Search Results (202)

The global transition to renewable energy has made photovoltaics a potential primary energy source, due to the abundance of solar radiation worldwide and the technological maturity of conversion systems. In this context, cadmium telluride (CdTe) remains one of the leading thin-film absorber materials due to its near-optimal bandgap (~1.5 eV) and high absorption coefficient; however, conventional CdTe-based devices face three factors that limit their efficiency: parasitic absorption in the standard cadmium sulfide (CdS) window layer, non-radiative recombination at the interfaces, and the economically costly requirement for thick absorber layers (3 to 5 µm) given the high cost of CdTe. This work proposes a dual-interface passivation strategy that simultaneously addresses loss mechanisms at both the front and back surfaces. At the front interface, the conventional CdS buffer layer is replaced by a Cd_(1−x)Zn_(x)S alloy, whose tunable bandgap (2.4–3.7 eV) suppresses parasitic absorption in the ultraviolet and blue regions and improves band alignment with CdTe, thereby increasing the short-circuit current and open-circuit voltage. At the rear interface, a CuInTe₂ (CIT) rear surface field layer is introduced between the CdTe absorber and the molybdenum (Mo) rear contact to counteract the Schottky barrier responsible for degrading hole collection. These two modifications, when implemented together, yield efficiency gains greater than those previously reported in the literature, while also enabling a substantial reduction in the thickness of the CdTe absorber to 1 µm. Using one-dimensional drift-diffusion simulations (wxAMPS) under standard AM 1.5G illumination, this study systematically evaluates the influence of the zinc content in the Cd_(1−x)Zn_(x)S buffer layer and the thickness of the CuInTe₂ layer on the key photovoltaic performance metrics (Jsc, Voc, FF, and efficiency), with the aim of identifying the optimal device configuration for high-performance and cost-effective CdTe thin-film solar cells. Full article

In this work, scanning microwave microscopy (SMM) is used to monitor the evolution of the local microwave response, in terms of variations in the S₁₁ input reflection coefficient, in two III–V heterostructures relevant to mid-infrared photonics, namely a 150 nm thick heavily doped InGaAs layer on InP and HfO₂ (35 nm)/InGaAs (150 nm)/InP, subjected to Ga⁺ FIB milling over a broad dose range. By correlating raw, uncalibrated two-dimensional S₁₁ maps with atomic force microscopy (AFM) and Raman spectroscopy, we observe a dose-dependent evolution from implantation-dominated behavior to progressive amorphization, layer thinning and surface roughening. In the uncapped InGaAs/InP system, the SMM response varies monotonically with ion dose, consistent with progressive FIB-induced modification of the exposed InGaAs layer and, at larger milling depths, of the underlying InP substrate. In the HfO₂-capped structure, the microwave response is more complex: the oxide initially acts as a partial buffer against ion penetration, delaying damage transfer, but this effect progressively weakens as the cap is thinned and structurally degraded. The resulting S₁₁ contrast may reflect the combined effects of FIB-induced structural modifications, layer removal, local material composition, and surface morphology. Overall, the combined dataset indicates that SMM is a potentially highly sensitive probe of FIB-induced nanoscale modifications in the local microwave response, especially at low doses, provided that suitable on-chip calibration and de-embedding structures are available. Full article

Cadmium sulfide has been widely used as a conventional n-type window/buffer layer or heterojunction partner in several p-type thin-film solar cells, including CdTe/CdSeTe-, chalcopyrite-, kesterite-, antimony chalcogenide-, tin sulfide- and iron pyrite-based devices. Its success is related to its ability to form suitable heterojunctions, partially passivate absorber surfaces and provide favorable electronic selectivity. However, the parasitic absorption associated with the relatively narrow band gap of CdS, the toxicity and waste-management issues related to cadmium-containing auxiliary layers and the need for improved band alignment have motivated extensive research on CdS-free window and buffer layers. This review summarizes the main efforts devoted to replacing CdS in thin-film solar cells based on absorbers such as CdTe/CdSeTe, CIS, CIGS, CZTS, CZTSe, CZTSSe, Sb₂S₃, Sb₂Se₃, Sb₂(S,Se)₃, SnS and FeS₂. The most investigated alternative materials, including Zn(O,S), ZnS, In₂S₃, ZnMgO, ZnSnO, TiO₂, SnO₂ and SnS₂, are discussed with emphasis on their optical properties, band alignment, interface quality, deposition methods and impact on device performance. The analysis highlights that CdS replacement cannot be treated as a universal material substitution problem. Instead, each absorber and device architecture requires a specific front-interface design, where chemical compatibility, conduction band offset, defect passivation, optical transparency and process-induced interfacial modifications play a decisive role. CdS-free approaches are relatively mature for CdTe/CdSeTe- and CIGS-based solar cells, whereas kesterite absorbers, antimony chalcogenides and SnS still require further interface engineering. In FeS₂, by contrast, buffer-layer substitution remains secondary to the control of intrinsic surface and bulk electronic defects. This review provides a concise comparison of the most relevant CdS-free front/window materials and identifies key challenges for the future design of sustainable thin-film solar cells. Full article

Heteroepitaxy of single-crystalline GaN on glass represents a promising approach for low-cost, large-area optoelectronics, yet the amorphous nature of glass inherently lacks the long-range atomic order required for crystalline templating. To address this limitation, we introduce a distinctive topologically optimized pre-orienting layer (TOPL) strategy based on Cu (111) thin films, enabling the growth of an AlN (0002) buffer layer and thus achieving high-quality GaN micropyramid array epitaxy on amorphous glass. First, by introducing a disconnected Cu thin film, the grain boundaries during annealing are effectively confined within the non-epitaxial region. This process to a large extent overcomes the polycrystallization of metal templates on amorphous glass. Then, experiments demonstrated that under multiply connected configurations, the Cu (111) surface not only preserves the grain-boundary-confining property but also exhibits notable surface smoothness. Among the evaluated symmetries, the sixfold symmetry structure achieves the optimum atomic-level flatness with a root-mean-square roughness of 0.395 nm. Building upon this TOPL architecture, c-axis-oriented GaN micropyramids were grown via selective area epitaxy. The glass-based GaN micropyramid demonstrates comparable crystalline quality (threading dislocation density from a single lamella: 5.46 × 10⁸ cm⁻²) to those grown on sapphire substrates, while exhibiting reduced stress and comparable cathodoluminescence full width at half maximum. Overall, the TOPL strategy presents a promising pathway toward low-cost GaN micropyramid epitaxy on glass substrates. Full article

Colloidal processing provides a scalable non-vacuum route for fabricating CIGS and CZTSSe thin-film absorbers, but nanoparticle-derived films should be treated as constrained particulate green bodies rather than as simple chemically deposited semiconductor layers. This review reorganizes colloidal chalcogenide photovoltaics using ceramic-processing concepts: ink dispersion, green-body packing, capillary drying stress, ligand burnout, constrained shrinkage, reactive chalcogenization, transient liquid-assisted coarsening, secondary-phase control, defect chemistry, and interface reactions. The central argument is that film densification and grain growth are necessary but insufficient for high-performance CZTSSe devices. Residual carbon, Sn loss, Cu/Zn disorder, ZnSe or Cu_2−xSe secondary phases, excessive MoSe₂, and nonideal absorber/buffer band alignment can dominate open-circuit-voltage loss, fill factor, and carrier collection even when the absorber appears dense in cross-sectional microscopy. By linking ceramic-processing variables to photovoltaic loss mechanisms, this review identifies practical routes for improving colloidal chalcogenide solar cells: controlled ligand exchange and binder burnout, high-green-density precursor design, moderated chalcogen chemical potential, transient liquid management, depth-resolved phase analysis, and integrated front/back-interface engineering. Full article

Two semiflexible piezoelectric composite plate structures were developed, incorporating 1 × 9 and 2 × 9 arrays of PZT elements mounted on brass discs and mechanically secured by pop rivets within a thin plastic foil spacer positioned between two copper-clad PCB layers. This configuration provides reliable electrical contact, adequate mechanical compliance, and efficient conversion of mechanical vibration energy into electrical energy. In addition, a multifunctional thermoelectric device was realized, consisting of four cubic modules arranged around a rectangular tube and enabling both handheld operation and coupling to hot or cold surfaces. Each cube is equipped with optimized finned heat sinks and integrates four thermoelectric elements on each face. Experimental results show that each cube generates approximately 6 mW, when handheld and with icy water injected into the central tube, demonstrating its suitability as a compact and versatile thermal energy harvester. Under low-light conditions, a solar panel is supplemented by this hybrid piezoelectric–thermoelectric energy harvesting system that combines the output of a piezoelectric composite plate with the dual outputs of a thermoelectric device using an electronically isolated summing block to ensure source decoupling. Energy storage and management are implemented using a capacitor buffer for the piezoelectric device, two voltage boosters for the thermoelectric outputs, and an automatic ultra-low-power pulse width modulation buck regulator for charging supercapacitors at 5 V. Full article

Fluorocarbon (FC)/Pd/Mg multilayer thin films have attracted considerable attention as hydrogen-responsive optical materials. However, their performance is strongly limited by interfacial instability and structural degradation during deposition and hydrogen cycling. In this study, Pt/FC/Pd/Mg multilayer thin films were obtained during focused ion beam (FIB) sample preparation, and transmission electron microscopy (TEM) was employed to investigate the FC layer–mediated interfacial effects. The results reveal that Pt deposition on FC leads to the formation of a confined nanocrystalline interfacial region accompanied by a reduced apparent FC thickness and the development of a Pt–FC intermixing zone. This behavior indicates that the FC layer functions as a “soft landing” medium, dissipating kinetic energy and modifying nucleation and growth behavior. Motivated by this finding, the mechanical properties of FC films and their influence on hydrogen-cycling performance in FC/Pd/Mg/FC structures are further examined. The hardness of FC layers can be tuned from 3.03 MPa to 42.8 MPa by adjusting sputtering parameters. Hydrogen-cycling experiments reveal a strong and non-monotonic dependence on FC mechanical properties. When the FC buffer layer is relatively hard, the initial hydrogenation kinetics are improved; however, prolonged cycling leads to poor adhesion and interfacial degradation. In contrast, when the FC buffer layer is soft, hydrogenation kinetics degrade rapidly during cycling, while long-term interfacial adhesion and structural integrity are significantly improved. These results demonstrate a dual and competing role of FC layers in governing hydrogen transport and mechanical stability, highlighting a critical trade-off for the design of durable hydrogen-responsive multilayer thin films. Full article

This study systematically investigates the intrinsic vertical breakdown characteristics of 8-inch GaN-on-Si high-electron-mobility transistor (HEMT) buffer layers (extending up to the GaN channel layer) using a vertical electrode configuration. By comparing samples with different carbon doping doses, AlN insertion layers, and superlattice cycle numbers (buffer layer thickness), combined with Technology Computer-Aided Design (TCAD) simulations, the relevant mechanisms are revealed. The results show that buffer layer thickness is a critical factor determining the vertical breakdown voltage. Its increase effectively reduces the longitudinal average electric field, widens the depletion region, and increases the breakdown voltage by approximately 50%. Carbon doping compensates for carriers and suppresses leakage through deep-level acceptor traps. Inserting thin AlN layers into the superlattice has a limited effect on improving breakdown voltage. This research provides clear experimental guidance for the optimal design of high-voltage GaN HEMT buffer layers from both material and physical perspectives. Full article

Chalcopyrite-based thin-film solar cells have great potential for various applications, such as top or bottom cells in tandem devices, in addition to their use as standard single-junction modules due to their tuneable bandgap energy. A bandgap energy E_g > 1.5 eV should be targeted to realize a wide-bandgap top cell, e.g., by increasing the [Ga]/([Ga] + [In]) (GGI) ratio in Cu(In,Ga)Se₂ (CIGS) cells to the range of 0.7–1. A second approach is targeting the second theoretical efficiency maximum at a little lower E_g = 1.34 eV with a GGI around 0.6 for high-efficiency single-junction applications with reduced electrical losses. An industry-relevant (Ag,Cu)(In,Ga)Se₂ (ACIGS) co-evaporation process for wide-bandgap cells fabricated with GGI ratios above 0.6, with moderate [Ag]/([Ag] + [Cu]) (AAC) ratios < 0.1 and in-line RbF-PDT, was established on molybdenum-coated soda-lime glass substrates. Both measures, Ag alloying and RbF-PDT, can increase power conversion efficiency (PCE) mainly due to improved open-circuit voltage (V_OC). In addition, Ag addition can increase fill factor (FF)_, leading to an increase in the PCE for cells with GGI > 0.6 compared to Ag-free reference cells. (Zn,Mg)O, either with a [Mg]/([Mg] + [Zn]) ratio of 0.15 or 0.25, is a good option as high-resistive layer replacing the commonly used i-ZnO in combination with a CdS buffer. Our best ACIGS wide-bandgap solar cells with RbF-PDT and Zn_0.85Mg_0.15O (without anti-reflective coating (ARC)) from various experimental campaigns show a PCE of 12.7% (E_g = 1.50 eV), and with a slightly reduced E_g of 1.45 eV a PCE of 15.5%, with V_OC of 933 mV (V_OC deficit of 517 mV), and a good FF of 73.2%. In the case when the bandgap is significantly lowered to 1.34 eV (GGI = 0.61), to the second theoretical efficiency maximum, we achieved a PCE of 18.2% with ARC for an Ag-free CIGS cell with RbF-PDT. For this cell with a CdS/i-ZnO buffer system the V_OC deficit is 480 mV, and the FF is 78.1%. Full article

Concentrated Solar Power (CSP) tower systems require receiver materials capable of operating above 1000 °C to meet the efficiency targets of third-generation technologies (25–30%). Hybrid solutions, combining ceramic coatings with metallic substrates, offer promising thermomechanical stability under severe thermal cycling. This study investigates the high-temperature behavior of silicon carbide (SiC) coatings deposited on Fe-C-Al-Mo alloys under concentrated solar flux. Substrates were pre-oxidized to form a continuous 1–2 µm α-Al₂O₃ interlayer, serving as a chemical and mechanical buffer. SiC coatings (10–24 µm thick) were deposited via High-Temperature Chemical Vapor Deposition (HT-CVD). Characterization using XRD, SEM, EDS, and optical spectrophotometry identified cubic 3C-SiC with a globular microstructure and high compressive residual stresses (−2000 to −2400 MPa), inducing microcracking. Stress relaxation was achieved by increasing coating thickness or post-deposition annealing. Controlled oxidation formed a thin silica layer, enhancing solar absorptivity to over 90%. Accelerated thermal cycling (up to ~900 kW/m², 1050–1200 °C) revealed that coating stability depends on SiC thickness, residual stress evolution, α-Al₂O₃ interlayer thickness, and cycling severity. Optimizing these parameters is essential for ensuring the long-term durability of hybrid CSP receivers. Full article

The Northeast Black Soil Region is an important commercial grain production base in China. However, ecological issues such as black soil degradation and soil erosion pose direct threats to food security. Previous studies have mainly examined individual factors of black soil degradation. Few have integrated spatial thickness distribution with multi-dimensional ecological sensitivity. To address this gap, this study establishes an ecological sensitivity evaluation index system for Bayan County, located in the eastern Songnen High Plain. Based on a review of relevant literature, the system includes four dimensions: topography, climate, natural resources, and human activities. A combined Analytic Hierarchy Process (AHP) and Entropy Weight Method (EWM) was used to determine indicator weights. Compared with single-weighting methods, this approach balances expert judgment with data-driven variation. The results are as follows. (1) The thickness of the black soil layer in Bayan County ranges from 18 to 77 cm. Medium, thin, and thick layers account for 78.81%, 16.32%, and 4.87% of the area, respectively. The total black soil reserve is estimated at about 1.267 billion m³. (2) Among the primary indicators, natural resources have the highest weight (0.53). The five most important secondary indicators are the river buffer zone (0.14), NDVI (0.13), soil type (0.12), land use type (0.12), and road buffer zone (0.09). (3) The overall ecological sensitivity of the county is moderate, with a composite index ranging from 1.45 to 4.45. The proportions of extremely sensitive, highly sensitive, moderately sensitive, mildly sensitive, and insensitive areas are 10.79%, 25.51%, 28.95%, 24.23%, and 10.52%, respectively. These findings provide a scientific basis for ecological protection and black soil conservation. They also support the development of targeted, zone-specific management strategies in Bayan County. Full article

Cd-doped ZnS thin films (0–6 at.%) were deposited by SILAR and assessed as buffer layers for thin-film solar cells. XRD shows a single zinc-blende phase, with a small lattice expansion after Cd incorporation. As the Cd content increases, transmittance decreases and the direct band gap narrows, pushing absorption further into the visible. DFT with mBJ reproduces this redshift and attributes it to Cd-related states near the band edges. Hall measurements indicate stronger n-type transport at higher Cd levels, with lower resistivity, higher mobility, and a larger electron concentration. Overall, about 6% Cd provides a workable balance between transparency, absorption, and conductivity, making ZnS:Cd a suitable buffer-layer candidate. Full article

The substantially lower breakdown electric field of Si compared to GaN necessitates thick buffer layers in Si-based GaN power devices for medium-voltage applications, significantly increasing cost. Recently, sapphire substrates, offering high electrical insulation and excellent mechanical strength, have emerged as a promising alternative. In this work, we demonstrate a CMOS-compatible process for sapphire-based GaN MIS-HEMTs utilizing a thin buffer layer. The fabricated devices with a W_G of 20.4 mm and an L_GD of 24 μm achieve a high off-state breakdown voltage >1650 V and a maximum on-state current > 4.1 A, with tight statistical distributions of V_TH and R_ON across the wafer. Furthermore, statistical characterization results of dynamic R_ON and leakage current under electrical stress conditions at both room temperature and 150 °C, confirm operational viability at high temperatures. Finally, long-term reliability for 650 V operation is validated by high-temperature reverse bias (HTRB) accelerated aging tests. Full article

The safe disposal of high-level radioactive waste (HLW) is a significant challenge in the nuclear industry. As the buffer backfill material for deep geological disposal engineering barriers, the shrinkage characteristics of bentonite–sand mixtures are critical to the long-term stability of repositories. This study systematically conducted drying shrinkage tests using an improved thin-film technique under varying sand contents R_s (0–50%), salt solution concentrations (0–1.5 mol/L), and ion types (Na⁺, Mg²⁺, Ca²⁺, Cl⁻, SO₄²⁻). The mechanisms of the effects of sand content and salt solutions on the shrinkage behavior of bentonite were revealed based on the results. In addition, the rationality of the MCG-B model in simulating the shrinkage characteristics of mixtures was also discussed. The results show that a sand content of 30% is the minimum sand content for inhibiting the shrinkage behavior of bentonite–sand mixtures observed in this work: below this ratio, bentonite dominates the shrinkage process, and samples are prone to cracking due to uneven matrix suction; above this ratio, quartz sand forms a rigid skeleton that significantly inhibits volume shrinkage and accelerates water evaporation. Salt solutions suppress shrinkage by compressing the thickness of the diffuse double layer and inducing ion crystallization. Higher cation concentrations and valences (Mg²⁺ > Na⁺ > Ca²⁺) enhance the inhibitory effect. Crystalline salts such as Na₂SO₄ cause measurement deviations in water content due to hydration and delay the shrinkage process. However, NaCl solutions effectively inhibit shrinkage with minimal impact on shrinkage time. Fitting results with the MCG-B model (Coefficient of determination > 0.97) demonstrate that the MCG-B model can empirically describe the results of thin-film technique experiment, though the model’s prediction accuracy decreases for the residual shrinkage stage at high sand contents (>40%). This study provides a theoretical basis for optimizing buffer material proportions and curing processes, with significant implications for the long-term safety of HLW repositories. Full article