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Search indexed NASA NTRS and DOE OSTI research on propulsion, heat transfer, battery materials and energy systems. Follow report and document links to the original sources.
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Laser-Scanning System pinpoints imperfections in solar cells. Entire solar panels containing large numbers of cells can be scanned. Although technique is similar to use of scanning electron microscope (SEM) to locate microscopic imperfections, it differs in that large areas may be examined, including entire solar panels, and it is not necessary to remove cover glass or encapsulants.
We investigate the types and origins of structural defects in thin (<100 μm) kerfless epitaxial single crystal silicon grown on top of reorganized porous silicon layers. Although the structural defect density is low (has average defect density < 10 4 cm -2 ), localized areas with a defect density > 10 5 cm -2 are observed. Cross-sectional and systematic plan-view defect etching and microscopy reveals that the majority of stacking faults and dislocations originate at the interface between the porous silicon layer and the epitaxial wafer. Localised dislocation clusters are observed in regions of collapsed/deformed porous silicon and at decorated stacking faults. In localized regions of high extended defect density, increased minority-carrier recombination activity is observed. Evidence for impurity segregation to the extended defects (internal gettering), which is known to exacerbate carrier recombination is demonstrated. In conclusion, the impact of the defects on material performance and substrate re-use is also discussed.
Flexure test eliminates failure-prone wafers before further processing. Probability of cracking of silicon solar cells substantially reduced by mechanical proof testing of silicon wafers before further processing, according to report. Report based on study demonstrating weak wafers eliminated by subjecting all wafers in manufacturing batch to biaxial-flexure test.
Defect production in silicon is modeled on a computer by solving a large system of rate equations. The model includes the main, known defects that are stable at operating temperatures of solar cells in outer space; most of these defects are secondary and tertiary defects. The preliminary result shows that the presence of defect recombination centers for primary defects (i.e., vacancy and interstitial) can effectively reduce the production rates of those stable defects and, consequentially, improve the lifetime of solar cells operating in radiation environment. The characteristics of the defect recombination center required for better solar cell performance along with prospective candidates are discussed.
Defect passivation constitutes one of the most commonly used strategies to fabricate highly efficient perovskite solar cells (PSCs). However, the durability of the passivation effects under harsh operational conditions has not been extensively studied regardless of the weak and vulnerable secondary bonding between the molecular passivation agents and perovskite crystals. Here, we incorporated strategically designed passivating agents to investigate the effect of their interaction energies on the perovskite crystals and correlated these with the performance and longevity of the passivation effects. We unraveled that the passivation agents with a stronger interaction energy are advantageous not only for effective defect passivation but also to suppress defect migration. The prototypical PSCs treated with the optimal passivation agent exhibited superior performance and operational stability, retaining 81.9 and 85.3% of their initial performance under continuous illumination or nitrogen at 85 °C after 1008 h, respectively, while the reference device completely degraded during that time. Furthermore, this work provides important insights into designing operationally durable defect passivation agents for perovskite optoelectronic devices.
Defect states influence the operation of organic solar cells altering transport, recombination, and energetic mechanisms. This work investigates how processing conditions induce morphology-related, electrically active defects in the donor polymer of bulk-heterojunction solar cells. Structural order is inferred from absorption and X-ray diffraction data, while defect density is determined from capacitance methods. A correlation is observed between the polymer nanocrystallite size, the defect concentration, and the output voltage. For the case of poly(3-hexylthiophene), processing that promote crystallinity is beneficial for the device performance as it decreases the defect density (energy disorder) that finally enlarges the maximum achievable open-circuit voltage. Defect states within the effective bandgap modulate the downshift of the hole Fermi level upon illumination that in turn establishes the achievable open-circuit voltage.
Defects and annealing in electron irradiated lithium diffused silicon solar cells
Defects and impurities in halide perovskite solar cells can negatively impact device performance and long-term stability. In this study, we identify photonically cured methylammonium (MA) lead iodide films contain a residual adduct, MA 2 Pb 3 I 8 (dimethyl sulfoxide) 2 (MA 2 Pb 3 I 8 (DMSO) 2 ), that reduces photocurrent generation in perovskite solar cells (PSCs). This is evidenced by a decrease in the external quantum efficiency (EQE) near 400 nm. Similar EQE reductions were observed in PSCs produced using high-speed processes but have not been thoroughly examined. Through X-ray diffraction patterns and Fourier transform infrared spectroscopy, we establish the photo-inactive MA 2 Pb 3 I 8 (DMSO) 2 as the culprit for the EQE reduction. Combined experimental and simulation results reveal that the MA 2 Pb 3 I 8 (DMSO) 2 phase is located at the hole transport layer/ interface, not on the surface, resulting in lower quantum efficiency and surface photovoltage in the short wavelength region. The residual adduct is kinetically trapped due to the short processing time (20 ms) and crystallization direction but can be removed by an additional photonic pulse. Furthermore, this study highlights the need for careful examination of resulting materials beyond device efficiency when transitioning from laboratory processing to industrial high-speed methods.
Defect behavior, observed by deep level transient spectroscopy (DLTS), is used to predict carrier removal and the effects of simultaneous electron irradiation and injection annealing of the performance of InP solar cells. For carrier removal, the number of holes trapped per defect is obtained from measurements of both carrier concentrations and defect concentrations during an isochronal anneal. In addition, from kinetic considerations, the behavior of the dominant defect during injection annealing is used to estimate the degradation expected from exposure to the ambient electron environment in geostationary orbit.
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We demonstrate a self-consistent numerical scheme for simulating an electronic device which contains active defects. As a specific case, we consider copper defects in cadmium telluride solar cells. The presence of copper has been shown experimentally to play a crucial role in predicting device performance. The primary source of this copper is migration away from the back contact during annealing, which likely occurs predominantly along grain boundaries. We introduce a mathematical scheme for simulating this effect in 2D and explain the numerical implementation of the system. Finally, we will give numerical results comparing our results to known 1D simulations to demonstrate the accuracy of the solver and then show results unique to the 2D case.
A high efficiency configuration for a solar cell module comprises solar cells arranged in a shingled manner to form super cells, which may be arranged to efficiently use the area of the solar module, reduce series resistance, and increase module efficiency. Removing a defective solar cell from a super cell may be difficult, however. It may therefore be advantageous to bypass defective solar cells in a super cell rather than remove and replace them. A bypass conductor may be applied to the rear surface of the super cell to bypass one or more defective solar cells in a super cell or in a solar module comprising super cells.
Point defects directly impact solar cell device performance by limiting the carrier lifetime. In this work, density functional theory calculations are first used to determine the formation energy and diffusion energy barriers of dominant defects in Cu(In,Ga)Se 2 . Next, continuum reaction–diffusion models are developed to analyze the redistribution of defects during manufacturing processes. We estimate defect capture cross sections using a first-principles-based approach. Here, these cross sections are combined with our calculated defect profiles and trap energy levels to parameterize a Shockley–Read–Hall recombination model, which we implement into a device simulator to predict carrier lifetimes and device performance. In that way, a predictive technology computer aided design model is built to predict and optimize the performance of Cu(In,Ga)Se 2 solar cells.
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Correction for ‘A hole-transport material that also passivates perovskite surface defects for solar cells with improved efficiency and stability’ by Xiaoming Zhao et al. , Energy Environ. Sci. , 2020, 13 , 4334–4343, https://doi.org/10.1039/D0EE01655A.
The microstructure of as-grown and processed, edge-defined film-fed grown, silicon ribbons was studied in order to identify the basic mechanisms responsible for the change of the as-grown defect structure during processing at elevated temperatures. The short heat treatment required to diffuse the p-n junction was sufficient to cause heterogeneous precipitation of impurity atoms, particularly transition metals. In addition, an elastic recovery of the ribbon occurred by dislocation glide, resulting in the formation of a polygonizationlike structure of subboundaries in the base. Mechanisms are suggested by which twin boundaries, acting as dislocation obstacles, can concentrate the relatively low average dislocation densities typical of edge-defined film-fed grown ribbons (10 to the 4th to 10 to the 8th/sq cm) to values which are sufficient to induce the formation of subgrainlike boundary structures.
The results of studying the crystal structure of regions in silicon, recrystallized during the course of thermomigration of the liquid Si–Al zone in the volume of the silicon substrate, are reported (similar regions doped with an acceptor impurity are used to obtain high-voltage solar cells). X-ray methods (including measurements of both diffraction-reflection curves and topograms) and also high-resolution electron microscopy indicate that single-crystal regions in the form of a series of thin strips or rectangular grids are formed as a result of the thermomigration of liquid zones. Dislocation half-loops are detected in the surface layers of the front and back surfaces of the substrate. (311)-type defects are observed in the recrystallized regions.