Briefings Venkatesh, B.; Thériault, R.; St-Laurent, F. ...
American scientist,
03/2014, Letnik:
102, Številka:
2
Journal Article
According to this theory, oxygen atoms bound up in minerals are sometimes short an electron. For 45 years. solar physicists suspected that the Sun also experienced another type of convection called ...giant cells, similar to but even larger and slower than the supergranules, but such cells had never been substantiated. Since 2010, NASA's orbiting Solar Dynamics Observatory has been imaging the Sun continuously, providing the data needed to track the motion of supergranules and detect the giant convective cells, which span some 200,000 kilometers and move at about 29 kilometers per hour.
Arsenic (As) has been shown to be an effective p-type dopant for CdTe, although high performance in As-doped devices remains difficult to achieve. Arsenic is prone to self-compensation in CdTe, as ...evidenced by the accumulation of dopant atoms in CdTe/Cd(Se,Te) near the interface with MgxZn1-xO (MZO). In this study, we use SCAPS 1D modeling software to investigate the effect of near-interface compensation, helping elucidate loss pathways in present-day As-doped devices and informing future growth directions. We consider three possible results of As accumulation: shallow donors, deep recombination centers, and a thin layer of excess acceptor accumulation. The reduction in near-interface carrier concentration caused by shallow donors is shown to improve open-circuit voltages (Voc), whereas deep levels are detrimental to all performance parameters. The thin charge layer affects capacitance-voltage (CV) measurements by reducing the depletion width while maintaining the same carrier concentration, replicating CV behavior that has been observed in actual devices. These results illustrate the importance of monitoring dopant accumulation within 100 nm of the interface, and suggest that reducing or eliminating the As concentration in this region would be beneficial. An undoped Cd(Se,Te) layer at the interface is suggested as a possible device structure to boost performance.
•Compensating donors can significantly reduce CdTe solar cell performance.•Significant effects are seen even when donors are concentrated near the interface.•Modeled charge buildup at interface narrows depletion widths as seen in devices.•Low-doped or undoped region near the interface can improve performance.
CdTe-based solar cells exhibiting 19% power conversion efficiency were produced using widely available thermal evaporation deposition of the absorber layers on SnO2-coated glass with or without a ...transparent MgZnO buffer layer. Evaporating CdSe and CdTe sequentially by thermal evaporation and subsequent CdCl2 annealing establishes efffective CdSeTe band grading as well as dense, large-grain films. These results show that high-performance II–VI photovoltaics can be made by inexpensive, commercially available evaporation systems without the need to build customized equipment, enabling CdTe photovoltaics research and manufacturing to be more accessible to the broader photovoltaics community.
Abstract Background Pathogenic Leptospira species are globally important zoonotic pathogens capable of infecting a wide range of host species. In marine mammals, reports of Leptospira have ...predominantly been in pinnipeds, with isolated reports of infections in cetaceans. Case presentation On 28 June 2021, a 150.5 cm long female, short-beaked common dolphin ( Delphinus delphis delphis ) stranded alive on the coast of southern California and subsequently died. Gross necropsy revealed multifocal cortical pallor within the reniculi of the kidney, and lymphoplasmacytic tubulointerstitial nephritis was observed histologically. Immunohistochemistry confirmed Leptospira infection, and PCR followed by lfb1 gene amplicon sequencing suggested that the infecting organism was L. kirschneri. Leptospira DNA capture and enrichment allowed for whole-genome sequencing to be conducted. Phylogenetic analyses confirmed the causative agent was a previously undescribed, divergent lineage of L. kirschneri . Conclusions We report the first detection of pathogenic Leptospira in a short-beaked common dolphin, and the first detection in any cetacean in the northeastern Pacific Ocean. Renal lesions were consistent with leptospirosis in other host species, including marine mammals, and were the most significant lesions detected overall, suggesting leptospirosis as the likely cause of death. We identified the cause of the infection as L. kirschneri , a species detected only once before in a marine mammal – a northern elephant seal ( Mirounga angustirostris ) of the northeastern Pacific. These findings raise questions about the mechanism of transmission, given the obligate marine lifestyle of cetaceans (in contrast to pinnipeds, which spend time on land) and the commonly accepted view that Leptospira are quickly killed by salt water. They also raise important questions regarding the source of infection, and whether it arose from transmission among marine mammals or from terrestrial-to-marine spillover. Moving forward, surveillance and sampling must be expanded to better understand the extent to which Leptospira infections occur in the marine ecosystem and possible epidemiological linkages between and among marine and terrestrial host species. Generating Leptospira genomes from different host species will yield crucial information about possible transmission links, and our study highlights the power of new techniques such as DNA enrichment to illuminate the complex ecology of this important zoonotic pathogen.
Here, we report on nm-scale electrical potential imaging throughout As-doped and Cu-doped CdSeTe absorbers using Kelvin probe force microscopy (KPFM). The potential imaging was conducted both ...laterally and vertically on beveled films using ion milling at small glancing angle. KPFM images electrical potential on the beveled surface and assesses defect charging in the subsurface region within a screening length from the beveled surface. We found that the grain boundaries were positively charged and that there were significant potential fluctuations in both grain boundary versus grain interior and intragrain. We further found that these potential fluctuations decreased significantly toward the front interface. Time of flight secondary ion mass spectrometry imaging shows that Se content increased toward the front interface, consistent with Se passivation of defects. The potential fluctuation was induced by defect charging, and the results elucidate different details of the defect configurations and grain structures of the films with different CdCl2 treatment temperatures in the As-doped CdSeTe. The defect configurations in the region near the front interface can be a main factor contributing to the device performance difference. Our potential imaging provides insights about the defects throughout the absorber films, and shows that the potential fluctuation has a direct correlation to the Voc deficit.
We report on nm-scale electrical potential imaging throughout As-doped and Cu-doped CdSeTe absorbers using Kelvin probe force microscopy (KPFM). The potential imaging was conducted both laterally and ...vertically on beveled films using ion milling at small glancing angle. KPFM images electrical potential on the beveled surface and assesses defect charging in the subsurface region within a screening length from the beveled surface. We found that the grain boundaries were positively charged and that there were significant potential fluctuations in both grain boundary versus grain interior and intragrain. We further found that these potential fluctuations decreased significantly toward the front interface. Time of flight secondary ion mass spectrometry imaging shows that Se content increased toward the front interface, consistent with Se passivation of defects. The potential fluctuation was induced by defect charging, and the results elucidate different details of the defect configurations and grain structures of the films with different CdCl2 treatment temperatures in the As-doped CdSeTe. The defect configurations in the region near the front interface can be a main factor contributing to the device performance difference. Our potential imaging provides insights about the defects throughout the absorber films, and shows that the potential fluctuation has a direct correlation to the Voc deficit.
•Achieved nm-scale electrical potential mapping throughout the CdSeTe absorber both laterally and vertically.•Found that electrical potential fluctuation decreases significantly with approaching the front interface.•Found that the decrease in electrical potential fluctuation results from Se passivation.•Found that detailed defect configuration within the depletion width can cause significant difference in device performance.•The real-space electrical potential is a reflection of defects, and also a direct contributor to the device voltage deficit.
Mg x Zn 1- x O (MZO) shows great promise to replace CdS as a buffer layer in CdTe-based solar cells. It is more transparent, and the MZO bandgap and electron density can be tuned, thus providing ...flexibility in controlling the conduction band offsets and recombination rates between transparent conductive oxide/MZO and MZO/CdSeTe interfaces. Integrating this material into solar cell devices has been frustrated by the common observation of abnormal current-voltage curves. Simulations indicate that this anomalous behavior can be attributed to front interface barrier effects. Experiments demonstrate that this common MZO interface problem can be resolved experimentally by surface preparation, preheat steps, and removing oxygen during absorber deposition and CdCl 2 treatment. Oxygen during the cell fabrication process is likely to alter MZO properties and MZO/CdSeTe band alignment. After addressing these interface issues and modest optimization, devices with high short-circuit density of 29 mA/cm 2 and efficiency above 16% are demonstrated.
CdTe defect chemistry is adjusted by annealing samples with excess Cd or Te vapor with and without extrinsic dopants. We observe that Group I (Cu and Na) elements can increase hole density above 1016 ...cm−3, but compromise lifetime and stability. By post-deposition incorporation of a Group V dopant (P) in a Cd-rich ambient, lifetimes of 30 ns with 1016 cm−3 hole density are achieved in single-crystal and polycrystalline CdTe without CdCl2 or Cu. Furthermore, phosphorus doping appears to be thermally stable. This combination of long lifetime, high carrier concentration, and improved stability can help overcome historic barriers for CdTe solar cell development.
Polycrystalline photovoltaic materials offer low costs and good scalability; however, grain boundaries in these materials are extended defects, which can drastically increase carrier recombination. ...Interestingly, three leading polycrystalline thin-film technologies—cadmium telluride (CdTe), CuIn1-xGaxSe2 (CIGS), and perovskite solar cells (PSCs)—passivate absorber surfaces in the same way: via formation of low-dimensional, typically two-dimensional (2D), van der Waals materials. This has primarily occurred serendipitously through process optimization, but in some cases, 2D capping layers are intentionally incorporated to improve device performance. Here, evidence compiled from the literature, supplemented with new data where necessary, is presented to illustrate the existence of 3D/2D interfaces in CdTe, CIGS, and PSCs, and their correlation with improved passivation and device performance. This suggests that 3D/2D passivation might be a heretofore unappreciated key to successful polycrystalline thin-film photovoltaics. Finally, the desired attributes of successful low-dimensional layers are presented with rational design strategies for next-generation polycrystalline solar cells.
Leading polycrystalline thin-film technologies—cadmium telluride (CdTe), CuIn1-xGaxSe2 (CIGS), and perovskite solar cells (PSCs)—are based on very different materials, defect chemistries, and device processing conditions, yet all achieve efficiencies rivaling that of crystalline silicon. We argue that a previously unappreciated key to their shared success is passivated (i.e., benign) surfaces via formation of two-dimensional (2D) van der Waals materials. In CdTe, the 2D material is CdCl2; in CIGS, it is XInSe2 (X = K, Rb, Cs) with X depending on the heavy-alkali post-deposition treatment; and in lead halide PSCs, PbI2 forms naturally, but many new, more stable, 2D materials have recently been incorporated. Importantly, this work shows that the large body of knowledge developed in PSCs on 3D/2D interface formation can, and should, be leveraged by other polycrystalline technologies. In many cases, the formation of 2D materials has been a consequence of empirical process optimization rather than by design. Here, we advocate for the active exploitation of 2D materials and their highly tunable properties both to further enhance the performance of leading technologies and as a strategy to elevate other polycrystalline technologies that have underperformed to date (e.g., GaAs). An important example of the tremendous benefit that can be gained by exploiting 2D material properties is the greatly enhanced device stability of 3D/2D PSCs. By outlining key attributes of successful 3D/2D systems along with rational design strategies for implementation, we invite researchers of diverse backgrounds—not just photovoltaics but functionalized materials more generally—to consider how the advanced field of 2D materials can be leveraged in their unique system. Moreover, this work presents an opportunity for 2D-material researchers to overcome some of their major challenges, such as commercialization, by leveraging the expertise of the photovoltaic industry.
Polycrystalline thin-film solar cells provide the lowest-cost pathway for scalable photovoltaic technologies. However, their many interfaces (i.e., grain boundaries) can drastically increase electron-hole recombination if not passivated (made benign). Here, we show that three of the highest-performing thin-film technologies—cadmium telluride (CdTe), CuIn1-xGaxSe2 (CIGS), and perovskites—all have naturally passivated surfaces via formation of two-dimensional capping layers. Key design strategies are proposed such that this passivation scheme can be employed in polycrystalline functionalized materials more generally.
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