Device Instability Research Articles

Internal Encapsulation Enables Efficient and Stable Perovskite Solar Cells

AbstractPerovskite solar cells (PSCs) have made significant strides in efficiency, but their long‐term stability remains a challenge. While external encapsulation mitigates extrinsic degradation and lead leakage, it does not fully address performance decline due to ion migration within the perovskite devices. Therefore, an internal encapsulation layer that can selectively transport charge carriers and suppress ion migration across the interface is of great significance for achieving long‐term stability in these devices. Here, polytetrafluoroethylene (PTFE) can serve as an effective internal encapsulation layer between the perovskite film and the electron transport layer in the inverted PSCs is demonstrated. The PTFE layer can selectively transport electrons and suppress ion diffusion, resulting in a higher power conversion efficiency (PCE) of 25.49% compared to 24.74% of the control devices and much better long‐term stability. Even after 1500 h of air exposure, the internal encapsulated perovskite devices can maintain 92.6% of their original PCE, outperforming the control devices at 80.4%. This approach offers a novel solution for addressing ion migration‐induced instability in perovskite devices.

Thermoelectric Performance in Triplet‐Ground‐State Polymer Intrinsically Boosted by Enhanced Proquinoidal Characteristic

AbstractOver the past decade, polymer thermoelectric materials featuring flexibility, lightness, and bio‐friendliness have been paid increasing attention as promising candidates for waste heat recovery and energy generation. For a long time, the dominant approach to optimizing the thermoelectric performance of most organic materials is chemical doping, which, however, is not always ideal for practical applications due to its tendency to involve intricate processing procedure and trigger material and device instability. Currently, the pursuit of single‐component neutral thermoelectric materials without exogenous doping presents a compelling alternative. In this work, we designed and synthesized a high‐spin polymer material, PBBT‐TT, by simultaneously employing thieno[3,4‐b]thiophene (TbT) and benzo[1,2‐c : 4,5‐c′]bis[1,2,5]thiadiazole (BBT) units with pronounced proquinoidal characteristics, its analogue, PBBT‐T to demonstrate the effect of the TbT unit was also synthesized. The results indicate that because of the enhanced quinoidal resonance, increased spin density and strong intermolecular antiferromagnetic coupling, PBBT‐TT exhibits high intrinsic electrical conductivity and Seebeck coefficient, which showcases an outstanding power factor of 26.1 μW m−1 K−2 without doping. This achievement surpasses other neutral organic conjugated polymer and radical conductors, and is even comparable to some typical early‐stage doped polymers. Notably, PBBT‐TT exhibits remarkable ambient stability, retaining its initial thermoelectric performance over a 120‐day period. Our finding demonstrates that modulating the intermolecular spin interactions in open‐shell polymers through the introduction of strong proquinoidal units is an effective strategy for the development of doping‐free, intrinsically high‐performance polymer thermoelectric materials.

Thermoelectric Performance in Triplet-Ground-State Polymer Intrinsically Boosted by Enhanced Proquinoidal Characteristic.

Over the past decade, polymer thermoelectric materials featuring flexibility, lightness, and bio-friendliness have been paid increasing attention as promising candidates for waste heat recovery and energy generation. For a long time, the dominant approach to optimizing the thermoelectric performance of most organic materials is chemical doping, which, however, is not always ideal for practical applications due to its tendency to involve intricate processing procedure and trigger material and device instability. Currently, the pursuit of single-component neutral thermoelectric materials without exogenous doping presents a compelling alternative. In this work, we designed and synthesized a high-spin polymer material, PBBT-TT, by simultaneously employing thieno[3,4-b]thiophene (TbT) and benzo[1,2-c : 4,5-c']bis[1,2,5]thiadiazole (BBT) units with pronounced proquinoidal characteristics, its analogue, PBBT-T to demonstrate the effect of the TbT unit was also synthesized. The results indicate that because of the enhanced quinoidal resonance, increased spin density and strong intermolecular antiferromagnetic coupling, PBBT-TT exhibits high intrinsic electrical conductivity and Seebeck coefficient, which showcases an outstanding power factor of 26.1 μW m-1 K-2 without doping. This achievement surpasses other neutral organic conjugated polymer and radical conductors, and is even comparable to some typical early-stage doped polymers. Notably, PBBT-TT exhibits remarkable ambient stability, retaining its initial thermoelectric performance over a 120-day period. Our finding demonstrates that modulating the intermolecular spin interactions in open-shell polymers through the introduction of strong proquinoidal units is an effective strategy for the development of doping-free, intrinsically high-performance polymer thermoelectric materials.

Physical Insights Into the Drain Current Injection-Induced Device Instabilities in AlGaN/GaN HEMTs

Physical Insights Into the Drain Current Injection-Induced Device Instabilities in AlGaN/GaN HEMTs

Quantum coupling and self-heating impacts on threshold voltages of GaN metal–insulator-semiconductor high-electron-mobility transistors

A transient heat conduction equation has been proposed to describe the cooling process of a hot two-dimensional electron gas layer in a GaN-based transistor. This equation serves as the basis for a physical analytical model that explains the impacts of hot electrons in the hot two-dimensional electron gas layer via quantum coupling on the threshold voltage of GaN-based transistors. The temperature of the two-dimensional electron gas layer decreases to ambient temperature as time increases, and the threshold voltage shifts caused by such a temperature will recover with time. The proposed model accurately reflects the observed recovery of threshold voltage over time in experiments. At the same time, it offers insight into how the gate voltage, the source-drain voltage, and the ambient temperature can shift the threshold voltage in these transistors. The simplicity and analytic nature of this proposed model not only provide a physical origin of the threshold voltage instability in GaN-based devices but also offer the possibility for improving device reliability by selecting appropriate device physical parameters.

Improving Hybrid Tin Halide Films of Lead-Free Perovskite Solar Cells with a Volatile Additive of Dipropyl Sulfide.

Lead-free perovskite solar cells with hybrid tin halides (Sn-PVKs) as harvesters have attracted attention with respect to eliminating the contamination of conventional hybrid lead halides. However, Sn-PVK films usually have inferior performance due to rapid crystallization and uncontrollable morphology. Moreover, Sn2+ ions suffer from irreversible oxidation that results in self-doping and device instability. Additive engineering is a key strategy for improving the quality of Sn-PVK films, but solid residues of additives could degrade the transport-recombination process. In this work, dipropyl sulfide (DPS) was introduced as a volatile additive into the precursor solution, and no residue exists in the Sn-PVK films after thermal annealing. The coordinating ability of DPS molecules stabilized Sn2+ ions to form the intermediate complex, which retards the crystallization and oxidation of Sn-PVK films. Consequently, the power conversion efficiencies of devices increase from 11.0% to 12.9% with less recombination and a lower leakage current, and the stability of the devices is improved simultaneously.

Impurity Level-Induced Broadband Photoelectric Response in Wide-Bandgap Semiconductor SrSnO3.

Broadband spectrum detectors exhibit great promise in fields such as multispectral imaging and optical communications. Despite significant progress, challenges like materials instability in such devices, complex manufacturing process, and high cost still hinder their further application. Here, we present a method that achieves broadband spectral detection by impurity-level in SrSnO3. We report over 500 mA/W photoresponsivity at 275 nm (ultraviolet C solar-bind) and 367 nm (ultraviolet A) and ∼60 mA/W photoresponsivity at 532 and 700 nm (visible) with a voltage bias of -5 V. Further transport and photoluminescence results reveal a new phase transition at 88 K, which would significantly affect the impurity level of the La-doped SrSnO3 film, indicating that the broadband response attributes to the impurity levels and mutual interactions. Additionally, the photodetector demonstrates excellent robustness and stability under repeated tests and prolonged exposure in air. These findings show the potential of SrSnO3 as a material for photodetectors and propose a method to achieve broadband spectrum detection, creating new possibility for the development of single-phase, low-cost, simple structure, and high-efficiency photodetectors.

Design and optimization of zero-carbon integrated energy system for highway service area

Abstract The challenge of achieving dual-carbon targets arises from the issue of high carbon emissions in Chinese highway service areas. To address this, a comprehensive electric-thermal-hydrogen energy system is proposed, consisting of a new energy generation system, heat pumps, electrolyzers, hydrogen fuel cells, energy storage devices, and charging stations. A dispatch model for the integrated energy system is established, with the objective of minimizing the total operating cost while satisfying the constraints of each device and the electric-thermal-hydrogen balance. The model is implemented in MATLAB, and the ideal optimal solution for each decision variable is obtained using the Gurobi solver. The investment and operating costs, as well as the scheduling results for electricity, heat, and cooling, are analyzed. The results indicate that the electrolyzer-fuel cell system can improve the system’s operational stability and flexibility in dispatch optimization. Due to the instability of photovoltaic and wind power devices and the fluctuating nature of loads, energy storage devices are required for peak load shaving in the system. The zero-carbon integrated energy system model can calculate the most economical investment plan based on the load and meteorological conditions of different service areas.

Ion Migration in Metal Halide Perovskites: Characterization Protocols and Physicochemical Mechanisms.

Metal halide perovskites (MHPs) have demonstrated considerable promise for a range of photoelectronic applications owing to their prominent photophysical properties. However, MHPs suffer from remarkable ion migration under illumination and bias voltage, which generally poses operational instability of MHP-based devices and restricts their practicality. While numerous chemical strategies have been proposed for manipulating ion migration dynamics, the relevant mechanistic research relatively lags behind, which is nevertheless imperative for guiding ion migration engineering. In this perspective, we first review the well-established experimental techniques for characterizing ion migration in MHP films and photovoltaic devices. For the sake of gaining insights into the underlying mechanism, we also present a series of physical models that elucidate the dynamics of ion migration and the coupling interaction between ions and charge carriers in MHP photovoltaics. Finally, we identify several crucial areas for future investigation, with the aim of advancing both the fundamental and applied research on high-efficiency and high-stability MHP materials and devices.

Preventive Effect of Ultraviolet Photofunctionalization on Peri-implant Biofilm Formation: An In vivo Randomized Study.

Peri-implant biofilm formation due to local bacterial colonization is one of the important factors for the instability of temporary anchorage devices (TADs). The aim of this study was to quantify and compare the colonization of Streptococcus sanguinis on ultraviolet (UV) treated and untreated titanium TADs. This prospective, in vivo study included 20 subjects requiring orthodontic treatment with first premolar extraction, followed by retraction of the anterior teeth with absolute anchorage using TADs. TADs were placed interdentally, in the keratinized tissue between the upper second premolar and the first molar on the buccal side, at the mucogingival junction. It was a split-mouth study where one side of TAD was UV-treated for 15 min, and the other side was kept untreated as a control. TADs were removed after 6 months for S. sanguinis quantification on both sides and were compared for biofilm reduction. Statistical software was used to perform unpaired t-tests for the individual samples as well as for comparing total UV-treated and untreated samples. P <0.05 was considered significant. The mean bacterial count (per ml) was found to be 2.2 × 106 copy numbers and 8.9 × 106 copy numbers in the UV group and untreated group, respectively. The total count of bacteria was found to be less in the UV-treated group compared to the untreated group. The study concludes that UV photofunctionalization results in a significant reduction of S. sanguinis colony on TADs with reduced chances of failure due to inflammation.

P‐165: Method for Verifying Polyimide Charging Effect of Flexible Display

Flexible devices fabricated on polyimide (PI) substrates can be bended, rolled and folded and have a wide range of applications. However, the technical problems of the panel fabricated on the PI substrate include device instability and image sticking due to mobile charge. In this study, we introduce a method that can easily and quickly verify mobile charge in PI. Using the existing capacitance‐voltage (C‐V) measurement method, it is possible to extract the amount of mobile charges of PI existing at the bottom of the active layer. We found that the mobile charge in the PI represents the reliability and persistence of the panel. It is shown that capacitacne fluctuations of metal‐insulator‐metal semiconductor capacitors can predict image sticking of the panel. The PI charging evaluation method proposed in this study can initailly identify defects in the early stage when there is a change in the steps or procedurres of the manufacturing panel, and opens the way to accelerate research on multi‐purpose form factors in the future.

Eliminating the Adverse Impact of Composition Modulation in Perovskite Light-Emitting Diodes toward Ultra-High Brightness and Stability.

Excess ammonium halides as composition additives are widely employed in perovskite light-emitting diodes (PeLEDs), aiming to achieve high performance by controlling crystallinity and passivating defects. However, an in-depth understanding of whether excess organoammonium components affect the film physical/electrical properties and the resultant device instability is still lacking. Here, the trade-off between the performance and stability in high-efficiency formamidinium lead iodide (FAPbI3)-based PeLEDs with excess ammonium halides is pointed, and the underlying mechanism is explored. Systematic experimental and theoretical studies reveal that excess halide salt-induced ion-doping largely alters the PeLEDs properties (e.g., carrier injection, field-dependent ion-drifting, defect physics, and phase stability). A surface clean assisted cross-linking strategy is demonstrated to eliminate the adverse impact of composition modulation and boost the operational stability without sacrificing the efficiency, achieving a high efficiency of 23.6%, a high radiance of 964 W sr-1 m-2 (The highest value for FAPbI3 based PeLEDs), and a prolong lifetime of 106.1 h at large direct current density (100mA cm-2), concurrently. The findings uncovered an important link between excess halide salts and the device performance, providing a guideline for rational design of stable, bright, and high efficiency PeLEDs.

How can we improve the stability of organic solar cells from materials design to device engineering?

AbstractAmong a promising photovoltaic technology for solar energy conversion, organic solar cells (OSCs) have been paid much attention, of which the power conversion efficiencies (PCEs) have rapidly surpassed over 20%, approaching the threshold for potential applications. However, the device stability of OSCs including storage stability, photostability and thermal stability, remains to be an enormous challenge when faced with practical applications. The major causes of device instability are rooted in the poor inherent properties of light‐harvesting materials, metastable morphology, interfacial reactions and highly sensitive to external stresses. To get rid of these flaws, a comprehensive review is provided about recent strategies and methods for improving the device stability from active layers, interfacial layers, device engineering and encapsulation techniques for high‐performance OSC devices. In the end, prospectives for the next stage development of high‐performance devices with satisfactory long‐term stability are afforded for the solar community.

MSLTE: multiple self-supervised learning tasks for enhancing EEG emotion recognition

Objective. The instability of the EEG acquisition devices may lead to information loss in the channels or frequency bands of the collected EEG. This phenomenon may be ignored in available models, which leads to the overfitting and low generalization of the model. Approach. Multiple self-supervised learning tasks are introduced in the proposed model to enhance the generalization of EEG emotion recognition and reduce the overfitting problem to some extent. Firstly, channel masking and frequency masking are introduced to simulate the information loss in certain channels and frequency bands resulting from the instability of EEG, and two self-supervised learning-based feature reconstruction tasks combining masked graph autoencoders (GAE) are constructed to enhance the generalization of the shared encoder. Secondly, to take full advantage of the complementary information contained in these two self-supervised learning tasks to ensure the reliability of feature reconstruction, a weight sharing (WS) mechanism is introduced between the two graph decoders. Thirdly, an adaptive weight multi-task loss (AWML) strategy based on homoscedastic uncertainty is adopted to combine the supervised learning loss and the two self-supervised learning losses to enhance the performance further. Main results. Experimental results on SEED, SEED-V, and DEAP datasets demonstrate that: (i) Generally, the proposed model achieves higher averaged emotion classification accuracy than various baselines included in both subject-dependent and subject-independent scenarios. (ii) Each key module contributes to the performance enhancement of the proposed model. (iii) It achieves higher training efficiency, and significantly lower model size and computational complexity than the state-of-the-art (SOTA) multi-task-based model. (iv) The performances of the proposed model are less influenced by the key parameters. Significance. The introduction of the self-supervised learning task helps to enhance the generalization of the EEG emotion recognition model and eliminate overfitting to some extent, which can be modified to be applied in other EEG-based classification tasks.

Ferroelectric memory devices using hafnium aluminum oxides and remote plasma-treated electrodes for sustainable energy-efficient electronics

In this work, we adopt a low-temperature sustainable plasma treatment approach for the fabrication of ferroelectric memory devices. From our experimental results, we found that the ferroelectric polarization characteristics of HfAlOx ferroelectric device could be further improved by using low-temperature nitrogen plasma treatment on bottom TiN electrode for surface modification. The low-temperature nitrogen plasma treatment on TiN bottom electrode not only prevent electrode oxidation, but also lowers the generation of defect traps at the interface between ferroelectric HfAlOx and TiN bottom electrode during high-temperature ferroelectric annealing process. Besides, the nitrogen-treated bottom electrode also can improve bias-stress induced instability and cycling endurance of HfAlOx ferroelectric devices due to the effective suppression of randomly distributed defect traps or oxygen vacancies near the surface of bottom electrode.

On the Saturation of the Instability of Induced Ordinary Microwave Scattering in the Edge Transport Barrier of a Tokamak during Electron Cyclotron Resonance Heating of a Plasma

The saturation of the low-threshold parametric decay instability of an ordinary wave during electron cyclotron resonance heating in the edge transport barrier of a tokamak due to the stochastic damping of a daughter two-dimensionally localized oblique Langmuir wave has been considered. It has been found that the saturation of instability in modern devices occurs at a relatively low level and does not affect the energy balance during plasma heating. It has been shown that the efficiency of nonlinear pump under expected conditions of microwave power injection in the International Thermonuclear Experimental Reactor will exceed the maximum efficiency of stochastic damping, which will result in the breaking of amplitude-dependent saturation and can significantly modify the power deposition profile.

The gyrokinetic dispersion relation of microtearing modes in collisionless toroidal plasmas

We solve the linearized gyrokinetic equation, quasineutrality condition and Ampere's law to obtain the dispersion relation of microtearing modes (MTMs) in collisionless low- $\beta$ toroidal plasmas. Consistent with past studies, we find that MTMs are driven unstable by the electron temperature gradient and that this instability drive is mediated by magnetic drifts. The dispersion relation that we derive can be evaluated numerically very quickly and may prove useful for devising strategies to mitigate MTM instability in fusion devices.

Origin of the High Density of Oxygen Vacancies at the Back Channel of Back-Channel-Etched a-InGaZnO Thin-Film Transistors.

This study reveals the pronounced density of oxygen vacancies (Vo) at the back channel of back-channel-etched (BCE) a-InGaZnO (a-IGZO) thin-film transistors (TFTs) results from the sputtered deposition rather than the wet etching process of the source/drain metal, and they are distributed within approximately 25 nm of the back surface. Furthermore, the existence and distribution depth of the high density of Vo defects are verified by means of XPS spectra analyses. Then, the mechanism through which the above Vo defects lead to the instability of BCE a-IGZO TFTs is elucidated. Lastly, it is demonstrated that the device instability under high-humidity conditions and negative bias temperature illumination stress can be effectively alleviated by etching and thus removing the surface layer of the back channel, which contains the high density of Vo defects. In addition, this etch method does not cause a significant deterioration in the uniformity of electrical characteristics and is quite convenient to implement in practical fabrication processes. Thus, a novel and effective solution to the device instability of BCE a-IGZO TFTs is provided.

Genetically stable kill-switch using "demon and angel" expression construct of essential genes.

Genetic instability of synthetic genetic devices is a key obstacle for practical use. This problem is particularly critical in kill-switches for conditional host killing. Here, we propose a genetically stable kill-switch based on a "demon and angel" expression construct of a toxic essential gene. The kill-switch conditionally overexpresses the toxic essential gene. Additionally, the identical essential gene is deleted in the genome. The essential gene is expressed at a low level to maintain host survival in the OFF state and kills the host by the overexpression in the ON state. The single expression construct is responsible for both killing the hosts and maintaining viability, reducing the emergence of loss-of-function mutants. We constructed the kill-switch using the toxic essential gene encoding tyrosyl-tRNA synthetase, tyrS, in Escherichia coli. The bacteria harboring the kill-switch were conditionally suicidal over 300 generations. Toxic overexpression of essential genes has also been found in other organisms, suggesting that the "demon and angel" kill switch is scalable to various organisms.

Mathematical Modeling and Optimization of Highly Efficient Nontoxic All-Inorganic CsSnGeI3-Based Perovskite Solar Cells with Oxide and Kesterite Charge Transport Layers.

Despite exceptional optoelectronic properties and rapidly increasing efficiency of perovskite solar cells (PSCs), the issues of toxicity and device instability have hampered the commercialization of this renewable energy technology. Lead (Pb) being the main culprit creates major environmental risks and therefore must be replaced with a nontoxic material such as tin (Sn), germanium (Ge), etc. Moreover, replacing organic cations in the perovskite's ABX3 structure with inorganic ones like cesium (Cs) helps aid the stability issues. This study uses six different kesterite-based hole transport layers (HTLs) and three different metal oxide-based electron transport layers (ETLs) to numerically simulate and optimize all-inorganic CsSnGeI3 PSCs. Metal oxide ETLs are used in this study due to their large band gap, while kesterite HTLs are used due to their excellent conductive properties. All of the simulations are performed under standard testing conditions. A total of 18 novel planar (n-i-p) PSCs are modeled by the combination of various charge transport layers (CTLs), and the device optimization was done to enhance the power conversion efficiencies (PCEs) of the PSCs. Furthermore, the effect of CTLs on the energy band alignment, electric field, quantum efficiency, light absorption, and recombination rate is analyzed. Additionally, a detailed analysis of the impact of defect density (Nt), interface defects (ETL/Perv, Perv/HTL), temperature, and work function on the functionality of 18 different CsSnGeI3-based PSCs is conducted. The simulation findings demonstrate that SnO2/CsSnGeI3/CNTS is the most efficient optimized PSC among all of the simulated structures, with a PCE of 27.33%, Jsc of 28.04 mA/cm2, FF of 85%, and Voc of 1.14 V.