190 research outputs found
Exciton dynamics in hybrid polymer/QD blends
Abstract The prospect of exploiting quantum dots (QDs) properties (tunable absorption spectrum, multiple exciton generation) while maintaining the flexible structure of polymer systems opens new possibilities in the photovoltaic field. Although charge transport dynamics in pristine polymer and QDs systems have been quite well established lately, a complete understanding of the charge transfer process between QDs and polymers when they are in blends is still lacking. In this work we used static and ultrafast fluorescence spectroscopy together with Atomic force Microscopy (AFM) to study the exciton dynamics in polymer/QDs films. Specifically we used poly(3-hexylthiophene) (P3HT) as the hole conducting donor material and the core shell CdSe(ZnS) QDs as the electron acceptor material. The QDs surface has been treated with two different capping ligands treatments: one based on the use of pyridine and the other one on hexanoic acid. The influence of the two different methods on the exciton dynamics and on the morphology will also be discussed. Blends containing differently treated P3HT/CdSe(ZnS) wt% ratios have been prepared producing films having uniform morphology and good intermixing, as proved by AFM measurements. Ultrafast fluorescence decays allowed us to compare the exciton dynamics in the polymer pristine respect to the treated P3HT/CdSe(ZnS) films. Efficient fluorescence quenching has been shown by both kind of blends respect to the pure polymer
Understanding the Enhanced Stability of Bromide Substitution in Lead Iodide Perovskites
Lead halide perovskites have rapidly emerged as candidate materials for high-performing solar cells, but show serious issues related to long-term stability. Methylammonium (MA) lead perovskites with mixed iodide-bromide compositions, MAPb(I1-xBrx)3, are reported to exhibit improved stability, but the origin of such behavior is not fully understood. Here, we report new insights into the degradation properties of MAPb(I1-xBrx)3 using ab initio simulations and a range of spectroscopic techniques. Absorbance spectroscopy shows that as the Br content increases, the material stability toward oxygen and light increases. Isothermal gravimetric analysis and time-resolved single photon counting show that the amount of oxygen incorporation into perovskite films decreases significantly with increasing Br content. Ab initio simulations indicate that the degradation reaction involving superoxide species is energetically exothermic for pure MAPbI3 but becomes less favorable with increasing Br content with an endothermic energy for pure MAPbBr3, suggesting that the degradation of MAPbBr3 in the presence of oxygen and light is unfavorable. The simulations indicate shorter N-H...Br hydrogen bonds between the MA+ cation and Br ions, which would promote greater structural stability upon bromide substitution. Thin-film passivation with iodide salts is shown to enhance the stabilities of mixed-halide perovskite films and solar cell devices. The greater fundamental understanding of mixed iodide-bromide systems gained from this study is important for the future design of stable perovskite solar cells.</p
Synthesis and optical characterisation of triphenylamine-based hole extractor materials for CdSe quantum dots
Tobacco Smoke Carcinogens Induce DNA Repair Machinery Function Loss: Protection by Carbon Nanotubes
Purpose: DNA damage is a continuous process occurring within the cells caused by intrinsic and extrinsic factors, but it gets repaired regularly. If the DNA repair process is faulty, the incidences of damages/mutations can accumulate in cells resulting in cell transformation. It is hypothesized that the negative variations in DNA repair pathways in even at one point viz. genetic, translational or posttranslational stage may fairly be crucial for the beginning and development of carcinogenesis. Therefore, we investigated the potential of tobacco specific nitrosamines (TSNs) related carcinogens to interact with the enzymes involved in DNA repair mechanisms in the current study.
Methods: The derivatives of cigarettes’ smoke like NNK and NNAL are very well known and recognized carcinogens. Therefore, almost 120 enzymes playing crucial role in the DNA repair process have been analysed for their reactivity with NNK and NNAL.
Results: The molecular docking study helped to screen out, 07 possible DNA repair enzyme targets for NNK, and 12for NNAL. Present study revealed the loss of activity of DNA repair enzymes in the presence of NNK and NNAL, and this accumulation may induce the tendency of DNA damage which can lead the transformation of exposed normal cells in to cancerous cells. This study also demonstrated the protective potential of nanoparticles like SWCNTs/MWCNTs against TSN’s induced toxicity; here SWCNT against NNK (-17.16 Kcal/Mol) and MWCNT against NNK -17.01 Kcal/Mol were showing maximum binding affinities than the known biomolecular target of NNK 1UGH (Uracil-DNA glycosylase,-7.82Kcal/Mol).
Conclusion: CNTs can be applied as chemo-preventive agents against environmental and tobacco induced carcinogens owing to their scavenging potential and warrants for in vivo and in vitro experimental validation of the results obtained from the present study
State selective electron injection in non-aggregated titanium phthalocyanine sensitised nanocrystalline TiO2 films
We describe a novel titanium phthalocyanine that shows no aggregation when anchored to nanocrystalline TiO2 films through its axial carboxylated ligand without the use of co-adsorbents; state selective electron injection into the TiO2 is demonstrated, resulting in efficient photocurrent generation in dye sensitised photoelectrochemical solar cells.Palomares Gil, Emilio J, [email protected]
Polymeric hole-transport materials with side-chain redox-active groups for perovskite solar cells with good reproducibility
Sustainable green approach to synthesize Fe 3 O 4 /α-Fe 2 O 3 nanocomposite using waste pulp of Syzygium cumini and its application in functional stability of microbial cellulases
Synthesis of nanomaterials following green routes have drawn much attention in recent years due to the low cost, easy and eco-friendly approaches involved therein. Therefore, the current study is focused towards the synthesis of Fe(3)O(4)/α-Fe(2)O(3) nanocomposite using waste pulp of Jamun (Syzygium cumini) and iron nitrate as the precursor of iron in an eco-friendly way. The synthesized Fe(3)O(4)/α-Fe(2)O(3) nanocomposite has been extensively characterized through numerous techniques to explore the physicochemical properties, including X-ray diffraction, Fourier transform infrared spectroscopy, Raman spectroscopy, Ultraviolet-Vis spectroscopy, field emission scanning electron microscope, high resolution transmission electron microscope and vibrating sample magnetometer. Further, efficiency of the Fe(3)O(4)/α-Fe(2)O(3) nanocomposite has been evaluated to improve the incubation temperature, thermal/pH stability of the crude cellulase enzymes obtained from the lab isolate fungal strain Cladosporium cladosporioides NS2 via solid state fermentation. It is found that the presence of 0.5% Fe(3)O(4)/α-Fe(2)O(3) nanocomposite showed optimum incubation temperature and thermal stability in the long temperature range of 50–60 °C for 15 h along with improved pH stability in the range of pH 3.5–6.0. The presented study may have potential application in bioconversion of waste biomass at high temperature and broad pH range
The origin of slow electron recombination processes in dye-sensitized solar cells with alumina barrier coatings
We investigate the effect of a thin alumina coating of nanocrystalline TiO2 films on recombination dynamics of dye-sensitized solar cells. Both coated and uncoated cells were measured by a combination of techniques: transient absorption spectroscopy, electrochemical impedance spectroscopy, and open-circuit voltage decay. It is found that the alumina barrier reduces the recombination of photoinjected electrons to both dye cations and the oxidized redox couple. It is proposed that this observed retardation can be attributed primarily to two effects: almost complete passivation of surface trap states in TiO2 that are able to inject electrons to acceptor species, and slowing down by a factor of 3–4 the rate of interfacial charge transfer from conduction-band [email protected]
- …