Bifacial Passivation of Organic Hole Transport Interlayer for NiO x -Based p-i-n Perovskite Solar Cells.

Methoxy-functionalized triphenylamine-imidazole derivatives that can simultaneously work as hole transport materials (HTMs) and interface-modifiers are designed for high-performance and stable perovskite solar cells (PSCs). Satisfying the fundamental electrical and optical properties as HTMs of p-i-n planar PSCs, their energy levels can be further tuned by the number of methoxy units for better alignment with those of perovskite, leading to efficient hole extraction. Moreover, when they are introduced between perovskite photoabsorber and low-temperature solution-processed NiO x interlayer, widely featured as an inorganic HTM but known to be vulnerable to interfacial defect generation and poor contact formation with perovskite, nitrogen and oxygen atoms in those organic molecules are found to work as Lewis bases that can passivate undercoordinated ion-induced defects in the perovskite and NiO x layers inducing carrier recombination, and the improved interfaces are also beneficial to enhance the crystallinity of perovskite. The formation of Lewis adducts is directly observed by IR, Raman, and X-ray photoelectron spectroscopy, and improved charge extraction and reduced recombination kinetics are confirmed by time-resolved photoluminescence and transient photovoltage experiments. Moreover, UV-blocking ability of the organic HTMs, the ameliorated interfacial property, and the improved crystallinity of perovskite significantly enhance the stability of PSCs under constant UV illumination in air without encapsulation.

Structural, photophysical, and theoretical studies of imidazole-based excited-state intramolecular proton transfer molecules.

Imidazole-based excited state intramolecular proton transfer (ESIPT) blue fluorescent molecules, 2-(1-(4-chlorophenyl)-4,5-diphenyl-1H-imidazol-2-yl)phenol (BHPI-Cl) and 2-(1-(4-bromophenyl)-4,5-diphenyl-1H-imidazol-2-yl)phenol (BHPI-Br) were designed and synthesized by Debus-Radziszewski method through a one-pot multicomponent reaction in high yield. The synthesized compounds were fully characterized by 1H NMR, 13C NMR, FT-IR, FT-Raman, GC-Mass, and elemental analysis. The molecular structures in single crystal lattice were studied by X-ray crystallographic analysis. Because of the intramolecular hydrogen bonding, hydroxyphenyl group is planar to the central imidazole ring, while the other phenyl rings gave distorted conformations to the central heterocyclic ring. BHPI-Cl and BHPI-Br molecules showed intense ESIPT fluorescence at 480nm, because the two twisted phenyl rings on 4- and 5-positions have reduced intermolecular interaction between adjacent molecules in each crystal through a head-to-tail packing manner. Quantum chemical calculations of energies were carried out by (TD-)DFT using B3LYP/6-31G(d, p) basis set to predict the electronic absorption spectra of the compounds, and they showed good agreement between the computational and the experimental values. The thermal analyses of the synthesized molecules were also carried out by TGA/DSC method.

Management of transition dipoles in organic hole-transporting materials under solar irradiation for perovskite solar cells.

In organic hole-transporting material (HTM)-based p-i-n planar perovskite solar cells, which have simple and low-temperature processibility feasible to flexible devices, the incident light has to pass through the HTM before reaching the perovskite layer. Therefore, photo-excited state of organic HTM could become important during the solar cell operation, but this feature has not usually been considered for the HTM design. Here, we prove that enhancing their property at their photo-excited states, especially their transition dipole moments, can be a methodology to develop high efficiency p-i-n perovskite solar cells. The organic HTMs are designed to have high transition dipole moments at the excited states and simultaneously to preserve those property during the solar cell operation by their extended lifetimes through the excited-state intramolecular proton transfer process, consequently reducing the charge recombination and improving extraction properties of devices. Their UV-filtering ability is also beneficial to enhance the photostability of devices.

Moyamoya disease with cerebral arteriovenous malformation presenting as primary subarachnoid hemorrhage.

The authors report a rare combination of definite moyamoya disease and brain arteriovenous malformation (AVM) presenting with primary subarachnoid hemorrhage (SAH) unheard of in the literature. The authors review the radiographic findings of this unique case with a brief review of literature.

Clinical applications of susceptibility weighted MR imaging of the brain - a pictorial review.

INTRODUCTION: Susceptibility-weighted imaging (SWI) is a novel magnetic resonance (MR) technique that exploits the magnetic susceptibility differences of various tissues, such as blood, iron and calcification. This pictorial review covers many clinical conditions illustrating its usefulness. METHODS: SWI consists of using both magnitude and phase images from a high-resolution, three-dimensional fully velocity-compensated gradient echo sequence. Phase mask is created from the MR phase images, and multiplying these with the magnitude images increase the conspicuity of the smaller veins and other sources of susceptibility effects, which is depicted using minimal intensity projection (minIP). RESULTS: The phase images are useful in differentiating between diamagnetic and paramagnetic susceptibility effects of calcium and blood, respectively. This unique MR sequence will help in detecting occult low flow vascular lesions, calcification and cerebral microbleed in various pathologic conditions and aids in characterizing tumors and degenerative diseases of the brain. This sequence also can be used to visualize normal brain structures with conspicuity. CONCLUSION: Susceptibility-weighted imaging is useful in differentiating and characterizing diverse brain pathologies.

Hereditary spastic paraplegia with a thin corpus callosum.

We report a 15-year-old boy with autosomal recessive complicated hereditary spastic paraplegia with a thin corpus callosum (HSP-TCC). The involvement of the corpus callosum was characteristic with the genu and body predominantly affected with relative sparing of the splenium. HSP-TCC is being increasingly recognized over a wider geographical area than earlier believed. We now report a case of HSP-TCC from the Indian subcontinent.