Inverted Organic Solar Cells with Improved Performance using Varied Cathode Bu?er Layers

Organic solar cells with inverted planar heterojunction structure based on subphthalocya-nine and C₆₀ were fabricated using several kinds of materials as cathode buffer layer (CBL), including tris-8-hydroxy-quinolinato aluminum (Al_q3), bathophenanthroline (Bphen), bathocuproine, 2,3,8,9,14,15-hexakis-dodecyl-sulfanyl-5,6,11,12,17,18-hexaazatrinaphthylene (HATNA), and an inorganic compound of Cs₂CO₃. The influence of the lowest unoccupied molecular orbital level and the electron mobility of organic CBL on the solar cells perfor-mance was compared. The results showed that Al_q3, Bphen, and HATNA could significantly improve the device performance. The highest efficiency was obtained from device with an-nealed HATNA as CBL and increased for more than 7 times compared with device without CBL. Furthermore, the simulation results with space charge-limited current theory indicated that the Schottky barrier at the organic/electrode interface in inverted OSC structure was reduced for 27% by inserting HATNA CBL.     

Novel organogelators based on amine-derived hexaazatrinaphthylene

Novel C(3)-symmetrical heteroaromatic hexaazatrinaphthylene (HATNA) gelators symmetrically end-substituted with pendant aromatic and aliphatic amines were synthesized. Some of these π-conjugated structures induce self-assembly, forming fibers able to gelate solvents of different polarity at low wt% as demonstrated by spectroscopic and microscopic techniques.     

Analysis of operation mode of reflective liquid crystal display devices

The reflective liquid crystal display device having one polarizer was studied with the dynamic parameter space method. Device operation mode was analysed for both normally black and normally white operation conditions. The electro-optical responses and reflectance spectra were also studied for different operation modes. It was found that the optimized normally white modes for twist angles 180 degrees and 220 degrees of the reflective liquid crystal device have satisfactory contrast ratios and dispersion properties. For these twist angles, two equivalent normally white modes exist. The polarizer angles beta 1 of the first mode and beta 2 of the second mode have the simple relation beta 2 = 90 degrees + beta 1.     

Patterning of robust self-assembled n-type hexaazatrinaphthylene-based nanorods and nanowires by microcontact printing

The one-dimensional (1-D) self-assembly property of an n-type hexaazatrinaphthylene (HATNA) discotic pi-conjugated molecule was studied. Structurally robust unimolecular columnar stacks of HATNA with tunable length have been fabricated through a combination of supramolecular self-assembly and post-polymerization approach. Moreover, microcontact printing can be utilized to transfer the self-assembled nanostructures to the surface to create desired functional patterns.     

Analysis of operation mode of reflective liquid crystal display devices

The reflective liquid crystal display device having one polarizer was studied with the dynamic parameter space method. Device operation mode was analysed for both normally black and normally white operation conditions. The electro-optical responses and reflectance spectra were also studied for different operation modes. It was found that the optimized normally white modes for twist angles 180° and 220° of the reflective liquid crystal device have satisfactory contrast ratios and dispersion properties. For these twist angles, two equivalent normally white modes exist. The polarizer angles β₁ of the first mode and β₂ of the second mode have the simple relation β₂ = 90° + β₁.     

The conformations of bicyclo[3.1.0]hexane derivatives by 1H and 13C NMR

The ¹H and ¹³C spectra of bicyclo[3.1.0]hexanes and thujanes have been recorded and assigned. Application of the Karplus equation has yielded dihedral angles, and a computer calculation of the angle of ring buckle as a function of the main dihedral angles has been carried out. The calculated angles of ring buckle agree well with known values in the bicyclo[3.1.0]hexanes, but for 1-methylbicyclo[3.1.0]hexanes and thujanes the results are not self consistent. It is suggested that the bridgehead substituent causes the boat to twist, although the twist can be reduced by an axial methyl substituent on C-4.     

Calculating the energies for Ag(001) twist boundaries utilizing the modified analytical embedded atom method

The unrelaxed energies for Ag(001) twist grain boundaries (GBs) have been calculated using the modified analytical embedded atom method (MAEAM). The results show that, besides zero energy in a perfect crystal (corresponding to the twist angle 0°), the second smallest GB energy corresponds to the twist angle 36.87°. This is consistent with the experimental results. For other twist angles, the GB energies remain nearly constant even for a twist angle as small as 1.94°. Translation parallel to the boundary plane could result in a periodic change in GB energy. Copyright © 2004 John Wiley & Sons, Ltd.     

N-苄叉基-2-氨基噻唑及其类似物的构象和分子内的扭曲驱动力

确定了N-苄叉基-2-氨基噻唑(2a)和N-对硝基苄叉基-2-氨基噻唑(2b)的晶体结构.结合已报道的N-对硝基苄叉基-2-氨基嘧啶(1a),N-对硝基苄叉基-2-氨基吡啶(1b)和N-苄叉基-3-氨基吡啶(2c)的晶体结构,利用AM1,RHF,DFT方法和6-311G,6-311G^**基组,优化每个分子的22个旋转构象(θ=0°～90°).由DFT法所得到的最优构象的扭角θ(1a,22°;1b,0°;1c,42°;2a、2b:0°)与实验值(1a,26°;1b,20°;1c,46°;2a,8.8°;2b,3.8°)最接近.尽管分子最优构象扭角的差异很大,但总电子能最稳定的构象都在θ=±42°附近.在任一分子、任何电子态中,离域的π体系总是失稳定的,全平面构象不是π体系最稳定的构象.无论是离域的还是定域的π体系,它们均倾向于扭曲的几何构象.π电子的离域是分子扭曲的驱动力之一.与经典观点相反,非键原子间的核排斥作用是分子扭曲的阻力,而不是动力.     

Darstellung von tetraaryl-pyrrolen und vergleichende epr-g-faktor-untersuchung von pyrryl-radikalen mit tetracyclon-ketylen

The synthesis of a number of substituted tetraphenyl-pyrroles is presented. The electronic g-factors of the corresponding pyrryl radicals are measured by EPR techniques in solution. A linear relationship has been found between type and number of the substituents and the g-factor shift, Assuming a twist angle of 25° for the α- and 60° for the β-pheny] rings with respect to the plane of the five membered ring, the EPR data can be satisfactorily explained by means of HMO-McLachlan calculations. The twist angles of the phenyl rings in the analogous substituted tetracyclone-ketyl system which give the best fit to experiment are 65° for the α- and 20° for the β-phenyl rings, respectively. The different conformations found for the two systems can be explained by considering the different charge distributions in the pyrryl- and in the tetracyclone-ketyl-radicals.     

Effect of disorder in the twist angle on light scattering by a three-dimensional spherulite

Light scattering patterns are calculated for imperfect three-dimensional spherulites with fluctuations in the twist angle. The fluctuations are described in terms of a parameter characterizing the distance correlation function. Cases are considered in which (i) the principal axis of the scattering element makes a constant angle with the radius but there is disorder in the twist angle about the axis, and (ii) there is combined twist disorder and orientation disorder of the scattering elements. Calculations suggest that the disorder in the twist angle may lead to a decrease in the higher-order variation of scattered intensity with scattering angle and deviation from the four-leaf-clover-type scattering characteristic of a perfect spherulite at lower scattering angles. On the other hand, disorder in orientation has little effect on the scattering pattern.     

Hexaazatrinaphthylene Derivatives: Efficient Electron‐Transporting Materials with Tunable Energy Levels for Inverted Perovskite Solar Cells

Hexaazatrinaphthylene (HATNA) derivatives have been successfully shown to function as efficient electron‐transporting materials (ETMs) for perovskite solar cells (PVSCs). The cells demonstrate a superior power conversion efficiency (PCE) of 17.6 % with negligible hysteresis. This study provides one of the first nonfullerene small‐molecule‐based ETMs for high‐performance p–i–n PVSCs.     

Exploring the potential energy surface of retinal, a comparison of the performance of different methods

The ground state structure of retinal has been investigated. We found that DFT and CASSCF produce different results for the bond length alternation in a model system of retinal. Quantum mechanics/molecular mechanics calculations including the closest surrounding amino acids have been performed, using DFT and CASSCF to calculate the structure of retinal in the protein cavity. The planarity of the retinal molecule is affected by the surrounding protein. DFT and CASSCF produce different twist angles. The difference between CASSCF and DFT appears to be related to the positively charged nitrogen of the Schiff base, which leads to different pi-bond orders produced by the two methods.     

Delocalisation,conformation and basicity of anilines

¹³ C spectra of some anilines $\text{1}$ and annelated anilines $\text{2}$ are reported. Variations in the chemical shift of the para carbon atom are used to estimate twist angles of the amino group. Results so obtained are compared to base strength. It is found that in twisted anilines a rough correlation between twist angle and base strength exists.     

Epitaxy and lamellar twisting in transcrystalline polyethylene

The aim of this study was to investigate the micro structure of the transcrystalline interphase, obtained under isothermal conditions, in polyethylene-based single-polymer microcomposites. Analysis of the angular distribution of intensity in the X-ray diffraction patterns, obtained from transcrystalline layers of varying thickness, indicate that the transcrystalline growth most probably starts epitaxially with the c-axis of the orthorhombic unit cell aligned in the fiber axis direction. In the growth stage that follows, the lamellae twist as the crystals grow outward from the fiber surface, with the c-axis exhibiting variable angles with respect to the fiber axis for different transcrystalline layer thicknesses. The calculations based on the X-ray diffraction results, suggest that the pitch of the lamellar twist is 28.6 micrometers. © 1997 John Wiley & Sons, Inc. J Polym Sci B: Polym Phys 35 : 2429–2433, 1997     

Sterically Frustrated Aromatic Enes with Various Colors Originating from Multiple Folded and Twisted Conformations in Crystal Polymorphs**

Overcrowded ethylenes composed of 10-methyleneanthrone and two bulky aromatic rings contain a twisted carbon–carbon double (C=C) bond as well as a folded anthrone unit. As such, they are unique frustrated aromatic enes (FAEs). Various colored crystals of these FAEs, obtained in different solvents, correspond to multiple metastable conformations of the FAEs with various twist and fold angles of the C=C bond, as well as various dihedral angles of attached aryl units with respect to the C=C bond. The relationships between color and these parameters associated with conformational features around the C=C bond were elucidated in experimental and computational studies. Owing to the fact that they are separated by small energy barriers, the variously colored conformations in the FAE crystal change in response to various external stimuli, such as mechanical grinding, hydrostatic pressure and thermal heating.     

5β,6β‐Epoxy‐17‐oxoandrostan‐3β‐yl acetate and 5β,6β‐epoxy‐20‐oxopregnan‐3β‐yl acetate

In the title compounds, C₂₁H₃₀O₄, (I), and C₂₃H₃₄O₄, (II), respectively, which are valuable intermediates in the synthesis of important steroid derivatives, rings A and B are cis‐(5β,10β)‐fused. The two molecules have similar conformations of rings A, B and C. The presence of the 5β,6β‐epoxide group induces a significant twist of the steroid nucleus and a strong flattening of the B ring. The different C17 substituents result in different conformations for ring D. Cohesion of the molecular packing is achieved in both compounds only by weak intermolecular interactions. The geometries of the molecules in the crystalline environment are compared with those of the free molecules as given by ab initio Roothan Hartree–Fock calculations. We show in this work that quantum mechanical ab initio methods reproduce well the details of the conformation of these molecules, including a large twist of the steroid nucleus. The calculated twist values are comparable, but are larger than the observed values, indicating a possible small effect of the crystal packing on the twist angles.     

Anisotropy analysis of energy in Ag/Si twist interface

The energies in three combinations of Ag(001)/Si(111), Ag(011)/Si(111) and Ag(111)/Si(111) twist boundaries have been calculated using the modified embedded atom method (MEAM). The results show that the interface energies corresponding to Ag(111)/Si(111), Ag(001)/Si(111) and Ag(011)/Si(111) increase successively and the lowest energies 365, 717.7 and 996.1 mJ m^?2 corresponding to each interface appear at twist angles θ of 30, 0 and 25.24°, respectively. Considering minimization of interface energy, we can conclude that the Ag films deposited on Si(111) substrate will result in a (111) preferred orientation, especially at a twist angle of θ = 30°. Copyright © 2005 John Wiley & Sons, Ltd.     

Twisting of conjugated oligomers and polymers: case study of oligo- and polythiophene

Interring twisting (change in the dihedral angle between conjugated rings) of polythiophene was studied theoretically using periodic boundary conditions (PBC) at the B3LYP/6-31G(d) level. We find that the band gap of polymers is strongly dependent on the interring twist angle; yet twisting requires very little energy. A twist of 30 degrees increases the band gap by 0.75 eV in polythiophene, while requiring only 0.41 kcal mol(-1) per monomer unit. Such a small energetic value is of the order of crystal packing or van der Waals forces. These results are compared with calculations performed on model oligomers. Sexithiophene, its radical cations, and its dication are optimized at 0-180 degrees end-to-end twist angles (which correspond to 0-36 degrees interring dihedral angles) using the B3LYP/6-31G(d) method. The theoretical results suggest that the HOMO-LUMO gap, ionization potential, and charge distribution of oligomers are strongly dependent on twisting, whereas, similar to the case of polythiophene, twisting of neutral oligothiophenes costs very little energy. In the case of the radical cation, the lowest energy transition is shifted to a longer wavelength region on twisting, while the second-lowest energy transition is shifted to a shorter wavelength region. This implies that twisted, doped conducting polymers (modeled here by an oligomer radical cation), in contrast to planar, doped polymers, should be transparent within a certain optical window (in the far-visible region, at approximately 1.5 eV). This observation is explained on the basis of changes in the shape and overlap of the frontier molecular orbitals.     

Charge transport in self-organized pi-stacks of p-phenylene vinylene oligomers

We have studied the mobility of charge carriers along self-organizing pi-stacks of hydrogen-bonded phenylene vinylene oligomers in solution, by time-resolved microwave conductivity measurements. The value deduced for the mobility along the stacks is 3 x 10(-3) and 9 x 10(-3) cm2/(V s) for holes and electrons, respectively. Additionally, we have calculated the mobility along the pi-stacks using a hopping model based on parameters from density functional theory. The mobility values obtained from these calculations are in good agreement with the experimental values if it is assumed that there are relatively large twist angles between neighboring molecules in the stack. It is shown that a significantly higher mobility can be attained if the twist angle between neighboring oligomers is reduced.     

Periodic deformations induced by a magnetic field in planar twisted nematic layers

Magnetic field-induced spatially periodic deformations of planar nematic layers twisted by an angle Φ were investigated numerically. Chiral nematics with pitches compatible with the twist angle and non-chiral nematics twisted by Φ ? π/2 were considered. Two different modes of deformation, taking the form of stripes, were found: the so called Mode X, with periodicity parallel to the mid-plane director in the undisturbed structure, and Mode Y with periodicity perpendicular to the mid-plane director. The static director distributions were calculated for various magnetic field strengths, twist angles and elastic parameters. The influence of surface tilt was also investigated. Mode X appeared for sufficiently large Φ and was possible in nematics with typical elastic properties. Mode Y appeared provided that the k ₂₂/k ₁₁ elastic constant ratio and the twist angle Φ were sufficiently small. Both modes arose from the undistorted state when the magnetic field exceeded a threshold value. The spatial period of the patterns increased with field strength. At high field, regions with almost homogeneous deformation arose in the two halves of each stripe. Their width and, simultaneously, the spatial period diverged to infinity at some critical field. This divergence corresponds to the transition to a homogeneously deformed state. Diagrams were constructed showing the ranges of parameters favouring the periodic distortions.