Active Layer Thickness Research Articles

Enhancing light absorption in ultra-thin perovskite solar cells using plasmonic gold nanoparticle clusters

Perovskite solar cells with ultra-thin absorber layers offer potential cost savings in manufacturing, but their reduced thickness can limit light absorption and efficiency. This work explores using plasmonic gold nanoparticles as a light-trapping strategy to compensate for lower absorption in ultra-thin perovskite devices. Numerical simulations investigate embedding 25 nm radius gold nanoparticles within the 200 nm thick perovskite active layer to boost optical absorption through near-field enhancement and light scattering effects. The solar cell structure incorporating these plasmonic nanoparticles achieves a substantially higher short-circuit current density of 23.10 mA cm−2 compared to 18.70 mA cm−2 for a reference cell without nanoparticles. This study provides design approaches for realizing high-efficiency yet cost-effective ultra-thin perovskite photovoltaics by harnessing plasmonic light-trapping techniques. The results display methodologies to improve photon absorption and power conversion in thin-film perovskite devices through strategic nanoparticle integration.

Carboxyl-functionalized polyimide for polar/non-polar organic solvent separation by pervaporation

The separation of azeotropic organic-organic mixtures is critical in the chemical and petrochemical sectors and membrane technology is one of the most successful and sustainable ways to achieve it. A significant challenge is to find materials with the adequate permselectivity for the demanding operational conditions. We propose a carboxyl-functionalized polyimide for pervaporation and separation of polar and non-polar organic azeotropic mixtures with high industrial relevance, such as methanol-toluene, methanol/methyl tert-butyl ether, and ethanol-cyclohexane. Both flat dense films and hollow fibers were investigated. The fabrication as hollow fibers enabled the flux increase by reducing the active layer thickness from 40 to 0.3 μm, while keeping the separation factors nearly unchanged. For methanol/toluene mixtures, by using hollow fibers, the separation factor was around 140, with a flux of 0.54 kg m−2 h−1. For methanol/methyl tert-butyl ether, the separation factor was around 3100 with a flux of 0.14 kg m−2 h−1. For ethanol/cyclohexane, the separation factor was 406 with a flux of 0.24 kg m−2 h−1. The pervaporation performance is a result of a combination of the membrane adequate hydrophilicity and robust mechanical stability, demonstrating their potential application for separating alcohols from organic mixtures.

High-precision estimation of pan-Arctic soil surface temperature from MODIS LST by incorporating multiple environment factors and monthly-based modeling

Global warming has shown an “Arctic amplification effect” in recent decades, leading to pronounced changes in pan-Arctic soil surface temperature (SST). SST plays a direct role in energy exchange between soil and atmosphere and serves as an indicator of the land–atmosphere energy balance. Remote sensing land surface temperature (LST) data is able to indicate near-surface temperature, but influences from environment factors, such as vegetation and snow, can introduce biases between LST and SST. In this study, the importances of five environment factors (vegetation, snow, surface soil composition, topography, and solar radiation) to monthly mean SST estimation from MODIS LST in pan-Arctic were analyzed. Then a method for pan-Arctic monthly mean SST estimation from MODIS LST by incorporating these environment factors and monthly-based modeling based on random forest (RF) algorithm was proposed. The results reveal that all the selected environment factors contribute to monthly-based modeling, with vegetation exerting the greatest importance from May to October and snow in March and April. The root mean square error (RMSE) of pan-Arctic monthly SST estimated by the proposed method from 2003 to 2022 ranges from 0.89 to 1.88 °C, which is a 42.95–––53.35 % reduction compared to the widely used season-based multivariate linear regression (MLR) models based solely on LST (RMSE between 1.56 and 4.03 °C). The accuracy is notably improved in areas with lower and no vegetation (grassy woodlands, grasslands, permanent wetlands, and barrens) in the cold season (September to the following April), and in higher vegetation (forests) areas in the warm season (May to August). The proposed method can contribute to producing high-precision monthly mean SST data from LST, estimating permafrost extent and active layer thickness, and understanding the land–atmosphere energy balance in pan-Arctic.

Investigation of BGaN Layer in Photodetector Structure

This study involves the design and simulation of a BGaN/GaN/ZnO/Al2O3 photodetector for UV/BLUE light with two different boron concentrations: 5% and 20%. The proposed photodetector structure exhibits an internal optical gain of 3.867 × 104 at 10 V and a wavelength of 250 nm for x = 0.05. Moreover, a gain of 1.006 × 104 at the same voltage and wavelength was obtained for a 20% boron concentration under an incidence of 0.01 × 104 cm2/W. A photocurrent peak of 0.31 mA at a wavelength of 0.455 µm, corresponding to an energy of 2.73 eV, was achieved for x = 0.05, which makes it a promising candidate for optoelectronic devices, such as light-emitting diodes (LEDs). A maximum photocurrent of 0.54 mA in the long-range deep UV range between 100 and 250 nm was obtained for x = 0.2. Based on the simulated spectral response, increasing the band gap (EG) improves the optical absorption, and higher absorption rates were found at x = 0.2 in the UV area. However, we also considered the impact of the BGaN active layer thickness on dark current and photocurrent at room temperature. Additionally, we studied the effect of temperature on current under illumination.

Toward long-term monitoring of regional permafrost thaw with satellite interferometric synthetic aperture radar

Abstract. Active-layer thickness (ALT) is estimated for a study area in northern Alaska's continuous-permafrost zone using satellite data from Sentinel-1 (radar) and ICESat-2 (lidar) for the period 2017 to 2022. Synthetic aperture radar (SAR) interferograms were generated using the Short Baseline Subset (SBAS) approach. Displacement time series over the thaw season (June–September) are fit well with a linear model (root mean square error (RMSE) scatter is less than 7 mm) and show maximum seasonal subsidence of 20–60 mm. ICESat-2 products were used to validate the interferometric synthetic aperture radar (InSAR) displacement time series. ALT was estimated from measured subsidence using a widely used model exploiting the volume difference between ice and water, reaching a maximum depth in our study area of 1.5 m. Estimated ALT is in good agreement with in situ and other remotely sensed data but is sensitive to assumed thaw season onset, indicating the need for reliable surface temperature data. Our results suggest the feasibility of long-term permafrost monitoring with satellite InSAR. However, the C-band (∼55 mm center wavelength) Sentinel radar is sensitive to vegetation cover and, in our studies, was not successful for similar monitoring in the heavily treed discontinuous-permafrost zone of central Alaska.

The surface deformation of permafrost and active layer thickness in the upper reaches of the Black River basin, revealed by InSAR observations and independent component analysis

The Heihe River Basin, located in the northeastern part of the Qinghai-Tibetan Plateau, is part of the perennial permafrost belt of the Qilian Mountains. Recent observations indicate ongoing permafrost degradation in this region. This study utilizes data from 255 observations provided by Sentinel-1 satellites, MODIS Land Surface Temperature, SMAP-L4 soil moisture data, GNSS measurements, and in situ measurement. We introduced Variational Bayesian independent Component Analysis (VB-ICA) in multi-temporal Interferometric Synthetic Aperture Radar (MT-InSAR) processing to investigate the spatial-temporal characteristics of surface deformation and permafrost active layer thickness (ALT) variations. The analysis demonstrates strong agreement with borehole data and offers improvements over traditional methodologies. The maximum value of ALT in the basin is found to be 5.7 m. VB-ICA effectively delineates seasonal deformations related to the freeze-thaw cycles, with a peak seasonal deformation amplitude of 60 mm. Moreover, the seasonal permafrost's lower boundary reaches an elevation of 3700 m, revealing that permafrost is experiencing widespread degradation and associated soil erosion in the high elevation region of The Heihe River Basin. The paper also explores the efficacy of reference point selection and baseline network establishment for employing the InSAR method in monitoring freeze-thaw deformations. The study underscores the InSAR method's adaptability and its importance for interpreting permafrost deformation and related parameters.

High-temperature planar asymmetric ceramic membranes: Effect of the Pt amount and dispersion on the H2 separation performance

This work investigates for the first time the effect of Pt catalyst amount and dispersion on hydrogen permeation performances of BaCe0.65Zr0.20Y0.15O3−δ–Gd0.2Ce0.8O2−δ (BCZY–GDC) composite planar Cer-Cer membranes with asymmetrical architecture, aiming to maximize the ratio between the permeated hydrogen and the metal content. To boost the hydrogen separation reactions, Pt must be deposited on both the dense and porous sides of the membrane. Moreover, the complex architecture of the porous layer can be used to disperse Pt particles providing a good interaction with the membrane. To fulfil this aim BCZY-GDC membranes composed of a 20 μm thick active dense layer and a 600 μm thick, porous support were produced by tape casting and impregnated with different amounts of platinum. Hydrogen permeation properties were thoroughly investigated examining the composition of the feed and the sweep gasses, temperature, stream humidification, catalyst amount and nature of the dispersion media. The effect of Pt-catalysed hydrogen permeation and water splitting reaction at the permeate side was investigated and discussed. It was found that using an optimal amount of Pt solution to activate the porous side of the membranes is paramount to increase hydrogen permeation in the whole operating temperature range while keeping low the amount of noble metal catalyst. Moreover, the selection of a proper solvent with good interaction with the membrane allows the obtainment of smaller Pt nanoparticles resulting in higher permeation. The best performances in terms of hydrogen permeation (0.74 and 1.29 mL min−1 cm−2 at 750 °C using a feed stream with respectively 50 % and 80 % of H2 in He) were obtained using an acetone-based solution for depositing 1.5 mg cm−2 of Pt at the porous side. This work suggests that the metal deposition plays a non-trivial role in the hydrogen separation process and should be fully evaluated to increase the final performance while cutting down the cost of the Pt catalyst and therefore, of the final device.

Enhancing Blue Polymer Light-Emitting Diode Performance by Optimizing the Layer Thickness and the Insertion of a Hole-Transporting Layer.

Polymer light-emitting diodes (PLEDs) hold immense promise for energy-efficient lighting and full-color display technologies. In particular, blue PLEDs play a pivotal role in achieving color balance and reducing energy consumption. The optimization of layer thickness in these devices is critical for enhancing their efficiency. PLED layer thickness control impacts exciton recombination probability, charge transport efficiency, and optical resonance, influencing light emission properties. However, experimental variations in layer thickness are complex and costly. This study employed simulations to explore the impact of layer thickness variations on the optical and electrical properties of blue light-emitting diodes. Comparing the simulation results with experimental data achieves valuable insights for optimizing the device's performance. Our findings revealed that controlling the insertion of a layer that works as a hole-transporting and electron-blocking layer (EBL) could greatly enhance the performance of PLEDs. In addition, changing the active layer thickness could optimize device performance. The obtained results in this work contribute to the development of advanced PLED technology and organic light-emitting diodes (OLEDs).

SILAR deposition and characterization of ZnO films for numerical investigation as electron transport layer in solar cells

The SILAR method of thin film deposition has attracted the scientific community over the years due to its easiness, low cost, availability of room temperature deposition, and more over due to the variation in properties of thin films available by varying deposition parameters.This work is carried out in a way to comprehensively compare two ZnO thin film samples prepared from precursor media with Zinc Acetate (S1) and Zinc Chloride(S2) salts deposited by SILAR method in Perovskite Solar cell applications. The XRD, FTIR, Raman, FESEM, and UV-Visible analysis were carried out for identifying the structural, morphological, and optical quality of these samples. The role of these samples as Electron Transport Layer (ETL) in Perovskite Solar cell were identified using General purpose PhotoVoltaic Device model (GPVDM) simulation software which is well adapted for studying Solar cell architecture. It provided the output Solar cell parameters like Jsc, Voc, FF, PCE, etc and by varying the active layer and Hole Transport Layer (HTL) thicknesses, the optimized efficiency of devices with samples S1 and S2 were obtained as 21.88% and 21.96%.The results showed that SILAR-synthesized ZnO thin films could be potential candidates for ETL applications in Perovskite Solar cells.

Thermokarst landslides susceptibility evaluation across the permafrost region of the central Qinghai-Tibet Plateau: Integrating a machine learning model with InSAR technology

Thermokarst landslides (TLs), which are made up of retrogressive thaw slumps (RTSs) and active-layer detachments slides (ALDSs), are quickly increasing in the central Qinghai-Tibet Plateau (QTP) permafrost area. TLs induce many environmental problems and threaten the safety of infrastructure. A landslide susceptibility map is crucial to prevent the negative impacts of these landslides. However, traditional thermokarst landslides susceptibility (TLS) evaluations do not consider real-time surface deformation information. Therefore, we propose a novel method that integrates a conventional machine learning model with ground surface deformation. Nine influencing factors, including slope, normalized difference vegetation index, elevation, precipitation, thawing degree days, soil content, active layer thickness, water content, and vegetation type were selected based on the q-index detector, and support vector machine was employed to obtain an initial model (IM). We obtained surface deformation in the study area using the enhanced Small Baseline Subset (SBAS) method. The accuracy of the InSAR results was validated through comparison with data from two field monitoring cross-sections. Subsequently, we established an integrated model (ITM) by combining the initial model with surface deformation using the contribution matrix, and confirmed the fusion model’s higher rationality and accuracy through comparison with the IM. Furthermore, we examined the impact of the quadtree segmentation method on atmospheric correction and validated the TLS results obtained using the ITM with high-resolution optical remote sensing imagery from GF6. Finally, the influencing factors and distribution characteristics of TLS was analyzed, and the results indicated that climatic conditions are the primary factors affecting the distribution of TLS.

Hysteresis of Northern Hemisphere permafrost to carbon dioxide emissions

Abstract Carbon dioxide removal (CDR) is proposed to limit the level of global warming and minimize the impacts of climate crises. However, how permafrost may respond to negative carbon emissions remains unknown. Here, the response of near-surface permafrost in the Northern Hemisphere is investigated based on idealized carbon dioxide (CO2) ramp-up (284.7–1138.8 ppm) and symmetric ramp-down model experiments. The results demonstrate that the timing of the minimum permafrost area lags the maximum CO2 concentration for decades, which is also observed in soil temperatures at different depths and active layer thicknesses. When the CO2 concentration is reversed to the preindustrial level, the permafrost area decreases by ~12% relative to the initial conditions, together with additional warming in the ground temperature at the top of the permafrost, indicating the hysteresis of permafrost to CO2 removal. The most profound hysteretic responses occur at high latitudes for soil temperatures owing to Arctic amplification, while at the southern margins of the permafrost zones for permafrost and active layer thickness that largely linked to the climate state. Moreover, the sensitivity of permafrost and the associated thermodynamic factors to CO2 change is generally lower during the CO2 ramp-down phase than during the ramp-up phase, likely due to the release of stored heat on land. The results reveal the behaviour of permafrost in response to negative carbon emissions, which is informative for the projections of permafrost towards carbon neutral targets. In addition, the results may provide a reference for permafrost-related tipping points (e.g., releasing long-term stored greenhouse gases and destabilising recalcitrant soil carbon) and risk management in the future.

Performance evaluation of thin film GaSb thermophotovoltaic cells

Economical converters are the key component for the industrial applications of thermophotovoltaic technology. In this work thin film GaSb cells are demonstrated for broadband thermophotovoltaic energy conversion. It is shown that n-on-p configuration is a superior choice for thin film cell due to its larger accessible efficiency. Under the illumination of unshaped blackbody spectrum, the matched spectrum temperature for GaSb thin film cells should be in the range of 2000∼2600 K, With those matched spectra, the optimal GaSb thin film can achieve the efficiency up to 8% or so with V OC = 0.55 V, FF = 0.64, J SC = 44 A cm−2, thus showing the power density output up to 15 W cm−2 while only having the active layer thickness 4.5 μm or so. These results are well preserved for S F no more than 104 cm s−1. With increasing spectrum temperature, a phenomenological model has also been formulated to analytically predict the optimal cell structure at a given spectrum illumination. This work has thus established the fundamental guidelines to develop GaSb thin film cells or subcells for economical thermophotovoltaic energy conversion.

A Self-Assembled Multiphasic Thin Film as an Oxygen Electrode for Enhanced Durability in Reversible Solid Oxide Cells.

The implementation of nanocomposite materials as electrode layers represents a potential turning point for next-generation of solid oxide cells in order to reduce the use of critical raw materials. However, the substitution of bulk electrode materials by thin films is still under debate especially due to the uncertainty about their performance and stability under operando conditions, which restricts their use in real applications. In this work, we propose a multiphase nanocomposite characterized by a highly disordered microstructure and high cationic intermixing as a result from thin-film self-assembly of a perovskite-based mixed ionic-electronic conductor (lanthanum strontium cobaltite) and a fluorite-based pure ionic conductor (samarium-doped ceria) as an oxygen electrode for reversible solid oxide cells. Electrochemical characterization shows remarkable oxygen reduction reaction (fuel cell mode) and oxygen evolution activity (electrolysis mode) in comparison with state-of-the-art bulk electrodes, combined with outstanding long-term stability at operational temperatures of 700 °C. The disordered nanostructure was implemented as a standalone oxygen electrode on commercial anode-supported cells, resulting in high electrical output in fuel cell and electrolysis mode for active layer thicknesses of only 200 nm (>95% decrease in critical raw materials with respect to conventional cathodes). The cell was operated for over 300 h in fuel cell mode displaying excellent stability. Our findings unlock the hidden potential of advanced thin-film technologies for obtaining high-performance disordered electrodes based on nanocomposite self-assembly combining long durability and minimized use of critical raw materials.

Enhanced terahertz ISBT in GaAsBi/AlGaAs quantum well: impact of doping modulation

One of the pivotal characteristics of quantum wells (QW) designed for applications in filters or modulators is its absorption coefficient. This study investigates the combined influence of doping and active layer thickness on the absorption coefficient in GaAsBi/AlGaAs quantum wells. The self-consistent coupling between Schrödinger and Poisson equations was employed for this purpose. A comprehensive analysis of conduction band structure, energy levels, potentials, and densities is presented. This analysis discerns the effects of doping on intersubband transitions (ISBTs) in the terahertz (THz) frequency domain. An introduction of a donor impurity into the system greatly influenced the intersubband absorption coefficient, increasing its intensity and causing the optical response to shift toward the lowest frequency. The obtained resonant peak energies, situated within the terahertz spectrum, hint at promising applications for GaAsBi-based devices within this frequency band.

High Arctic Vegetation Communities With a Thick Moss Layer Slow Active Layer Thaw

AbstractSvalbards permafrost is thawing as a direct consequence of climate change. In the Low Arctic, vegetation has been shown to slow down and reduce the active layer thaw, yet it is unknown whether this also applies to High Arctic regions like Svalbard where vegetation is smaller, sparser, and thus likely less able to insulate the soil. Therefore, it remains unknown which components of High Arctic vegetation impact active layer thaw and at which temporal scale this insulation could be effective. Such knowledge is necessary to predict and understand future changes in active layer in a changing Arctic. In this study we used frost tubes placed in study grids located in Svalbard with known vegetation composition, to monitor the progression of active layer thaw and analyze the relationship between vegetation composition, vegetation structure and snow conditions, and active layer thaw early in summer. We found that moss thickness, shrub and forb height, and vascular vegetation cover delayed soil thaw immediately after snow melt. These insulating effects attenuated as thaw progressed, until no effect on thaw depth was present after 8 weeks. High Arctic mosses are expected to decline due to climate change, which could lead to a loss in insulating capacity, potentially accelerating early summer active layer thaw. This may have important repercussions for a wide range of ecosystem functions such as plant phenology and decomposition processes.

Simulation of SnO2/Cs2AgInBr6/CuO heterojunction solar cell using AMPS-1D modeling

Using the one-dimensional computer code AMPS-1D MPS-1D (Analysis of Microelectronic and Photonic Structures), we simulated a lead-free double perovskite cell made of Cs2AgInBr6. This study examines the influence of the thickness and acceptor density of the active layer (Cs2AgInBr6) on key solar cell parameters, including short-circuit current density (JSC), efficiency (Eff), fill factor (FF), open-circuit voltage (VOC), current-voltage characteristics (J-V)). Our results suggest that an optimal active layer thickness of 500 nm yields good performance for the studied solar cell. Furthermore, the ideal acceptor density for enhancing output parameters is in the range of 10¹3-10¹⁵ cm⁻³. Post-optimization, our findings reveal a Voc of 0.969 V, a Jsc of 29.402 mA cm⁻², and an FF of 0.876, resulting in an efficiency of 24.959%. The results from AMPS-1D simulations for a Cs2AgInBr6 lead-free double perovskite solar cell suggest that this material and device structure can achieve high efficiency and good performance characteristics.

Inorganic charge transport layer for efficient Pb-free KSnI3 based perovskite solar cells: a theoretical study

The power conversion efficiency (PCE) of lead (Pb)-based perovskite solar cells (PSCs) is remarkably high; however, the toxicity of Pb poses a significant barrier to their commercial viability. In the current study, the effect of different charge transport layer (CTL) materials on the performance of the Pb free Sn-based (KSnI3) PSCs has been studied by using SCAPS simulations. Tin oxide (SnO2), zinc oxide, and titanium dioxide as electron transport materials, whereas spiro-OMeTAD, copper oxide (Cu2O), and nickel oxide as hole transport layer materials were iterated to achieve the optimum photovoltaic parameters. The photovoltaic parameters were optimized in terms of the active layer and CTL thicknesses, as well as the doping concentration, defect density, and interfacial defect density. Moreover, the impact of series and shunt resistance on the performance of PSCs is also investigated. The most efficient PSC with PCE of 21.75% was achieved with the device structure of FTO/SnO2/KSnI3/Cu2O. This efficiency is higher than previously reported KSnI3 based-PSCs. The SnO2 (ETL) and Cu2O were proven to be most efficient choices for the CTL materials. It was also observed that the carbon, nickel, and selenium can be a cost-effective alternative to gold for the rear contact. This study showcases how KSnI3 with inorganic charge transport layers stands as a prospective stable PSC with the potential to deliver clean, and green renewable energy solutions.

Optimization of the Active Layer Thickness for Inverted Ternary Organic Solar Cells Achieves 20% Efficiency with Simulation

Optimization of the Active Layer Thickness for Inverted Ternary Organic Solar Cells Achieves 20% Efficiency with Simulation

Atmosphere circulation patterns synchronize pan-Arctic glacier melt and permafrost thaw

The Arctic is changing rapidly due to the amplification of global temperature trends, causing profound impacts on the ice sheet in Greenland, glaciers, frozen ground, ecosystems, and societies. Here, we focus on impacts that atmospheric circulation causes in addition to the climate warming trends. We combine time series of glacier mass balance from temporal satellite gravimetry measurements (GRACE/GRACE-FO; 2002–2023), active layer thickness in permafrost areas from ESA’s Climate Change Initiative remote sensing and modelling product (2003–2019), and field measurements of the Circumpolar Active Layer Monitoring Network (2002–2023). Despite regional and system-related complexities, we identify robust covariations between these observations, which vary asynchronously between neighbouring regions and synchronously in regions antipodal to the North Pole. We reveal a close connection with dominant modes of atmosphere circulation, controlling about 75% of the common pan-Arctic impact variability (2002–2022), also affecting the Greenland Ice Sheet. We emphasize that it is necessary to consider such atmospheric driving patterns when projecting impacts, particularly caused by extremes, in an increasingly warmer Arctic.

Organic solar cell efficiency improvement through architecture engineering by integrating carbon nanoring – SCAPS 1D modelling

This research work aims to investigate on improving the performance of organic solar cells (OSC) by proposing new architectures that progressively integrate carbon nanotubes. This contribution takes into account the exceptional properties of carbon nanotubes (CNT) highlighted in recent work, with the aim of addressing the current challenges of materials used in the manufacture of conventional OSCs, such as reactivity with the ambient medium, stability over time, better transport of charge carriers, etc. Using a reference OSC cell with the following structure: PEDOT/BHJ/PDINO and the numerical one-dimensional simulation tool SCAPS, which helps in validating the modelling approach, we gradually replace each layer with a CNT-based material exhibiting superior properties. In this respect, we carry out calculations on the different cells architectures, to better visualize energy-level alignment profiles, the different current-voltage (J-V), and quantum efficiency (QE) characteristics. Approaches toward efficiency improvement were discussed, by investigating the effects of active layer thickness, the doping level, the charge carriers mobility, defect density, and external parameters such as temperature. After numerous calculations and modelling, very promising results were finally achieved with a full CNT-based solar structure with the following recorded performances: VOC=0.87V, JSC=27.81mA/cm2, FF=80.91%, and PCE=19.63%. These results are the first theoretical report for a complete CNT-based modelled OSC and, given the reliability and robustness of the approach adopted, they can be considered as relevant for future theoretical and experimental work. The integration of CNT as functional layers is a remarkable step forward in OSC architectures engineering for efficiency enhancement. CNT are good candidates for light harvesting applications.