Dye-sensitized solar cells: Atomic scale investigation of interface structure and dynamics

Recent progress in dye-sensitized solar cells(DSC) research is reviewed, focusing on atomic-scale investigations of the interface electronic structures and dynamical processes, including the structure of dye adsorption onto TiO2, ultrafast electron injection, hot-electron injection, multiple-exciton generation, and electron–hole recombination. Advanced experimental techniques and theoretical approaches are briefly summarized, and then progressive achievements in photovoltaic device optimization based on insights from atomic scale investigations are introduced. Finally, some challenges and opportunities for further improvement of dye solar cells are presented.     

The 5f localization/delocalization in square and hexagonal americium monolayers: a FP-LAPW electronic structure study

The electronic and geometrical properties of bulk americium and square and hexagonal americium monolayers have been studied with the full-potential linearized augmented plane wave (FP-LAPW) method. The effects of several common approximations are examined: (1) non-spin polarization (NSP) vs. spin polarization (SP); (2) scalar-relativity (no spin-orbit coupling (NSO)) vs. full-relativity (i.e., with spin-orbit (SO) coupling included); (3) local-density approximation (LDA) vs. generalized-gradient approximation (GGA). Our results indicate that both spin polarization and spin orbit coupling play important roles in determining the geometrical and electronic properties of americium bulk and monolayers. A compression of both americium square and hexagonal monolayers compared to the americium bulk is also observed. In general, the LDA is found to underestimate the equilibrium lattice constant and give a larger total energy compared to the GGA calculations. While spin orbit coupling shows a similar effect on both square and hexagonal monolayer calculations regardless of the model, GGA versus LDA, an unusual spin polarization effect on both square and hexagonal monolayers is found in the LDA results as compared with the GGA results. The 5f delocalization transition of americium is employed to explain our observed unusual spin polarization effect. In addition, our results at the LDA level of theory indicate a possible 5f delocalization could happen in the americium surface within the same Am II (fcc crystal structure) phase, unlike the usually reported americium 5f delocalization which is associated with crystal structure change. The similarities and dissimilarities between the properties of an Am monolayer and a Pu monolayer are discussed in detail.     

The mechanical,thermodynamic and electronic properties of Al3Nb with DO22 structure: A first-principles study

The lattice constants, elastic properties, electronic structure and thermodynamic properties of Al₃Nb with DO₂₂ structure have been investigated by the first-principles calculation. The calculated lattice constants were consistent with the experimental values, and the structural stability was also studied from the energetic point of view. The single-crystal elastic constants (C_ij) as well as polycrystalline elastic parameters (bulk modulus B, shear modulus G, Young's modulus E, Poisson's ratio υ and anisotropy value A) were calculated, and brittleness of Al₃Nb was discussed in detail. Besides, the electronic structure of tetragonal Al₃Nb was studied, which indicates a mixture of metallic bond and covalent bond in Al₃Nb and reveals the underlying mechanism of the stability and elastic properties of Al₃Nb. Finally, the thermodynamic properties of Al₃Nb were calculated and the physical properties such as heat capacity and Debye temperature were predicted within the quasi-harmonic approximation.     

Isolation and characterization of conformational isomers of N,N′‐bis(3,5‐dichlorosalicylidene)‐2,2′‐ethylenedianiline: crystal structure,photoluminescence, and density functional theory calculation

We have isolated two isomeric solids 1 and 2 of N,N′‐bis(3,5‐dichlorosalicylidene)‐2,2′‐ethylenedianiline and characterized by IR, UV/Vis, X‐ray powder diffraction, thermogravimetric analysis/differential thermal analysis, and X‐ray crystallography. Although the solids are same formulas, each shows different colors and crystal structures. Orange solid ( 1 ) shows endo conformation while yellow solid ( 2 ) exhibits exo form depending on packing modes. UV/Vis spectra of 1 and 2 appear very similar patterns in the solid state; however, the bands of 1 are slightly red‐shifted compared with those of 2 . 1 displays a strong fluorescent emission band at ~582 nm while 2 shows an intense fluorescent signal at ~563 nm. The charge density populations of 1 and 2 have been studied by computational simulations using density functional theory at pbe1pbe/6‐311G** level. The calculated highest occupied molecular orbital and lowest unoccupied molecular orbital energies of 1 and 2 confirm that charge transfer occurs within the organic molecules. The energy difference of HOMO‐LUMO in 1 is smaller slightly than that of 2 about 0.05 eV (~17 nm). Copyright © 2014 John Wiley & Sons, Ltd.     

Electronic and geometric structure of doped rare-gas clusters: surface, site and size effects studied with luminescence spectroscopy

The electronic and geometric structure of rare gas clusters doped with rare-gas atoms Rg = Xe, Kr or Ar is investigated with fluorescence excitation spectroscopy in the VUV spectral range. Several absorption bands are observed in the region of the first electronic excitations of the impurity atoms, which are related to the lowest spin-orbit split atomic ³P₁ and ¹P₁ states. Due to influence of surrounding atoms of the cluster, the atomic lines are shifted to the blue and broadened (“electronical cage effect”). From the known interaction potentials and the measured spectral shifts the coordination of the impurity atom in Ar_N, Kr_N, Ne_N and He_N could be studied in great detail. In the interior of Kr_N and Ar_N the Xe atoms are located in substitutional sites with 12 nearest neighbours and internuclear distances comparable to that of the host matrix. In Ne_N and He_N the cluster atoms (18 and 22, respectively) arrange themselves around the Xe impurity with a bondlength comparable to that of the heteronuclear dimer. The results confirm that He clusters are liquid while Ne clusters are solid for N≥ 300. Smaller Ne clusters exhibit a liquid like behaviour. When doping is strong, small Rg_m-clusters (Rg = Xe, Kr, Ar, m≤10 ²) are formed in the interior sites of the host cluster made of Ne or He. Specific electronically excited states, assigned to interface excitons are observed. Their absorption bands appear and shift towards lower energy when the cluster size m increases, according to the Frenkel exciton model. The characteristic bulk excitons appear in the spectra, only when the cluster radius exceeds the penetration depth of the interface exciton, which can be considerably larger than that in free Rg_m clusters. This effect is sensitive to electron affinities of the guest and the host cluster.     

Synthesis,spatial structure and spectral properties of pyrylo‐4 (thio) squaraines variously substituted in cyclobutene moiety

Synthetic routes have been developed to a number of (thio) squaraine dyes containing the residues of CH‐acids at the central cyclobutene ring. The electronic and spatial structure as well as the chemical conversions and optical behaviour of the compounds obtained have been studied both theoretically and by X‐ray diffraction analysis, ¹H NMR and electronic spectroscopy. As shown, the electronic nature and sterical characteristics of the central ring substituents give rise to some general conformational features and crystal packing regularities and also govern the spectral position of the first π–π^* absorption band. The structure–property relationships established in the study provide guidance for the purposeful design of deeply coloured (thio) squaraines. Copyright © 2015 John Wiley & Sons, Ltd.     

Tight-binding studies of surface effects on electronic structure of CdSe nanocrystals: the role of organic ligands, surface reconstruction, and inorganic capping shells

We utilize a tight-binding model to study the effects of surface structure on electronic properties of CdSe clusters. The model takes into account experimental information about structure and shape of the nanocrystals, as well as the nature and distribution of capping ligands. The effects of both organic capping ligands and inorganic capping shells on the densities of states (DOS) and on the single-particle absorption spectra of the clusters are calculated for various cluster shapes and sizes, and are compared to results for clusters with truncated surfaces. For organic capping ligands, the effect of ligand hybridization is investigated and a simple model of surface reconstruction is developed. Both ligand hybridization and surface reconstruction are seen to have a major influence on the band edge electronic and optical properties. Inorganic capping shells give rise to differential localization of valence and conduction band edge states, with the hole primarily confined to the core region and the electron more evenly distributed over both core and shell. Received 21 September 1998 / Received in final form: 15 December 1998     

Functional glycomics and evidence for gain- and loss-of-functions of target proteins for glycosyltransferases involved in N-glycan biosynthesis: their pivotal roles in growth and development,cancer metastasis and antibody therapy against cancer

N-Acetylglucosaminyltransferase V (GnT-V), N-acetylglucosaminyltransferase III (GnT-III) and α1-6 fucosyltransferase (Fut8) catalyze reactions that form biologically important branching N-linked sugar chains in glycoproteins. The above three branching N-glycan sugar chains, β1-6 GlcNAc branching, bisecting GlcNAc and core fucose (α1-6 fucose), play major roles in cancer invasion and metastasis, the inhibition of cancer metastasis, and antibody-dependent cellular cytotoxicity (ADCC), growth and development, respectively. A functional glycomic approach identified the gain- and loss-of-functions of glycoproteins as the result of the aberrant glycosylation. A membrane-type metal dependent serine proteinase designated matriptase which contains β1-6 GlcNAc branching became resistant to auto-digestion and proteolysis by trypsin, and resulted in a constitutively active form which might be implicated in cancer invasion and metastasis. GnT-V also acts as an angiogenic factor without the mediation of functions as a glycosyltransferase. Recently, a GnT-V homologue, GnT-IX has been identified. This gene is expressed at relatively high levels in the brain and acts on N-glycans to form a unique branched structure, as well as O-mannosyl glycans. The addition of bisecting GlcNAc to various signaling molecules or adhesion molecules suppresses cancer metastasis. Fut8 knock-out mice, due to the lack of a core fucose (α1-6 fucose) in target glycoproteins, show disorders in growth and development. The presence of a bisecting GlcNAc or the absence of a core fucose in IgG molecules enhances ADCC activity for killing tumor cells by up to 10 to 100 fold and therefore is thought to have considerable use in antibody therapy against cancer. These data clearly indicate that gain- and loss-of-functions of target proteins for these glycosyltransferases are biologically important.     

UV filter 2‐ethylhexyl 4‐methoxycinnamate: a structure,energetic and UV–vis spectral analysis based on density functional theory

2‐Ethylhexyl 4‐methoxycinnamate (EHMC) is a very commonly used UVB filter that is known to isomerize from the (E) to the (Z) isomer in the presence of light. In this study, we have performed high level quantum chemical calculations using density functional theory (DFT) with the B3LYP density functional and extended basis sets to study the gas‐phase molecular structure of EHMC and its energetic stability. Calculations were also performed for related smaller molecules cinnamic acid and 4‐methoxycinnamic acid. Charge delocalization has been analyzed using natural charges and Wiberg bond indexes within the natural bond orbital analysis and using nucleus independent chemical shifts. Density functional theory calculations reveal that the (E) isomer of EHMC is more stable than the (Z) by about 20 kJ mol^?1 in both the gas and aqueous phases. The enthalpy of formation in the gas phase of (E)‐EHMC was derived from an isodesmic bond separation reaction. Long‐range corrected DFT calculations in implicit water were made in order to understand the excited state properties of the (E) and (Z) isomers of EHMC. Copyright © 2013 John Wiley & Sons, Ltd.