Do lomer dislocations spoil high performance of mc-Si solar cells?

Material induced inherent efficiency losses of multicrystalline silicon solar cells have been investigated across all scales from the solar cell down to the atomic structure of the responsible crystallographic defects. Material inherent efficiency losses can be attributed to local increased dark current, which is found at recombination active small angle grain boundaries and accounts to several per-cent absolute. Aone-to-one correlation between the density of Lomer dislocations and the strength of the recombination activity of small angle grain boundaries is found by electron-beam induced current measurements and scanning transmission electron microscope investigations. The increased recombination activity of Lomer dislocations is attributed to their immobile nature, which favors contamination by impurities.publishe

Recombination at Lomer Dislocations in Multicrystalline Silicon for Solar Cells

Lomer dislocations at small-angle grain boundaries in multicrystalline silicon solar cells have been identified as responsible for the dominating inherent dark current losses. Resulting efficiency losses have been quantified by dark lock-in thermography to be locally up to several percent absolute, reducing the maximum power of the cells. By electron beam induced current measurements and scanning transmission electron microscopy investigations, it is revealed that the strengths of the dark current losses depend on the density of Lomer dislocations at the small-angle grain boundaries.publishe

Nanoscale Bi2FeO6−x precipitates in BiFeO3 thin films : a metastable Aurivillius phase

We report the observation of nano-scale precipitates corresponding to a new structure not displayed by the phase diagram of bismuth iron oxide. BiFeO3 (BFO) thin films grown on terbium scandate and strontium titanate substrates by pulsed laser deposition were investigated using high-resolution transmission and scanning transmission electron microscopy. Precipitate-like structures with a so far unknown metastable phase of bismuth, iron, and oxygen were observed in these films. They consist of well-ordered Bi2O2 layers, as they are known from bismuth oxide layered compounds. They have a pseudo-orthorhombic structure with a single perovskite-like unit (FeO6) sandwiched between Bi2O2 layers, similar to the Aurivillius phase Bi2WO6, with a chemical composition of the precipitates of Bi2FeO6−x . The structure of the new phase with its lattice constants was elucidated and the band gap of the precipitates was determined by electron energy loss spectroscopy. The results point to promising future applications for this new phase in the field of electronics, if it might be grown phase pure as an epitaxial thin film

Spin-state transition of iron in (Ba 0:5 Sr 0:5 ÞðFe 0:8 Zn 0:2 ÞO 3Àd perovskite

a b s t r a c t The redox behavior of iron during heating of a high-performance perovskite for ceramic oxygen separation membranes was studied by combined electron energy-loss (EELS, esp. ELNES) and Mössbauer spectroscopical in situ methods. At room temperature, the iron in ðBa 0:5 Sr 0:5 Þ ðFe 0:8 Zn 0:2 ÞO 3Àd (BSFZ) is in a mixed valence state of 75% Fe 4þ in the high-spin state and 25% Fe 3þ predominantly in the low-spin state. When heated to 900 3 C, a slight reduction of iron is observed that increases the quantity of Fe 3þ species. However, the dominant occurrence is a gradual transition in the spin-state of trivalent iron from a mixed low-spin/high-spin to a pure high-spin configuration. In addition, a remarkable amount of hybridization is found in the Fe-O bonds that are highly polar rather than purely ionic. The coupled valence/spin-state transition correlates with anomalies in thermogravimetry and thermal expansion behavior observed by X-ray diffraction and dilatometry, respectively. Since the effective cationic radii depend not only on the valence but also on the spin-state, both have to be considered when estimating under which conditions a cubic perovskite will tolerate specific cations. It is concluded that an excellent phase stability of perovskite-based membrane materials demands a tailoring, which enables pure high-spin states under operational conditions, even if mixed valence states are present. The low spin-state transition temperature of BSFZ provides that all iron species are in a pure high-spin configuration already above ca. 500 3 C making this ceramic highly attractive for intermediate temperature applications (5002800 3 C)

Coating the surface of interconnected Cu2O nanowire arrays with HKUST-1 nanocrystals via electrochemical oxidation

Abstract Controlling the crystallization of Metal–Organic Frameworks (MOFs) at the nanoscale is currently challenging, and this hinders their utilization for multiple applications including photo(electro)chemistry and sensors. In this work, we show a synthetic protocol that enables the preparation of highly homogeneous Cu2O@MOF nanowires standing on a conductive support with extensive control over the crystallization of the MOF nanoparticles at the surface of the Cu2O nanowires. Cu2O nanowires were first prepared via templated electrodeposition, and then partially converted into the well-known Cu-MOF HKUST-1 by pulsed electrochemical oxidation. We show that the use of PVP as a capping agent during the electrochemical oxidation of Cu2O into HKUST-1 provides control over the growth of the MOF nanocrystals on the surface of the Cu2O nanowires, and that the size of the MOF crystals obtained can be tuned by changing the concentration of PVP dissolved in the electrolyte. In addition, we propose the use of benzoic acid as an alternative to achieve control over the size of the obtained MOF nanocrystals when the use of a capping agent should be avoided

Amyloid-Beta Peptides Trigger Aggregation of Alpha-Synuclein In Vitro

Alzheimer’s disease (AD) and Parkinson’s disease (PD), including dementia with Lewy bodies (DLB), account for the majority of dementia cases worldwide. Interestingly, a significant number of patients have clinical and neuropathological features of both AD and PD, i.e., the presence of amyloid deposits and Lewy bodies in the neocortex. The identification of α-synuclein peptides in amyloid plaques in DLB brain led to the hypothesis that both peptides mutually interact with each other to facilitate neurodegeneration. In this article, we report the influence of Aβ(1–42) and pGlu-Aβ(3–42) on the aggregation of α-synuclein in vitro. The aggregation of human recombinant α-synuclein was investigated using thioflavin-T fluorescence assay. Fibrils were investigated by means of antibody conjugated immunogold followed by transmission electron microscopy (TEM). Our data demonstrate a significantly increased aggregation propensity of α-synuclein in the presence of minor concentrations of Aβ(1–42) and pGlu-Aβ(3–42) for the first time, but without effect on toxicity on mouse primary neurons. The analysis of the composition of the fibrils by TEM combined with immunogold labeling of the peptides revealed an interaction of α-synuclein and Aβ in vitro, leading to an accelerated fibril formation. The analysis of kinetic data suggests that significantly enhanced nucleus formation accounts for this effect. Additionally, co-occurrence of α-synuclein and Aβ and pGlu-Aβ, respectively, under pathological conditions was confirmed in vivo by double immunofluorescent labelings in brains of aged transgenic mice with amyloid pathology. These observations imply a cross-talk of the amyloid peptides α-synuclein and Aβ species in neurodegeneration. Such effects might be responsible for the co-occurrence of Lewy bodies and plaques in many dementia cases