Vinay Gupta

Efficient Solution‐Processed Small‐Molecule Solar Cells with Inverted Structure

We successfully demonstrate inverted structure small-molecule (SM) solar cells with an efficiency of 7.88% using ZnO and PEIE as an interfacial layer. Modification of ZnO with a cost-effective PEIE thin layer increases the efficiency of the inverted cell as a result of reducing the work function of the cathode and suppressing the trap-assisted recombination. In addition to the high efficiency, the inverted SM solar cells are relatively stable in air compared to conventional cells.

Polymer–Polymer Förster Resonance Energy Transfer Significantly Boosts the Power Conversion Efficiency of Bulk‐Heterojunction Solar Cells

Optically resonant donor polymers can exploit a wider range of the solar spectrum effectively without a complicated tandem design in an organic solar cell. Ultrafast Förster resonance energy transfer (FRET) in a polymer-polymer system that significantly improves the power conversion efficiency in bulk heterojunction polymer solar cells from 6.8% to 8.9% is demonstrated, thus paving the way to achieving 15% efficient solar cells.

Nickel(II) tetra-aminophthalocyanine modified MWCNTs as potential nanocomposite materials for the development of supercapacitors†

The supercapacitive properties of nickel(II) tetraaminophthalocyanine (NiTAPc)/multi-walled carbon nanotube (MWCNT) nanocomposite films have been interrogated for the first time and found to possess a maximum specific capacitance of 981 ± 57 F g−1 (200 ± 12 mF cm−2), a maximum power density of 700 ± 1 Wkg−1, a maximum specific energy of 134 ± 8 Wh kg−1 and excellent stability of over 1500 charge-discharge continuous cycling. Impedimetric study proves that most of the stored energy of the MWCNT-NiTAPc nanocomposite can be accessible at high frequency (720 Hz). When compared to MWCNTs modified with unsubstituted nickel(II) phthalocyanine (MWCNT-NiPc) or nickel(II) tetra-tert-butylphthalocyanine (MWCNT-tBuNiPc), MWCNT-NiTAPc exhibited superior supercapacitive behaviour, possibly due to the influence of nitrogen-containing groups on the phthalocyanine rings.

Antioxidant activity of fractionated extracts of rhizomes of high-altitude Podophyllum hexandrum: Role in radiation protection

Whole extract of rhizomes of Podophyllum hexandrum has been reported earlier by our group to render whole-body radioprotection. High-altitude P. hexandrum (HAPH) was therefore fractionated using solvents of varying polarity (non-polar to polar) and the different fractions were designated as, n-hexane (HE), chloroform (CE), alcohol (AE), hydro-alcohol (HA) and water (WE). The total polyphenolic content (mg% of quercetin) was determined spectrophotometrically, while. The major constituents present in each fraction were identified and characterized using LC-APCI/MS/MS. In vitro screening of the individual fractions, rich in polyphenols and lignans, revealed several bioactivities of direct relevance to radioprotection e.g. metal-chelation activity, antioxidant activity, DNA protection, inhibition of radiation (250 Gy) and iron/ascorbate-induced lipid peroxidation (LPO). CE exhibited maximum protection to plasmid (pBR322) DNA in the plasmid relaxation assay (68.09% of SC form retention). It also showed maximal metal chelation activity (41.59%), evaluated using 2,2′-bipyridyl assay, followed by AE (31.25%), which exhibited maximum antioxidant potential (lowest absorption unit value: 0.0389± 0.00717) in the reducing power assay. AE also maximally inhibited iron/ascorbate-induced and radiation-induced LPO (99.76 and 92.249%, respectively, at 2000 μg/ml) in mouse liver homogenate. Under conditions of combined stress (radiation (250 Gy) + iron/ascorbate), at a concentration of 2000 μg/ml, HA exhibited higher percentage of inhibition (93.05%) of LPO activity. HA was found to be effective in significantly (p < 0.05) lowering LPO activity over a wide range of concentrations as compared to AE. The present comparative study indicated that alcoholic (AE) and hydro-alcoholic (HA) fractions are the most promising fractions, which can effectively tackle radiation-induced oxidative stress.

Defect induced photoluminescence and ferromagnetic properties of bio-compatible SWCNT/Ni hybrid bundles.

Designing of bio-compatible nanomagnets with multiple functionalities receives immense scientific attention due to their potential applications in bio-labeling, medical diagnosis and treatment. Here we report the synthesis of Nickel (Ni) incorporated single-walled carbon nanotube (SWCNT) hybrid and bio-compatible bundles having interesting magnetic and photoluminescence (PL) properties. The SWCNT exhibits a high-crystallinity and it has an average diameter of ∼1.7 nm. Ni particles of 10-20 nm were incorporated within the SWCNT bundles. These hybrid bundles exhibit PL and it is attributed to the presence of delocalized π electrons and their recombination at the defective sites of SWCNT. Magnetic characterization revealed that the SWCNT/Ni hybrid bundle possesses a high (50 Oe) coercivity compared to bulk Ni and a long range ferromagnetic ordering at room temperature. MTT-assay has been conducted to study the cytotoxicity of these hybrid nanostructures.

An Organic Dyad Composed of Diathiafulvalene‐Functionalized Diketopyrrolopyrrole–Fullerene for Single‐Component High‐Efficiency Organic Solar Cells

A new low-band gap dyad DPP-Ful, which consists of covalently linked dithiafulvalene-functionalized diketopyrrolopyrrole as donor and fullerene (C60 ) as the acceptor, has been designed and synthesized. Organic solar cells were successfully constructed using the DPP-Ful dyad as an active layer. This system has a record power-conversion efficiency (PCE) of 2.2u2009%, which is the highest value when compared to reported single-component organic solar cells.

A high performance inverted organic solar cell with a low band gap small molecule (p-DTS(FBTTh2)2) using a fullerene derivative-doped zinc oxide nano-film modified with a fullerene-based self-assembled monolayer as the cathode

We have successfully integrated two effective strategies to improve the power conversion efficiency (PCE) of bulk heterojunction inverted small molecule solar cells (i-SMSCs) by doping a ZnO cathode with a fullerene derivative (ZnO–C60) followed by fullerene derivative self-assembled monolayer (SAM) modification on its surface in contact with the active layer. Such ZnO–C60 gives a fullerene-derivative-rich interface in contact with the active layer and enhanced surface conductivity relative to pristine ZnO (from 0.015 to 1.09 S cm−1) and bulk electron mobility (from 1.23 ± 0.39 × 10−4 to 6.43 ± 0.35 × 10−3 cm2 V−1 s−1). Using this ZnO–C60 as the cathode, the device with the active layer p-DTS(FBTTh2)2:PC71BM gives a higher PCE of 8.3% than that using ZnO without doping, 6.08%. Further incorporation of fullerene derivatives (NPC60-OH and NPC70-OH) as a SAM on ZnO–C60 effectively passivates the electron traps on the ZnO–C60 surface, resulting in increased electron mobility. The device using the ZnO–C60 nanofilm with phenol substituted C70 (NPC70-OH) as the SAM gives a further promoted PCE of up to 9.14%, which is the best value among the reported values in i-SMSCs.

Synergetic effect of CuS@ZnS nanostructures on photocatalytic degradation of organic pollutant under visible light irradiation

Ultrafast visible light active CuS/ZnS nanostructured photocatalysts were synthesized by a hydrothermal method. The effect of the CuS concentration on the morphological, structural and optical properties of ZnS nanostructures were investigated. X-ray diffraction analysis indicated the formation of CuS/ZnS phases with good crystallinity. The presence of ZnS on CuS was confirmed by X-ray photoelectron spectroscopy, elemental mapping, scanning electron microscopy and high resolution transmission electron microscopy analyses. CuS/ZnS nanocomposites efficiently decomposed methylene blue (MB) upon irradiation with visible light. The degradation time was 3 times faster than that of bare ZnS and CuS. The scavenger analysis results revealed that photogenerated superoxide (O2−˙) radicals were the main reactive species for the degradation of MB. The maximum degradation efficiency of 95.51% was observed within 5 min for samples of 0.050 M CuS/ZnS composites. The obtained results suggested that the enhanced photocatalytic activity was due to the formation of CuS/ZnS heterojunctions which led to the efficient separation of the photoinduced carriers.

Graphene as intermediate phase in fullerene and carbon nanotube growth: A Young–Laplace surface-tension model

Growth mechanism of carbon nanotubes using arc-discharge are not fully understood up to now. Here, I show that the formation of carbon nanotubes and fullerene in a pure carbon arc in helium atmosphere may involve graphene bubbles. Electron microscopy shows the graphene bubbles formation at the anode surface. The growth of fullerene and nanotubes can occur from these bubbles due to a large pressure difference (103–104u2002bar) at the anode interface and can be understood in terms of Young–Laplace law of surface tension. This model can explain the helium pressure dependence of fullerene and carbon nanotube formation.

Appearance of efficient luminescence energy transfer in doped orthovanadate nanocrystals

This paper reports the detailed synthesis mechanism and the structural, morphological and optical characterization of ultraviolet (similar to 311 nm) excitable samarium doped gadolinium yttrium orthovanadate, (Gd,Y)VO4:Sm3+, nanocrystals. X-ray diffraction and Rietveld refinement studies confirmed that the synthesized samples crystallize in a tetragonal structure with I41/amd space group. The enhanced photoluminescence intensity of (Gd, Y)VO4:Sm3+ compared with the existing YVO4:Sm3+ phosphor clearly indicates the significant role of Gd3+ ions. This has been attributed to the sensitization of the P-6(J) energy level of Gd3+ ions by energy transfer from orthovanadate (VO43-) ions and subsequent energy trapping by Sm3+ ions. The energy transfer from VO43 to Gd3+ via Gd3+ ions as intermediates and concentration quenching of Gd3+ luminescence are discussed in detail. The optical band gap of the as-prepared nanocrystals has been estimated using UV-vis-NIR absorption spectroscopy, which reveals a slightly higher band gap (3.75 eV) for YVO4 as compared to GdYVO4 (3.50 eV). Furthermore, confocal microcopy, decay parameters and Commission Internationale de lEclairage chromatic coordinates have supplemented these studies, which established the suitability of these nanophosphors for achieving spectral conversion in silicon solar cells.