Detrimental Defects Research Articles

Designing Atomic Interface in Sb2S3/CdS Heterojunction for Efficient Solar Water Splitting.

In the emerging Sb2S3-based solar energy conversion devices, a CdS buffer layer prepared by chemical bath deposition is commonly used to improve the separation of photogenerated electron-hole pairs. However, the cation diffusion at the Sb2S3/CdS interface induces detrimental defects but is often overlooked. Designing a stable interface in the Sb2S3/CdS heterojunction is essential to achieve high solar energy conversion efficiency. As a proof of concept, this study reports that the modification of the Sb2S3/CdS heterojunction with an ultrathin Al2O3 interlayer effectively suppresses the interfacial defects by preventing the diffusion of Cd2+ cations into the Sb2S3 layer. As a result, a water-splitting photocathode based on Ag:Sb2S3/Al2O3/CdS heterojunction achieves a significantly improved half-cell solar-to-hydrogen efficiency of 2.78% in a neutral electrolyte, as compared to 1.66% for the control Ag:Sb2S3/CdS device. This work demonstrates the importance of designing atomic interfaces and may provide a guideline for the fabrication of high-performance stibnite-type semiconductor-based solar energy conversion devices.

Achieving high open-circuit voltage in efficient kesterite solar cells via lanthanide europium ion induced carrier lifetime enhancement

Short carrier lifetimes is a key challenge limiting the open-circuit voltage (VOC) and power conversion efficiency (PCE) of kesterite Cu2ZnSn(S,Se)4 (CZTSSe) solar cells. In this work, for the first time, lanthanide europium (Eu) ions have been introduced into Ag-incorporated CZTSSe absorber layer, which can modify the selenization reaction pathway during the initial selenization process, leading to high-quality (Ag, Eu)-CZTSSe absorber with large compact crystal grains and benign surface potential fluctuations. This innovative absorber engineering can also optimize defects dynamics with less detrimental defects and defects-assisted non-radiative recombination. Thus, significantly enhanced minority carrier lifetimes from 0.97 to 3.15 ns can be achieved, representing one of the top values among various bulk and/or interface engineering treated CZTSSe. The champion CZTSSe thin-film solar cell exhibits an impressive VOC of 545.6 mV, accompanied with a stimulating increase in PCE from 10.68% to 13.30%. These findings underscore the potential of lanthanide cation doping to drive significant advancements in CZTSSe photovoltaic technology, and therefore promoting its further development and future applications.

Sulfur‐Supplemented Vapor Transport Deposition of Sb2S3 and Sb2(S,Se)3 for High‐Performance Hydrogen Evolution Photocathodes

Chalcogen vacancy has long been recognized as a detrimental deep‐level defect that can induce severe charge recombination and diminish the quasi‐Fermi‐level splitting in Sb2S3 and Sb2Se3, especially when they are prepared by physical vapor deposition in vacuum. In order to counter this limitation, a sulfur‐supplemented vapor transport deposition technique is proposed, which intentionally introduces low pressure sulfur vapor and can thus afford low‐defect‐density antimony chalcogenide films. The resultant photocathodes modified with conformal TiO2 protection layer and Pt cocatalyst demonstrate a photocurrent as high as 20 mA cm−2 along with a much improved fill factor and onset potential, achieving an applied bias photoconversion efficiency above 1%. This work highlights the importance of the vacancy defect passivation and the preferential crystalline orientation in the film in promoting the photocathode performance.

Agglomerating behavior of in-situ TiB2 particles and strength-ductility synergetic improvement of in-situ TiB2p/7075Al composites through ultrasound vibration

Agglomerates of in-situ particles are the key detrimental defects in particulate reinforced aluminum matrix composites (PRAMCs) by acting as Achilles' heel leading to the premature failure of the materials. Effective methods to disperse/eliminate these agglomerates rely on in-depth understanding of the agglomeration mechanism of the in-situ particles. In this work, the agglomerating behavior of TiB2 particles in Al-Ti-B system was investigated through the thermit reactions between mixed fluorides and molten aluminum. The results indicate that the morphological patterns of TiB2 agglomerates are inherited from the preformed Al3Ti intermedium. The formation of flocculent, shell and flaky TiB2 agglomerates are the results of the diffusing boron atoms continuously reacting with Al3Ti. The in-situ Al-TiB2 was used as a precursor to prepare TiB2p/7075 Al composites. In particular, ultrasound vibration treatment was applied to explore if a locally forced oscillation can deagglomerate the TiB2 agglomerates. Microstructural observations strongly support such speculation. Thanks to the deagglomeration and dispersion of TiB2 particles, both the strength and ductility of the PRAMC have been improved drastically. The fracture surface of the composites was transformed from particle debonding to the dominance of ductile fracture.

A Multifunctional Amino Acid Enables Direct Recycling of Spent LiFePO4 Cathode Material.

Lithium iron phosphate (LiFePO4 , LFP) batteries are extensively used in electric vehicles and energy storage due to their good cycling stability and safety. However, the finite service life of lithium-ion batteries leads to significant amounts of retired LFP batteries, urgently required to be recycled by environmentally friendly and effective methods. Here, a direct regeneration strategy using natural and low-cost L-threonine as a multifunctional reductant is proposed. The hydroxyl groups and amino groups in L-threonine act as electron donors and nitrogen sources, respectively. The reductive environment created by L-threonine not only aids in converting the degraded FePO4 phase back to a single LFP phase but also facilitates the elimination of detrimental Li-Fe anti-site defects; thus, reconstructing fast Li+ diffusion channels. Meanwhile, N atoms derived from amino groups are able to dope into carbon layers, generating more active sites and enhancing the conductive properties of LFP particles. The regenerated LFP shows great electrochemical performance with a discharge capacity of 147.9 mAh g-1 at 1 C and a capacity retention of 86% after 500 cycles at 5 C. Further, this approach is also feasible for LFP black mass sourced from practical industrial dismantling lines, providing considerable prospects for the large-scale recycling of LFP batteries.

Cs-treatments in Kesterite Thin-Film Solar Cells for Efficient Perovskite Tandems.

Cu2ZnSn(S,Se)4 (CZTSSe) thin film solar cells are an attractive choice for a bottom cell of the low-cost and environmental tandem solar cells with perovskite. However, the progress in developing efficient perovskite/CZTSSe tandem solar cells has been hindered by the lack of high performance of the CZTSSe bottom cell. Here, an efficient CZTSSe bottom cell is demonstrated by adopting a facile and effective CsF treatment process. It is found that the CsF treatment not only facilitates grain growth and improves phase homogeneity by suppressing the detrimental deep-level defects and secondary phases, but also induces larger band bending and stronger drift force at the P-N junction. As a result, the carrier extraction/transport can be effectively accelerated, while reducing the interfacial recombination. These combined effects eventually result in a significant performance enhancement from 8.38% to 10.20%. The CsF-treated CZTSSe solar cell is finally applied to the mechanically-stacked perovskite/CZTSSe 4-terminal tandem cell by coupling a semi-transparent perovskite top cell, which exhibits the highest reported tandem efficiency of 23.01%.

Single Photon Emitters in Hexagonal Boron Nitride Fabricated by Focused Helium Ion Beam

AbstractThe 2D layered hexagonal boron nitride (hBN) material is a promising platform for making single photon emitters (SPEs). Integrate SPEs with photonic cavities or waveguides, requires the deterministic positioning of these emitters as accurately as possible. Among all of the alternative techniques, He+ focused ion beam (FIB) theoretically has sub‐nanometer precision, but its practical positioning accuracy in processing SPEs is limited by the inevitable detrimental byproduct defects. So far, it remains challenging to achieve an accuracy below 100 nm for the positioning of SPEs in hBN. Here, we present a two‐step method for creating SPEs at the predetermined positions in hBN that combines the He+ FIB irradiation and thermal annealing under an oxygen atmosphere. With this method, we have realized the positioning accuracy of less than 50 nm, which, to the best of our knowledge, stands as the highest among the currently available hBN SPEs preparation methods. Moreover, the SPE conversion yield was over 35% and the emission brightness of individual SPE achieved up to 3 × 105 counts/s at room temperature. These SPEs fabricated precisely with nanoscale accuracy in hBN are expected to be good candidates for making large‐scale integrated SPEs in photonic circuits.

In‐gap States and Carrier Recombination in Quasi‐2D Perovskite Films

In‐gap states and their effect on recombination rates in quasi‐2D lead–iodide‐based perovskites, intercalated with various spacer molecules, are studied using a combination of scanning tunneling spectroscopy and temperature‐dependent photoconductivity measurements. The results are further analyzed by a Shockley–Read–Hall model. Indications for shallow in‐gap states, positioned at about 0.15–0.2 eV below the bottom of the conduction band, are found. These states are identified as dominating the recombination route of photogenerated carriers in these systems, with a relatively large capture coefficient of about 10−5–10−6 cm3 s−1 at room temperature. First‐principles calculations based on density functional theory imply that these states are not an intrinsic effect of the inclusion of the spacer molecules, but rather one that arises from chemical defect formation or structural deformation of the perovskite layers. The results suggest that further improvement of the performance of solar cells that are based on quasi‐2D perovskites requires, along with enhancing carrier mobility, efforts to suppress the concentration of these detrimental defect states.

Thermal diffused post-selenization for enhancing the photovoltaic performance of thermally evaporated Sb2Se3 solar cell

Sb2Se3 is a promising absorber material for photovoltaic applications owing to its suitable bandgap and high absorption coefficient. However, the initial deposition of the precursor Sb2Se3 thin films using thermal evaporation with an annealing process, results in poor crystallinity and inadequate Se content, leading to significantly low device efficiency and some deep-level detrimental defects. To address these issues, herein, we propose a facile thermal diffusion post-selenization method to supplement Se into post-deposited Sb2Se3 thin films. This process not only achieves stoichiometric composition but also improves the crystallinity of the samples, thereby reducing defect density and carrier recombination. As a result, the efficiency of the fabricated Mo/Sb2Se3/CdS/ITO/Ag solar cell is significantly enhanced from 0.66% to 3.29%.

12.84% Efficiency Flexible Kesterite Solar Cells by Heterojunction Interface Regulation

AbstractDue to their environmental friendliness, low cost, and versatility in applications, flexible Cu2ZnSn(S, Se)4 (CZTSSe) solar cells have garnered significant attention in recent years. However, the lack of alkali metal elements in the flexible substrate has posed a challenge to the advancement of flexible CZTSSe solar cells. In this study, a post‐treatment strategy is proposed involving Rb ions to simultaneously regulate the surface properties of the CZTSSe film and the reactions during the CdS chemical bath deposition (CBD) process. Material and chemical characterization results confirm that Rb ions effectively passivate the detrimental Se0 defect, leading to a more active surface for the CdS epitaxial growth. Additionally, the coordination between Rb ions and thiourea in the CBD solution improves the ion‐by‐ion deposition of the CdS layer. These beneficial effects significantly improve the heterojunction interface and consequently enable the flexible CZTSSe solar cell to achieve a record total‐area efficiency of 12.84% and excellent bending performance. Overall, the heterojunction interface regulation strategy employed in this work, along with the obtained remarkable results, offer promising prospects for the development of flexible CZTSSe solar cells.

Carbon control and densification of WC-8%Co fabricated by extrusion-based additive manufacturing under pressureless sintering

In this study, WC-8%Co cemented carbide was fabricated using feedstock with paraffin/polymer binder via extrusion-based additive manufacturing method and post processing. After extracting paraffin by solvent immersion, the atmosphere in furnace for thermal debinding and sintering processing were adjusted to control the carbon content of the final sintered body. The results showed that thermal debinding under industrial hydrogen atmosphere results in the formation of decarbonized phase in the sintered body. Thermal debinding under vacuum and argon atmosphere leads to formation of uncombined carbon. Sintered under hydrogen and vacuum can effectively promote the further decomposition and transformation of residual carbon, while sintered under argon atmosphere leads to aggregation of uncombined carbon. Decarbonized phases have negative impact on the strength of cemented carbides, and excessive uncombined carbon is also detrimental defects that decrease in the strength and hardness of cemented carbides. The shrinking and densification of brown body can be accomplished when sintered at 1340 ℃, the pores were almost completely eliminated and size of print defect reduced. Sintered body show superior mechanical properties. An exorbitant high sintering temperature lead to the growth of WC grains, while excessive grain growth can worsen mechanical properties of the sintered body.

3D CNN and grad-CAM based visualization for predicting generation of dislocation clusters in multicrystalline silicon

We propose a machine learning-based technique to address the crystallographic characteristics responsible for the generation of crystal defects. A convolutional neural network was trained with pairs of optical images that display the characteristics of the crystal and photoluminescence images that show the distributions of crystal defects. The model was trained to predict the existence of crystal defects at the center pixel of the given image from its optical features. Prediction accuracy and separability were enhanced by feeding three-dimensional data and data augmentation. The prediction was successful with a high area under the curve of over 0.9 in a receiver operating characteristic curve. Likelihood maps showing the distributions of the predicted defects are in good resemblance with the correct distributions. Using the trained model, we visualized the most important regions to the predicted class by gradient-based class activation mapping. The extracted regions were found to contain mostly particular grains where the grain boundaries changed greatly due to crystal growth and clusters of small grains. This technique is beneficial in providing a rapid and statistical analysis of various crystal characteristics because the features of optical images are often complex and difficult to interpret. The interpretations can help us understand the physics of crystal growth and the effects of crystallographic characteristics on the generation of detrimental defects. We believe that this technique will contribute to the development of a better fabrication process for high-performance multicrystalline materials.

Fabrication of perovskite solar cells with PCE of 21.84% in open air by bottom-up defect passivation and stress releasement

The archetypical n-type semiconductor material, tin oxide (SnO2), is common and well-known electron transport layer (ETL) material in regular perovskite solar cells (PSCs) due to the superior electron mobility and suitable energy level alignment with perovskite. However, plentiful detrimental defects concentrated at perovskite/SnO2 ETLs interface and unfavorable residual stress within perovskite films, compromise and dampen the photovoltaic performance and shelf stability of PSCs. Herein, alkali metal salts (i.e., 2, 2′-biquinoline-4, 4′-dicarboxylic acid alkali metal salts (BCA-2H, BCA-2Na, and BCA-2K)) are employed as pre-buried modifiers in SnO2 films to achieve a holistic amelioration of ETLs, perovskite photoactive layer, and their interface heterojunction. The BCA modification facilitates crystal orientation and crystalline of SnO2 nanocrystals, instrumental in decreasing trap state densities within functional layers, releasing interfacial residual tensile strain, and upgrading perovskite film performance. In comparison to BCA-2H- and BCA-2Na-doped ETLs, the BCA-2K decoration corroborate better defect passivation and stress release effect originating from preferable interface enhancement and desirable surface chemical properties. Consequently, the PSCs based on SnO2-BCA-2K ETL fabricated under open-air conditions deliver the champion efficiency of 21.84% accompanied by negligible hysteresis. Moreover, the unpacked devices maintain 81.2% of its original value after 1200 h storage under an ambient condition of 55 ± 5% (relative humidity, RH) and 25 ± 5 ℃ with open-circuit conditions.

Inferior fatigue resistance of additively-manufactured Ni-based superalloy 718 and its dominating factor

Push-pull and torsional fatigue tests were conducted using additively-manufactured, Ni-based superalloy 718 samples with various defects and different microstructures, aiming to comprehensively examine fatigue limit determining factors such as detrimental defects and microstructural features. Test results revealed that the fatigue limit in each loading condition was governed by a shear-mode, crack-growth threshold, exhibiting a crack-size dependence similar to that of the wrought alloy. The additively-manufactured materials displayed a substantially reduced crack threshold as compared to wrought ones, potentially attributed to a high volume of low twist angles between neighboring crack-planes.

4-biphenylcarboxylic acid as defect passivation for high-efficient perovskite solar cells

Metal halide perovskite solar cells (PSCs) have been considered as one of the most promising candidates for clean and renewable energy sources, but the existence of the detrimental defects at the surface and grain boundaries seriously deteriorates the power conversion efficiency (PCE) and stability of PSCs. Defect passivation has been verified to efficiently enhance the PCE and stability of PSCs. Herein, a kind of 4-biphenylcarboxylic acid (4-BBC) is first utilized to passivate the perovskite film by a post-treatment strategy, finally improving the performance of PSCs. The carbonyl group of 4-BBC as Lewis base can interact with the uncoordinated Pb2+ ions to heal the I- vacancy defects, and its hydroxyl group can form hydrogen bond with I- anion of the perovskite to suppress the I- ionic migration. The hydrophobic biphenyl group of 4-BBC can also be beneficial to improve the stability of the perovskite film. As a result, the inverted PSCs with 4-BBC passivation indicate a best PCE (20.32 %) with lower hysteresis index (HI) of 0.39 % and better stability in comparison with the control PSCs (PCE = 18.71 %). The synergistic passivation of 4-BBC developed in this work offers an effective strategy for the fabrication of highly efficient and stable PSCs.

CRISPR-Cas9 in hiPSCs: A new era in personalized treatment for Stargardt disease

CRISPR-Cas9 in hiPSCs: A new era in personalized treatment for Stargardt disease

Secondary defects of as-grown oxygen precipitates in nitrogen doped Czochralski single crystal silicon

In this work, as-grown defects and their secondary defects in 300 mm nitrogen-doped Czochralski-grown single-crystal silicon (NCZ-Si) are investigated. Secondary defects are revealed by homogeneous epitaxial layer growth, and as-grown defects are decorated via gaseous hydrogen chloride (HCl) etching. Localized light scattering (LLS) technique is utilized to inspect defect distribution and provide the latex sphere equivalent (LSE) size to differentiate defect types. With the locations of LLS, the morphology of defect is observed by scanning electron microscopy (SEM). According to the results, it indicated that secondary defects are extrinsic dislocation loops and stacking fault (SF) loops, which are induced by as-grown oxygen precipitates during the growth and cooling process. Furthermore, the correlation between the counts of secondary defects and nitrogen concentration is obtained. It contributes to the optimization of nitrogen doping to avoid the generation of detrimental defects for device operation.

In-situ crack and keyhole pore detection in laser directed energy deposition through acoustic signal and deep learning

Cracks and keyhole pores are detrimental defects in alloys produced by laser directed energy deposition (LDED). Laser-material interaction sound may hold information about underlying complex physical events such as crack propagation and pores formation. However, due to the noisy environment and intricate signal content, acoustic-based monitoring in LDED has received little attention. This paper proposes a novel acoustic-based in-situ defect detection strategy in LDED. The key contribution of this study is to develop an in-situ acoustic signal denoising, feature extraction, and sound classification pipeline that incorporates convolutional neural networks (CNN) for online defect prediction. Microscope images are used to identify locations of the cracks and keyhole pores within a part. The defect locations are spatiotemporally registered with acoustic signal. Various acoustic features corresponding to defect-free regions, cracks, and keyhole pores are extracted and analysed in time-domain, frequency-domain, and time-frequency representations. The CNN model is trained to predict defect occurrences using the Mel-Frequency Cepstral Coefficients (MFCCs) of the lasermaterial interaction sound. The CNN model is compared to various classic machine learning models trained on the denoised acoustic dataset and raw acoustic dataset. The validation results shows that the CNN model trained on the denoised dataset outperforms others with the highest overall accuracy (89%), keyhole pore prediction accuracy (93%), and AUC-ROC score (98%). Furthermore, the trained CNN model can be deployed into an in-house developed software platform for online quality monitoring. The proposed strategy is the first study to use acoustic signals with deep learning for insitu defect detection in LDED process.

Tracking the evolution of hot tears in aluminium alloys using high-speed X-ray imaging

Hot tears are detrimental defects forming during the final stage of solidification when the remaining liquid loses the capacity to compensate for liquid to solid volume shrinkage. Although a mature semi-quantitative description of hot tearing has been developed, little is known about the dynamic evolution of hot tears as experimental studies have been conducted mostly post-solidification or in semi-static in-situ conditions. Here, we present a methodology to investigate the evolution of hot tears with high spatial and temporal resolution using synchrotron-based X-ray radiography. We develop a novel hot tear detection and tracking algorithm for quantification of hot tear density, area fraction and merging from the analysis of radiographic sequences of the solidification of thin metal samples. The methodology is demonstrated for an Al-5wt%Cu alloy and examples of the results and new insights that can be achieved are described.

Longitudinal Evaluation Using Preclinical 7T-Magnetic Resonance Imaging/Spectroscopy on Prenatally Dose-Dependent Alcohol-Exposed Rats.

Prenatal alcohol exposure causes many detrimental alcohol-induced defects in children, collectively known as fetal alcohol spectrum disorders (FASD). This study aimed to evaluate a rat model of FASD, in which alcohol was administered at progressively increasing doses during late pregnancy, using preclinical magnetic resonance (MR) imaging (MRI) and MR spectroscopy (MRS). Wistar rats were orally administered 2.5 mL/day of ethanol (25% concentration) on gestational day 15, and postnatal fetuses were used as FASD models. Four groups were used: a control group (non-treatment group) and three groups of FASD model rats that received one, two, or four doses of ethanol, respectively, during the embryonic period. Body weight was measured every other week until eight weeks of age. MRI and MRS were performed at 4 and 8 weeks of age. The volume of each brain region was measured using acquired T2-weighted images. At 4 weeks of age, body weight and cortex volume were significantly lower in the three FASD model groups (2.5 × 1: 304 ± 6 mm3, p < 0.05; 2.5 × 2: 302 ± 8 mm3, p < 0.01; 2.5 × 4: 305 ± 6 mm3, p < 0.05) than they were in the non-treatment group (non-treatment: 313 ± 6 mm3). The FASD model group that received four doses of alcohol (2.5 × 4: 0.72 ± 0.09, p < 0.05) had lower Taurine/Cr values than the non-treatment group did (non-treatment: 0.91 ± 0.15), an effect that continued at 8 weeks of age (non-treatment: 0.63 ± 0.09; 2.5 × 4: 0.52 ± 0.09, p < 0.05). This study is the first to assess brain metabolites and volume over time using MRI and MRS. Decreases in brain volume and taurine levels were observed at 4 and 8 weeks of age, suggesting that the effects of alcohol persisted beyond adulthood.