30 research outputs found
Amplification trojan network: Attack deep neural networks by amplifying their inherent weakness
Recent works found that deep neural networks (DNNs) can be fooled by
adversarial examples, which are crafted by adding adversarial noise on clean
inputs. The accuracy of DNNs on adversarial examples will decrease as the
magnitude of the adversarial noise increase. In this study, we show that DNNs
can be also fooled when the noise is very small under certain circumstances.
This new type of attack is called Amplification Trojan Attack (ATAttack).
Specifically, we use a trojan network to transform the inputs before sending
them to the target DNN. This trojan network serves as an amplifier to amplify
the inherent weakness of the target DNN. The target DNN, which is infected by
the trojan network, performs normally on clean data while being more vulnerable
to adversarial examples. Since it only transforms the inputs, the trojan
network can hide in DNN-based pipelines, e.g. by infecting the pre-processing
procedure of the inputs before sending them to the DNNs. This new type of
threat should be considered in developing safe DNNs.Comment: Published Sep 2022 in Neurocomputin
Language-Driven Anchors for Zero-Shot Adversarial Robustness
Deep neural networks are known to be susceptible to adversarial attacks. In
this work, we focus on improving adversarial robustness in the challenging
zero-shot image classification setting. To address this issue, we propose LAAT,
a novel Language-driven, Anchor-based Adversarial Training strategy. LAAT
utilizes a text encoder to generate fixed anchors (normalized feature
embeddings) for each category and then uses these anchors for adversarial
training. By leveraging the semantic consistency of the text encoders, LAAT can
enhance the adversarial robustness of the image model on novel categories
without additional examples. We identify the large cosine similarity problem of
recent text encoders and design several effective techniques to address it. The
experimental results demonstrate that LAAT significantly improves zero-shot
adversarial performance, outperforming previous state-of-the-art adversarially
robust one-shot methods. Moreover, our method produces substantial zero-shot
adversarial robustness when models are trained on large datasets such as
ImageNet-1K and applied to several downstream datasets.Comment: 11 page
High-throughput surface preparation for flexible slot die coated perovskite solar cells
To achieve industrially viable fabrication process for perovskite-based solar cells, every process step must be optimized for maximum throughput. We present a study of substituting laboratory-type UV-Ozone surface treatment with a high-throughput Corona treatment in a scalable perovskite solar cell fabrication process. It is observed that water contact angle measurements provide insufficient information to determine the necessary dose of Corona or UV-Ozone treatment, but the surface carbon signal measured by x-ray photoelectron spectroscopy accurately identifies when surface contamination has been completely removed. Furthermore, we observe highly accelerated de-contamination of ZnO surfaces by UV-Ozone treatment. The effect can be explained by photocatalytic O-2(-) ion generation indicating that UV-Ozone treatment is also applicable in high-throughput processing
CsPbBrxI3-x thin films with multiple ammonium ligands for low turn-on pure-red perovskite light-emitting diodes
All-inorganic α-CsPbBrxI3-x perovskites featuring nano-sized crystallites show great potential for pure-red light-emitting diode (LED) applications. Currently, the CsPbBrxI3âx LEDs based on nano-sized α-CsPbBrxI3-x crystallites have been fabricated mainly via the classical colloidal route including a tedious procedure of nanocrystal synthesis, purification, ligand or anion exchange, film casting, etc. With the usually adopted conventional LED device structure, only high turn-on voltages (> 2.7) have been achieved for CsPbBrxI3-x LEDs. Moreover, this mix-halide system may suffer from severe spectra-shift under bias. In this report, CsPbBrxI3-x thin films featuring nano-sized crystallites are prepared by incorporating multiple ammonium ligands in a one-step spin-coating route. The multiple ammonium ligands constrain the growth of CsPbBrxI3-x nanograins. Such CsPbBrxI3-x thin films benefit from quantum confinement. The corresponding CsPbBrxI3-x LEDs, adopting a conventional LED structure of indium-doped tin oxide (ITO)/poly(3,4-ethylenedioxythiophene):poly(styrenesulfonate) (PEDOT:PSS)/CsPbBrxI3-x/[6, 6]-phenyl C61 butyric acid methyl ester (PCBM)/bathocuproine (BCP)/Al, emit pure-red color at Commission Internationale de lâĂ©clairage (CIE) coordinates of (0.709, 0.290), (0.711, 0.289), etc., which represent the highest color-purity for reported pure-red perovskite LEDs and meet the Rec. 2020 requirement at CIE (0.708, 0.292) very well. The CsPbBrxI3-x LED shows a low turn-on voltage of 1.6 V, maximum external quantum efficiency of 8.94%, high luminance of 2,859 cdmâ2, and good color stability under bias
Engineering Green-to-Blue Emitting CsPbBr3 Quantum-Dot Films with Efficient Ligand Passivation
A series of challenging issues such as field-driven spectral drift for the CsPbClxBr3âx system and mixed phases in quasi-two-dimensional structures still exist when devising blue-emitting perovskites. In this Letter, the CsPbBr3 quantum-dot (QD) system is proposed to overcome these challenges. However, to date, the CsPbBr3 QD films with tunable colors from green to blue still cannot be achieved using existing methods. Herein, a simple one-step spin-coating route incorporated with efficient ligand passivation is developed to realize this goal. The size restriction of CsPbBr3 QDs is enabled by a diammonium ligand, propane-1,3-diammonium bromide (PDAB). A mixed-ligand system of phenethylammonium bromide (PEAB) with PDAB is further explored to enhance their optical performance. The CsPbBr3 QDs experience a second growth process upon controlled air exposure, which is utilized to realize their size control and emission wavelength tunability. The CsPbBr3 QD-based devices exhibit no spectral drift in electroluminescence under voltage bias
Reduction of lead leakage from damaged lead halide perovskite solar modules using self-healing polymer-based encapsulation
In recent years, the major factors that determine commercialization of perovskite photovoltaic technology have been shifting from solar cell performance to stability, reproducibility, device upscaling and the prevention of lead (Pb) leakage from the module over the device service life. Here we simulate a realistic scenario in which perovskite modules with different encapsulation methods are mechanically damaged by a hail impact (modified FM 44787 standard) and quantitatively measure the Pb leakage rates under a variety of weather conditions. We demonstrate that the encapsulation method based on an epoxy resin reduces the Pb leakage rate by a factor of 375 compared with the encapsulation method based on a glass cover with an ultraviolet-cured resin at the module edges. The greater Pb leakage reduction of the epoxy resin encapsulation is associated with its optimal self-healing characteristics under the operating conditions and with its increased mechanical strength. These findings strongly suggest that perovskite photovoltaic products can be deployed with minimal Pb leakage if appropriate encapsulation is employed
The Impact of Atmosphere on Energetics of Lead Halide Perovskites
Solar cells based on metal halide perovskites have emerged as a promising low-cost photovoltaic technology. In contrast to inert atmospheres where most of the lab-scale devices are made to date, large-area low-cost production of perovskite solar cells often involves processing of perovskites in various atmospheres including ambient air, nitrogen, and/or vacuum. Herein, the impact of atmosphere on the energy levels of methylammonium lead halide perovskite films is systematically investigated. The atmosphere is varied to simulate the typical fabrication process. Through a comprehensive analysis combining the Fermi level evolution, surface photovoltage, photoluminescence properties, photovoltaic performance, and device simulation, an overall landscape of the energy diagram of the perovskite layer is able to be determined. The findings have direct implications for real-world devices under typical atmospheres, and provide insights into the fabrication-process design and optimization. Furthermore, a universal Fermi level shift under vacuum for lead halide-based perovskites revealed in this study, urges a refreshed view on the energetics studies conducted without considering the atmospheric effect
NegligibleâPbâWaste and Upscalable Perovskite Deposition Technology for HighâOperationalâStability Perovskite Solar Modules
An upscalable perovskite film deposition method combining raster ultrasonic spray coating and chemical vapor deposition is reported. This method overcomes the coating size limitation of the existing stationary spray, singleâpass spray, and spinâcoating methods. In contrast with the spinâcoating method (>90% Pb waste), negligible Pb waste during PbI2 deposition makes this method more environmentally friendly. Outstanding film uniformity across the entire area of 5 cm Ă 5 cm is confirmed by both largeâarea compatible characterization methods (electroluminescence and scattered light imaging) and local characterization methods (atomic force microscopy, scanning electron microscopy, photoluminescence mapping, UVâvis, and Xâray diffraction measurements on multiple sample locations), resulting in low solar cell performance decrease upon increasing device area. With the FAPb(I0.85Br0.15)3 (FA = formamidinium) perovskite layer deposited by this method, champion solar modules show a power conversion efficiency of 14.7% on an active area of 12.0 cm2 and an outstanding shelf stability (only 3.6% relative power conversion efficiency decay after 3600 h aging). Under continuous operation (1 sun light illumination, maximum power point condition, dry N2 atmosphere with <5% relative humidity, no encapsulation), the devices show high lightâsoaking stability corresponding to an average T80 lifetime of 535 h on the smallâarea solar cells and 388 h on the solar module
Highly Efficient and Stable Perovskite Solar Cells via Modification of Energy Levels at the Perovskite/Carbon Electrode Interface
Perovskite solar cells (PSCs) have attracted great attention in the past few years due to their rapid increase in efficiency and low-cost fabrication. However, instability against thermal stress and humidity is a big issue hindering their commercialization and practical applications. Here, by combining thermally stable formamidinium-cesium-based perovskite and a moisture-resistant carbon electrode, successful fabrication of stable PSCs is reported, which maintain on average 77% of the initial value after being aged for 192 h under conditions of 85 degrees C and 85% relative humidity (the "double 85" aging condition) without encapsulation. However, the mismatch of energy levels at the interface between the perovskite and the carbon electrode limits charge collection and leads to poor device performance. To address this issue, a thin-layer of poly(ethylene oxide) (PEO) is introduced to achieve improved interfacial energy level alignment, which is verified by ultraviolet photoemission spectroscopy measurements. Indeed as a result, power conversion efficiency increases from 12.2% to 14.9% after suitable energy level modification by intentionally introducing a thin layer of PEO at the perovskite/carbon interface
Mechanism, prevention and treatment of cognitive impairment caused by high altitude exposure
Hypobaric hypoxia (HH) characteristics induce impaired cognitive function, reduced concentration, and memory. In recent years, an increasing number of people have migrated to high-altitude areas for work and study. Headache, sleep disturbance, and cognitive impairment from HH, severely challenges the physical and mental health and affects their quality of life and work efficiency. This review summarizes the manifestations, mechanisms, and preventive and therapeutic methods of HH environment affecting cognitive function and provides theoretical references for exploring and treating high altitude-induced cognitive impairment