the hot-carrier reliabilities also have been investigated due to the serious environment they are endured. The maximum bulk current (Ibmax) stress and the maximum gate voltage (Vgmax) stress have been carried out and the inner mechanism of device degradation have been investigated successfully. With the assistance of the T-CAD simulation tools, it is found that the main damage point locates at the STI conners with a mount of interface states generation, inducing serious degradation for these four devices. The Device D owns high hot-carrier reliability due to its special structure with narrow split-STI. The worst device is Device C because of the presence of extra STI damage point. Finally, a mechanism verification, the charge pumping (CP) method has been applied to better understand this work.

Improving the Thermal Stability of Top‐Emitting Organic Light‐Emitting Diodes by Modification of the Anode Interface

AbstractTop‐emitting organic light‐emitting diodes (OLEDs) are of interest for numerous applications, in particular for displays with high fill factors. To maximize efficiency and luminance, molecular p‐doping of the hole transport layer (p‐HTL) and a highly reflective anode contact, for example, made from silver, are used. Atomic layer deposition (ALD) is attractive for thin film encapsulation of OLEDs but generally requires a minimum process temperature of 80 °C. Here it is reported that the interface between the p‐HTL and the silver anode of top‐emitting OLEDs degrades during an 80 °C ALD encapsulation process, causing an over fourfold reduction in OLED current and luminance. To understand the underlying mechanism of device degradation, single charge carrier devices are investigated before and after annealing. A spectroscopic study of p‐HTLs indicates that degradation is due to the interaction between diffusing silver ions and the p‐type molecular dopant. To improve the stability of the interface, either an ultrathin MoO3 buffer layer or a bilayer HTL is inserted at the anode/organic interface. Both approaches effectively suppress degradation. This work shows a route to successful encapsulation of top‐emitting OLEDs using ALD without sacrificing device performance.

Performance degradation mechanism of the light-activated room temperature NO2 gas sensor based on Ag-ZnO nanoparticles

The chemiresistor-type sensors based on Ag-ZnO nanostructures have shown excellent sensing properties to NO2 under visible light irradiation, however, they cannot escape from the destiny of the performances degraded by long-term operation. So, aiming at improving the long-term stability, the revelation of the essence of performance degradation is crucial and also a great challenge. Here, we comparatively investigated the change rules of NO2 sensing properties after running the as-fabricated Ag-ZnO nanoparticles-based sensor multiple times during 60 days under UV and visible light irradiation. It is demonstrated that the room temperature light-activated (especially UV light) NO2 sensing performances (response and sensitivity) of the sensor degrade after running multiple times. The degraded performances can be attributed to the deteriorated crystal quality and increased oxygen vacancy defects of the sensing materials, and oxidization of more Ag0 into Ag+ on the ZnO surfaces, which greatly increase the free charge carrier concentration in the dark and decrease photogenerated charge carrier concentration under light irradiation. Correspondingly, the photoconductivity of the device declines and its output resistance signal weakens. This work offers not only a fundamental understanding of the performance degradation of the light-activated room temperature NO2 gas sensor, but also a strategy for the study on the performance degradation mechanism of other devices.

Suppressing Ion Migration across Perovskite Grain Boundaries by Polymer Additives

AbstractPassivation of organometal halide perovskites with polar molecules has been recently demonstrated to improve the photovoltaic device efficiency and stability. However, the mechanism is still elusive. Here, it is found that both polymers with large and small dipole moment of 3.7 D and 0.6 D have negligible defect passivation effect on the MAPbI3 perovskite films as evidenced by photothermal deflection spectroscopy. The photovoltaic devices with and without the polymer additives also have comparable power conversion efficiencies around 19%. However, devices with the additives have noticeable improvement in stability under continuous light irradiation. It is found that although the initial mobile ion concentrations are comparable in both devices with and without the additives, the additives can strongly suppress the ion migration during the device operation. This contributes to the significantly enhanced electrical‐field stress tolerance of the perovskite solar cells (PVSCs). The PVSCs with polymer additives can operate up to −2 V reverse voltage bias which is much larger than the breakdown voltage of −0.5 V that has been commonly observed. This study provides insight into the role of additives in perovskites and the corresponding device degradation mechanism.

Meeting High Stability and Efficiency in Hybrid Light‐Emitting Diodes Based on SiO2/ZrO2 Coated CsPbBr3 Perovskite Nanocrystals

AbstractSignificant advances are realized in perovskite‐converted hybrid light‐emitting diodes (pc‐HLEDs). However, long‐living devices at high efficiencies still represent a major milestone with average stabilities of <200 h at ≈50 lm W−1 under low applied currents (<15 mA). Herein, a dual metal oxide‐coated CsPbBr3@SiO2/ZrO2 composite is prepared in a one‐pot synthesis through the kinetic control of the sol–gel reaction, followed by a gentle drying process in air. These hybrid nanoparticles show photoluminescence quantum yields of ≈65% that are stable under temperature, ambient, and irradiation stress scenarios. This is translated to pc‐HLEDs with a near‐unity conversion efficiency at any applied current, high efficiencies around 75 lm W−1, and one of the most remarkable stabilities of ≈200 and 700 h at 100 and 10 mA, respectively. In addition, the device degradation mechanism is thoughtfully rationalized comparing devices operating under ambient/inert conditions. As such, this work provides three milestones: i) a new room temperature one‐pot protocol to realize the first SiO2/ZrO2 metal oxide coating that effectively protects the emitting perovskite nanoparticle core, ii) one of the most stable and efficient pc‐HLEDs operating under ambient condition at any applied current, and iii) new insights for the degradation of pc‐HLEDs.