Rate-determining process in MISIM photocells for optoelectronic conversion using photo-induced pure polarization current without carrier transfer across interfaces

Recently, we proposed a [metal|insulator|semiconductor|insulator|metal] (MISIM) photocell, as a novel architecture for high-speed organic photodetectors. The electric polarization in the S layer, induced by modulated light illumination, propagates into the outside circuit as a polarization current through the I layers, without any carrier transfer across the interfaces. In the present work, we examined the MISIM photocells consisting of zinc-phthalocyanine(ZnPc)-C60 bilayers for the S layer and Parylene C for the two I layers, to understand the fundamental aspects of the MISIM photocells, such as current polarity and modulation-frequency dependence. It was found that, in such devices, the current polarity was primarily determined by the polarization in the S layer, which was induced by the donor–acceptor charge-transfer upon illumination. Furthermore, the ON and OFF current, which appeared in the periods of illumination-on and -off, respectively, exhibited significantly different dependence on the modulation frequency. This was well-explained by an imbalance between a quick polarization in the S layer during illumination and its slow relaxation in the dark

Fluorination induced electronic effects on Pt(II) square-planar complex of o-phenylenediimine ligand

A novel complex [Pt(C6F4(NH)2)2] (2), formed by a Pt(ii) cation bound to two molecules of the tetrafluorinated 1,2-phenylenediimine ligand, has been synthesized and characterized by electrochemical and XRD measurements, UV-vis-NIR spectroscopy as well as by DFT and TD-DFT calculations. The effect induced by the fluorine atoms has been highlighted by comparison with the corresponding Ni (1H) and Pt (2H) hydrogenated complexes. The cyclic voltammetry data show that the reduction and the oxidation processes of 2 are easier and more difficult (by about 0.5 V), respectively, compared to those of 1H and 2H, suggesting that the electron withdrawing ability of the fluorine atoms lowers the energy level of both the HOMO and the LUMO. UV-vis-NIR measurements are similar for all the three complexes, indicating similar HOMO-LUMO gaps and that the effects of fluorination on the frontier orbitals are roughly the same. Moreover, polymorphism in the powder form of 2 has been highlighted by XRD measurements while the film presents only one phase. Furthermore, this complex shows a field-effect for n-type carriers. All the experimental results are also supported by the calculations, which show the role played by the fluorine atoms in the electronic structure of 2

Electrochemical deposition of highly-conducting metal dithiolene films

Electrochemical deposition has been used to prepare a thin film of neutral 4′,4-(3-alkyl)-thiophene-5′,5-hydogen-nickel and copper dithiolenes (Ni–C2, Cu–C2).</p

Single-component reflecting objective for low-temperature spectroscopy in the entire visible region

A single-component reflecting objective was constructed for low-temperature spectroscopy with optimal imaging and transmission properties at all visible wavelengths. The performance of the objective immersed in superfluid helium at a temperature of 1.5 K was tested by comparing dark-field images of uncolored polymer beads taken at wavelengths of 400 and 800 nm. Under conditions optimized for imaging at both wavelengths, the size of the image i

Noticias

The <i>K</i>₄ structure was theoretically predicted for trivalent chemical species, such as sp² carbon. However, since attempts to synthesize the <i>K</i>₄ carbon have not succeeded, this allotrope has been regarded as a crystal form that might not exist in nature. In the present work, we carried out electrochemical crystallization of the radical anion salts of a triangular molecule, naphthalene diimide (NDI)-Δ, using various electrolytes. X-ray crystal analysis of the obtained crystals revealed the <i>K</i>₄ structure, which was formed by the unique intermolecular π overlap directed toward three directions from the triangular-shape NDI-Δ radical anions. Electron paramagnetic resonance and static magnetic measurements confirmed the radical anion state of NDI-Δ and indicated an antiferromagnetic intermolecular interaction with the Weiss constant of θ = −10 K. The band structure calculation suggested characteristic features of the present material, such as a metallic ground state, Dirac cones, and flat bands

Giant negative magnetoresistance in Ni(quinoline-8-selenoate) 2

Authors thank the University of St Andrews, the Leverhulme Trust (International Network Grant IN-2012-094) and the JSPS Core-to Core Program, A. Advanced Research Networks for support.The magnetic, structural, conductivity and magnetoresistance properties of [Ni(quinoline-8-selenoate)2] ([Ni(qs)2]) have been studied. Despite the insolubility of the material necessitating its study as a powdered sample, a remarkably high conductivity has been measured. The conductivity is an order of magnitude greater than the thin-film processable thiol analogue previously reported and has been interpreted through the same space-charge limited conduction mechanism with charges injected from the electrodes. The introduction of selenium, results in a material with conductivity approaching metallic due to the enhanced interaction between adjacent molecules. Additionally, under an applied magnetic field, the material displays a negative magnetoresistance effect above 35% at 2 K. The effect can still be observed at 200 K and is interpreted in terms of a double-exchange mechanism.Publisher PDFPeer reviewe

Molecular and thin film properties of cobalt half-sandwich compounds for optoelectronic application

The structure and electronic properties of a novel cobalt half sandwich complex of cyclopentadiene (Cp) and diaminonaphthalene (DAnap) [CpCo(DAnap)] are described and compared to the previously reported diaminobenzene derivative [CpCo(DAbnz)] in view of their potential for (opto)electronic device application. Both complexes show stable redox processes, tunable through the diaminoacene ligand, and show strong absorption in the visible region, with additional transitions stretching into the near infrared (NIR). CpCo(DAnap) crystallises with a particularly large unit cell (9301 Å3), comprising 32 molecules, with a gradual rotation over 8 molecules along the long c-axis. In the solid state the balance of the optical transitions in both complexes is reversed, with a suppression of the visible band and an enhancement of the NIR band, attributed to extensive intermolecular electronic interaction. In the case of CpCo(DAnap), highly crystalline thin films could be formed under physical vapor deposition, which show a photocurrent response stretching into the NIR, and p-type semiconductor behavior in field effect transistors with mobility values of the order 1 × 10−4 cm2 V−1 s−1. The device performance is understood through investigation of the morphology of the grown films