Modification of carbon nitride based polymeric 2D materials for tailoring their optical, electronic and chemical properties for various applications has gained significant interest. The present report demonstrates the synthesis of a novel modified carbon nitride framework with a remarkable 3:5 C:N stoichiometry (C3N5) and an electronic bandgap of 1.76 eV, by thermal deammoniation of the melem hydrazine precursor. Characterization revealed that in the C3N5 polymer, two s-heptazine units are bridged together with azo linkage, which constitutes an entirely new and different bonding fashion from g-C3N4 where three heptazine units are linked together with tertiary nitrogen. Extended conjugation due to overlap of azo nitrogens and increased electron density on heptazine nucleus due to the aromatic π network of heptazine units lead to an upward shift of the valence band maximum resulting in bandgap reduction down to 1.76 eV. XRD, He-ion imaging, HR-TEM, EELS, PL, fluorescence lifetime imaging, Raman, FTIR, TGA, KPFM, XPS, NMR and EPR clearly show that the properties of C3N5 are distinct from pristine carbon nitride (g-C3N4). When used as an electron transport layer (ETL) in MAPbBr3 based halide perovskite solar cells, C3N5 outperformed g-C3N4, in particular generating an open circuit photovoltage as high as 1.3 V, while C3N5 blended with MA x FA1–x Pb­(I0.85Br0.15)3 perovskite active layer achieved a photoconversion efficiency (PCE) up to 16.7%. C3N5 was also shown to be an effective visible light sensitizer for TiO2 photoanodes in photoelectrochemical water splitting. Because of its electron-rich character, the C3N5 material displayed instantaneous adsorption of methylene blue from aqueous solution reaching complete equilibrium within 10 min, which is significantly faster than pristine g-C3N4 and other carbon based materials. C3N5 coupled with plasmonic silver nanocubes promotes plasmon-exciton coinduced surface catalytic reactions reaching completion at much low laser intensity (1.0 mW) than g-C3N4, which showed sluggish performance even at high laser power (10.0 mW). The relatively narrow bandgap and 2D structure of C3N5 make it an interesting air-stable and temperature-resistant semiconductor for optoelectronic applications while its electron-rich character and intrasheet cavity make it an attractive supramolecular adsorbent for environmental applications.

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Abstract.High spin polarization materials or spin filters are key components in spintronics, a niche subfield of electronics where carrier spins play a functional role. Carrier transmission through these materials is "spin selective" i.e. these materials are able to discriminate between "up" and "down" spins. Common spin filters include transition metal ferromagnets and their alloys, with typical spin selectivity (or, polarization) ~ 50% or less. Here we consider carrier transport in an archetypical one-dimensional molecular hybrid in which a single wall carbon nanotube (SWCNT) is wrapped around by single stranded deoxyribonucleic acid (ssDNA). By magnetoresistance measurements we show that this system can act as a spin filter with maximum spin polarization approaching ~ 74% at low temperatures, significantly larger than transition metals under comparable conditions. Inversion asymmetric helicoidal potential of the charged ssDNA backbone induces a Rashba spin-orbit interaction in the SWCNT channel and polarizes carrier spins. Our results are consistent with recent theoretical work that predicted spin dependent conductance in ssDNA-SWCNT hybrid. Ability to generate highly spin polarized carriers using molecular functionalization can lead to magnet-less and contactless spintronic devices in the future. This can eliminate the conductivity mismatch problem and open new directions for research in organic spintronics. 2 1. Introduction.

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Heterojunctions of the low bandgap semiconductor bismuth oxyiodide (BiOI) with bulk multilayered graphitic carbon nitride (g-C3N4) and few layered graphitic carbon nitride sheets (g-C3N4-S) are synthesized and investigated as an active photoanode material for sunlight driven water splitting.

Using ab initio hybrid density functional theory based calculations, we report here the electronic and geometric structure properties of three different types of single-walled zigzag silicon carbide nanotube simulated by finite clusters with dangling bonds saturated by hydrogen atoms. These three types differ in the spatial arrangements of Si and C atoms. Full geometry and spin optimizations have been performed without any symmetry constraints. A detailed comparison of the structures and stabilities of the three types of nanotube is presented. Our calculations show type 1 structures to be more stable than type 2 structures, consistent with another result found in the literature. The cohesive energies/atom of the newly proposed type 3 nanotubes lie in between type 1 and type 2. The dependence of the electronic band gaps on the respective tube diameters, energy density of states and dipole moments as well as Mulliken charge distributions have been investigated. For all types of nanotube, Si atoms moved outward of the tube axis making two concentric cylinders of Si and C atoms after relaxation, contrary to some published results in the literature for type 1 zigzag nanotubes. The band gaps for type 1 and type 2 nanotubes show an oscillatory pattern as the diameter increases. Unlike the other two types, the band gap for type 3 nanotubes decreases monotonically with increasing tube diameter. All the tubes studied here appear to have triplet ground states except for type 1 (3, 0). It is expected that these tubes with significant surface reconstructions, varieties of band gaps, and magnetic properties would have interesting and important applications in the field of band gap engineering and molecular electronics.

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Leading edge p-i-n type halide perovskite solar cells (PSCs) severely underperform n-i-p PSCs. p-i-n type PSCs that use PEDOT:PSS hole transport layers (HTLs) struggle to generate open-circuit photovoltage values higher than 1 V. NiO HTLs have shown greater promise in achieving high V oc values albeit inconsistently. In this report, a NiO nanomesh with Ni3+ defect grown by the hydrothermal method was used to obtain PSCs with V oc values that consistently exceeded 1.10 V (champion V oc = 1.14 V). A champion device photoconversion efficiency of 17.75% was observed. Density functional theory modeling was used to understand the interfacial properties of the NiO/perovskite interface. The PCE of PSCs constructed using the Ni3+-doped NiO nanomesh HTL was ∼34% higher than that of conventional compact NiO-based perovskite solar cells. A suite of characterization techniques such as transmission electron microscopy, field emission scanning electron microscopy, intensity-modulated photocurrent spectroscopy, intensity-modulated photovoltage spectroscopy, time-resolved photoluminescence, steady-state photoluminescence, and Kelvin probe force microscopy provided evidence of better film quality, enhanced charge transfer, and suppressed charge recombination in PSCs based on hydrothermally grown NiO nanostructures.