Modification in cell structure for better performance of spray pyrolysed CuInS2/In2S3 thin film solar cell

We report a new structure for CuInS₂/In₂S₃ solar cell, in which both absorber and buffer layers were deposited using chemical spray pyrolysis (CSP) technique. The usual superstrate structure, having buffer layer just above ITO, was not functioning mainly due to diffusion of Cu into In₂S₃ layer as seen from X-ray photoelectron spectroscopy (XPS) results. However, when the configuration of the cell was ITO/CuInS₂/In₂S₃/Ag, cell parameters obtained were V_oc=0.45 V, J_sc=44.03 mA/cm², fill factor (FF) = 29.5% and η=5.87%. Good results could be obtained by using indium sulfide thin films having maximum photosensitivity. The cell was characterized using X-ray diffraction, optical absorption, current–voltage and spectral response measurements. PACS 81.15.Rs; 82.45.Mp; 84.60.Jt     

Crystal and molecular structure of 1-(p-bromobenzoyl)-2-methyl-1,2,3,4-tetrahydroquinoline

Crystals of the title compound, C₁₇H₁₆BrNO, are monoclinic, space groupP2₁/n, unit-cell parametersa = 14.48,b = 6.20,c = 16.72 Å, and = 97.35 °. Three-dimensional data were collected with CuK radiation using an automatic diffractometer. The structure was solved by the heavy-atom method and refined by block diagonal least squares to anR index of 0.088 for 2210 reflections. The main features obtained from our studies are (i) the C=O group is orientedanti to the benzene ring, in agreement with the nmr studies; (ii) the C(2) proton is equatorial while the methyl group at C(2) is in an axial position, also in agreement with nmr data. The bromobenzoyl ring and the benzene ring are at 64 ° to each other, while the carbonyl >C=O and the bromobenzoyl groupsBr are at 42 ° to each other.     

Preparation, structural analysis and dielectric properties of Bi x La1−x FeO3 perovskite

Rare earth element substituted bismuth ferrites (BiFeO₃) are of enormous importance as magnetoelectric materials. The polycrystalline samples of Bi _x La_1−x FeO₃ (x=0, 0.2, 0.4, 0.6, 0.8) were prepared by solid-state reaction using standard ceramic method. The single-phase formation of these compounds was confirmed by X-ray diffraction (XRD) studies. The samples with x=0, 0.2, 0.4, 0.6 are found to be orthorhombic while the sample with x=0.8 is triclinic. The dielectric constant (ε′) and dissipation factor (tan δ) were measured in the frequency range 100 Hz to 1 MHz at room temperature and as a function of temperature at certain fixed frequencies (1 kHz, 10 kHz, 100 kHz, 1 MHz). All the samples showed dielectric dispersion. The dielectric constant with temperature shows a broad peak; the peak temperature shifts with frequency which reflects the relaxor-type behavior. The peak above 600 K in the measured temperature range corresponds to antiferromagnetic ordering temperature (Néel temperature). The broadness of the peak changes with composition. The ac conductivity as well as ε′ are found to be maximum for the sample x=0.2 at room temperature.     

Magnetoelectric effect in cobalt ferrite-barium titanate composites and their electrical properties

CoFe₂O₄-BaTiO₃ composites were prepared using conventional ceramic double sintering process with various compositions. Presence of two phases in the composites was confirmed using X-ray diffraction. The dc resistivity and thermoemf as a function of temperature in the temperature range 300 K to 600 K were measured. Variation of dielectric constant (ɛ′) with frequency in the range 100 Hz to 1 MHz and also with temperature at a fixed frequency of 1 kHz was studied. The ac conductivity was derived from dielectric constant (ɛ′) and loss tangent (tan δ). The nature of conduction is discussed on the basis of small polaron hopping model. The static value of magnetoelectric conversion factor has been studied as a function of magnetic field.     

Vibrational spectra and normal coordinate analysis of dihalogenated benzenes. II. Out-of-plane vibrations

Assignments of the out-of-plane fundamental modes for D₄-ortho, meta and para fluorochloro and fluorobromo benzenes are given. A normal coordinate analysis, employing the 94 observed frequencies of the H₄ and D₄ molecules is carried out to obtain a 16-parameter Valence Force Feld, with an average difference of ±1.2% between observed and calculated frequencies. Unique assignments are obtained in the spectra of D₄-compounds for several of the weak or overlapping bands assigned as fundamentals in the H₄-compounds.     

On the dipole moments and first-order hyperpolarizability of N,N-bis(4-bromobutyl)-4-nitrobenzenamine

The nonlinear optical molecule N,N-bis(4-bromobutyl)-4-nitrobenzenamine was synthesized. The ground state dipole moment was determined by the Debye-Guggenheim method. A solvent mixture of acetonitrile and toluene was used for the solvatochromic determination of the excited state dipole moment. Excited state has a high value for the dipole moment which indicated a higher degree of charge transfer from the donor to the acceptor moiety on excitation by light. The first hyperpolarizability (beta(ijk)) of the molecule was evaluated assuming the two level model of the first hyperpolarizability.     

An investigation on the variations in properties of Ni+ irradiated ZnO thin films

ZnO thin films, irradiated by 80 MeV Ni⁺ ions, were analysed with the help of different characterization techniques like X-ray diffraction, optical absorption, transmission, photoluminescence (PL), electrical resistivity, photosensitivity (PS) and thermally stimulated current (TSC) measurements. Crystallinity and absorption edge were hardly affected by irradiation. PL spectrum of pristine sample showed a broad peak at 517 nm, whereas irradiated film had two emissions at 517 and 590 nm. Intensity ratio between these two emissions (I₅₁₇/I₅₉₀) decreased with the fluence, and finally at a fluence of 3×10¹³ ions/cm², the emission at 517 nm completely disappeared. Electrical resistivity of the sample irradiated with a fluence of 1×10¹³ ions/cm² drastically increased. However, on increasing the fluence to 3×10¹³ ions/cm², resistivity decreased, probably due the onset of hopping conduction through defects. PS also decreased due to irradiation. TSC measurements on pristine sample could reveal only one defect level at 0.6 eV, due to interstitia1 zinc (Zn_I). But, irradiation at a fluence of 1×10¹² ions/cm², resulted in three different defect levels as per TSC studies. Interestingly, the sample irradiated at a fluence of 3×10¹³ ions/cm² had only one defect level corresponding to a deep donor. The possible origin of these defect levels is also discussed in the paper.     

Excitation energy migration in oligo(p-phenylenevinylene) based organogels: structure-property relationship and FRET efficiency

Excitation energy migration (EM) and assisted energy transfer (ET) properties of a few oligo(p-phenylenevinylene) (OPV) based organogelators with different end functional groups have been studied using picosecond time-resolved emission spectroscopy (TRES). EM was found to be more efficient in OPV gelators with small end functional groups (OPV3-4) when compared to that of the gelators with bulky end groups (OPV1-2) in the gel state. TRES studies at elevated temperature and in chloroform solution highlight the role of the self-assembled scaffolds in assisting the EM and ET processes. Increase in temperature and solvent polarity leads to the aggregate breaking and hence adversely affects the EM and ET efficiencies. The effect of EM efficiency on the fluorescence resonance energy transfer (FRET) properties of the OPV gels was studied by using OPV1 and OPV3 as the donors and OPV5 as the acceptor. Better transfer of excitation energy was observed in the donor system (OPV3) having higher EM efficiency even at very low concentration (3.1 mol%) of the acceptor molecules, whereas ET efficiency was lower in the donor system (OPV1) with low EM efficiency.     

Interplay between H‐Bonding and Preorganization in the Evolution of Self‐Assembled Systems

Cooperative π–π interactions and H‐bonding are frequently exploited in supramolecular polymerization; however, close scrutiny of their mutual interplay has been largely unexplored. Herein, we compare the self‐assembly behavior of a series of C₂‐ and C₃‐symmetrical oligophenyleneethynylenes differing in their amide topology (N‐ or C‐centered). This subtle structural modification brings about drastic changes in their photophysical and supramolecular properties, highlighting the reciprocal impact of H‐bonding vs. preorganization on the evolution and final outcome of supramolecular systems.