Search results for " GAP"
showing 10 items of 811 documents
Fully Vacuum-Processed Wide Band Gap Mixed-Halide Perovskite Solar Cells
2017
Methylammonium lead mixed-halide perovskites MAPb(BrxI1–x)3 are promising materials for the preparation of tandem devices. When exposed to light, MAPb(BrxI1–x)3 segregates in iodide- and bromide-rich phases, limiting the achievable photovoltage and hence the attainable device efficiency. To date only solution-processed mixed-halide perovskites have been demonstrated. We present fully vacuum-deposited mixed-halide perovskite thin films with band gap of 1.72 and 1.87 eV, prepared by controlling the deposition rates of the different halide precursors. When used in thin-film devices, these materials lead to power conversion efficiencies of 15.9 and 10.5%, respectively, which are among the highe…
A new cross-linkable 9,10-diphenylanthracene derivative as a wide bandgap host for solution-processed organic light-emitting diodes
2018
Efficient organic light-emitting diodes (OLEDs) can be obtained using multilayered architectures where the processes of charge injection, transport and recombination are separated and optimized in each layer. Processing these structures from solution requires strategies to avoid redissolution or damage of the previously deposited layers. Several reports have demonstrated the development of cross-linkable hole transport materials, while less literature describes the synthesis and applications of such wide bandgap host materials for multilayered OLEDs. In this work we introduce a cross-linkable derivative of 9-(4-(10-phenylanthracene-9-yl)phenyl)-9H-carbazole incorporating styrene moieties (S…
Electronic structure of polysilanes: influence of substitution and conformation
1993
Abstract The valence effective Hamiltonian (VEH) quantum-chemical approach is used to investigate the electronic properties of polysilane. The valence band structure calculated for this fully saturated polymer is analyzed in terms of orbital contributions and compared to that of the closely related carbon polymer, polyethylene. The effects of alkyl substitution and silicon backbone conformation are studied by elucidating the modifications that these structural changes induce on the electronic valence band structure of all-trans unsubstituted polysilane. The VEH results predict a decrease of the band gap upon alkyl substitution and on going from helical to all-trans conformations.
Synthesis and characterization of a new Organic – Inorganic sulfate (C5H6N2O)2[Co(H2O)6]3(SO4)4.2H2O
2014
crystals of a new hybrid compound, (C 5 H 6 N 2 O) 2 [Co(H 2 O) 6 ] 3 (SO 4 ) 4 .2H 2 O, were synthesized in aqueous solution and characterized. This compound crystallizes in the triclinic system with the space group P-1, the unit cell :a=6.632(3) A, b=11.769(5) A, c=14.210(6) A, α=67.86(4)°, β=81.32(4)°, γ=85.18(4)° and V=1015.14(8) A 3 . Its crystal structure can be described as a packing of alternated inorganic and organic layers. The different components are connected by a three-dimensional network of O-H…O and N-H…O hydrogen bonds.
Effect of Mn Doping on the Optical Properties of Chalcogenide Compounds ZnS and ZnTe
2020
In this paper, the influence of the addition of Mn on the optical properties of the binary compounds ZnS and ZnTe deposited by a close-spaced vacuum sublimation method onto nonoriented glass at different substrate temperatures was considered. The spectral dependences of the transmittance T (λ), reflectance R (λ) and the absorption α (λ), as well as the bandgap for each material (Eg) were measured and calculated.
X-ray absorption near-edge structure of GaN with high Mn concentration grown on SiC.
2009
By means of x-ray absorption near-edge structure (XANES) several Ga(1-x)Mn(x)N (0.03x0.09) layers have been analyzed. The Mn-doped GaN samples consisted of different epilayers grown by molecular beam epitaxy on [0001] SiC substrates. The low mismatch between GaN and SiC allows for a good quality and homogeneity of the material. The measurements were performed in fluorescence mode around both the Ga and Mn K edges. All samples studied present a similar Mn ionization state, very close to 2+, and tetrahedral coordination. In order to interpret the near-edge structure, we have performed ab initio calculations using the full potential linear augmented plane wave method as implemented in the Wien…
On the low-lying singlet excited states of styrene: a theoretical contribution
2000
The present contribution analyses the trans–cis photoisomerization mechanism of ethene and styrene on the singlet manifold. Within the framework of multiconfigurational second-order perturbation theory (CASPT2), the extended multistate approach (MS-CASPT2) is found to be flexible enough to describe energy hypersurfaces adiabatically. For ethene, torsion about the CC bond towards a perpendicular structure leads to a situation where the energy difference between the ground and the lowest excited state is still too large (2.5 eV) for efficient radiationless decay. However, the energy gap decreases to 0.4 eV when one of the methylene moieties is, in addition, pyramidalized from the twisted stru…
Solubility-Driven Isolation of a Metastable Nonagold Cluster with Body-Centered Cubic Structure.
2020
The conventional synthetic methodology of atomically precise gold nanoclusters using reduction in solutions offers only thermodynamically most stable nanoclusters. We report herein a solubility‐driven isolation strategy to access the synthesis of a metastable gold cluster. The cluster, with the composition of [Au 9 (PPh 3 ) 8 ] + ( 1 ), displays an unusual, nearly perfect body‐centered‐cubic (bcc) structure. As revealed by ESI‐MS and UV/Vis measurement, the cluster is metastable in solution and converts to the well‐known [Au 11 (PPh 3 ) 8 Cl 2 ] + ( 2 ) within just 90 min. DFT calculations revealed that while both 1 and 2 are eight‐electron superatoms, there is a driving force to convert 1 …
ChemInform Abstract: Tuning the Band Gap of PbCrO4Through High-Pressure: Evidence of Wide-to-Narrow Semiconductor Transitions.
2014
Commercial polycrystalline and cleaved platelets from natural PbCrO4 are studied in a diamond anvil cell at ≤ 21 GPa.
Local banks and credit: from crisis to the new regulatory proposals for the development of lending policies in favour of the real economy
2014
Comparing the credit cooperative banks (CCBs) and banking groups operating in Italy, descriptive analyses show that the CCBs, unlike large banks, despite the economic downturn, have continued to extend credit to customers, but at the cost of a higher incidence of bad credit. This increased credit risk of local banks has been caused by management policy choices, such as the preference to modify the conditions applicable to credit supply and to engage firms in long-term credit relationships rather than initiate credit recovery procedures. An empirical analysis shows that this risk has also been caused by a higher incidence of environmental factors such as the spread of situations of crime and…