Calculating optical absorption spectra of thin polycrystalline films: Structural disorder and site-dependent van der Waals interaction

We propose a new approach for calculating the change of the absorption spectrum of a molecule when moved from the gas phase to a crystalline morphology. The so-called gas-to-crystal shift $\Delta{\cal E}_m$ is mainly caused by dispersion effects and depends sensitively on the molecule's specific position in the nanoscopic setting. Using an extended dipole approximation, we are able to divide $\Delta{\cal E}_m= -Q W_{m}$ in two factors where $Q$ depends only on the molecular species and accounts for all non-resonant electronic transitions contributing to the dispersion, while $W_m$ is a sum running over the position of all molecules expressing the site-dependence of the shift in a given molecular structure. The ability of our approach to predict absorption spectra is demonstrated using the example of polycrystalline films of 3,4,9,10-perylene-tetracarboxylic-diimide (PTCDI).Comment: 6 pages, 4 figure

Low-voltage organic transistors and inverters with ultra-thin fluoropolymer gate dielectric

We report on the simple fabrication of hysteresis-free and electrically stable organic field-effect transistors (OFETs) and inverters operating at voltages <1-2 V, enabled by the almost trap-free interface between the organic semiconductor and an ultra-thin (<20 nm) and highly insulating single-layer fluoropolymer gate dielectric (Cytop). OFETs with PTCDI-C13 (N,N'-ditridecylperylene-3,4,9,10-tetracarboxylicdiimide) as semiconductor exhibit outstanding transistor characteristics: very low threshold voltage (0.2V), onset at 0V, steep subthreshold swing (0.1-0.2 V/decade), no hysteresis and excellent stability against gate bias stress. It is gratifying to notice that such small OFET operating voltages can be achieved with the relatively simple processing techniques employed in this study.Comment: Accepted for publication in Applied Physics Letter

Effects of pore modification on the templating of guest molecules in a 2D honeycomb network

This work was supported by the UK Engineering Physical Sciences Research Council (EPRSC) and the EU.1,7-Diadamantanethioperylene-3,4:9,10-tetracarboxylic diimide, (Ad-S)(2)-PTCDI, adsorbed on Au (111) from solution was investigated by scanning tunneling microscopy (STM) and X-ray photoelectron spectroscopy (XPS). (Ad-S)(2)-PTCDI forms a well-ordered monolayer whose structure is described by a (2 root 63 x root 19) R19.1 degrees chiral unit cell containing four molecules. Codeposition of (Ad-S)(2)-PTCDI with 1,3,5-triazine-2,4,6-triamine (melamine) yields a honeycomb network whose (7 root 3 x 7 root 3)R30 degrees unit cell is identical to the unsubstituted PTCDI/melamine analogue. The effect of the adamantyl thioether moieties on the adsorption of guest molecules is investigated using adamantane thiol and C-60. While the thioether units do not affect the packing of adamantane thiol molecules a pronounced influence is seen in the case of fullerene. Pore modification involving different combinations of enantiomers of (Ad-S)(2)-PTCDI give rise to distinctly different arrangements of C-60 molecules. The diversity of patterns is further increased by the presence of unsubstituted PTCDI molecules.PostprintPeer reviewe

N,N'-dimethylperylene-3,4,9,10-bis(dicarboximide) on alkali halide(001) surfaces

The growth of N,N'-dimethylperylene-3,4,9,10-bis(dicarboximide) (DiMe-PTCDI) on KBr(001) and NaCl(001) surfaces has been studied. Experimental results have been achieved using frequency modulation atomic force microscopy at room temperature under ultra-high vacuum conditions. On both substrates, DiMe-PTCDI forms molecular wires with a width of 10 nm, typically, and a length of up to 600 nm at low coverages. All wires grow along the [110] direction (or [1$\bar{1}$0] direction, respectively) of the alkali halide (001) substrates. There is no wetting layer of molecules: Atomic resolution of the substrates can be achieved between the wires. The wires are mobile on KBr surface but substantially more stable on NaCl. A p(2 x 2) superstructure in brickwall arrangement on the ionic crystal surfaces is proposed based on electrostatic considerations. Calculations and Monte-Carlo simulations using empirical potentials reveal possible growth mechanisms for molecules within the first layer for both substrates, also showing a significantly higher binding energy for NaCl(001). For KBr, the p(2 x 2) superstructure is confirmed by the simulations, for NaCl, a less dense, incommensurate superstructure is predicted.Comment: 5 pages, 5 figure

Fabrication of Photovoltaic Cell From Rhenium Containing Polymer

Photovoltaic devices were fabricated using rhenium bis(arylimino) acenaphthene (DIAN) complex containing poly(p-phenylenevinylene). These polymers absorb strongly in the visible region at ca. 440-550 nm. In addition, this type of transition metal based polymers have been shown to exhibit large photo-sensitivity due to the presence of the rhenium complex, which has a relatively long-lived Metal-to-Ligand Charge Transfer (MLCT) character. By using this type of polymers, the metal content can be adjusted easily by simply changing the monomer feed ratio. Moreover, the excited state properties and electronic absorption properties can be modified by varying the structure of the diimine ligand coordinated to the metal. This approach allows us to fine-tune the absorption spectra of the polymers by employing different types of rhenium complex derivatives. PEDOT:PSS and PTCDI were used as the hole and electron transport layers, respectively. The ITO/PEDOT:PSS/DIAN-PPV/PTCDI/Al devices were found to exhibit photovoltaic response under the illumination of AMI solar radiation. The short-circuit current ISC, open-circuit voltage V OC, and the fill factor FF were measured to be 38 μA/cm 2, 0.93 V and 0.21 respectively. Another photovoltaic device was prepared with the structure ITO/PEDOT:PSS/DIAN-PPV:TiO2/PTCDI/Al and its photovoltaic properties were studied. The presence of TiO2 will assist the electron transport of the DIAN-PPV to the PTCDI, in which the electrons can be collected at the aluminium electrode. The short-circuit current ISC open-circuit voltage VOC, and the fill factor FF were measured to be 51 μA/cm2, 1.18 V and 0.12 respectively. It was observed that the power conversion efficiency of photovoltaic devices related closely to the rhenium content and the structure of the rhenium complex used.published_or_final_versio

Influence of the device architecture to the ITO surface treatment effects on organic solar cell performance

In this work, we investigate the influence of different indium tin oxide (ITO) surface treatments on the performance of organic solar cells with different device architectures. Two layer cells with different layer hierarchy (ITO/copper phthalocyanine (CuPc)/fullereve (C60/Al and ITO/C 60/CuPc/Cu) and three layer cells with mixed layer inserted between CuPc and C60 were fabricated. We found that in all cases the short circuit current was the parameter which was most significantly affected by ITO surface treatment. However, the performance of the cells with C60 layer in contact with ITO was markedly less sensitive to the ITO surface treatments compared to the cells with CuPc in contact with ITO. The cells with C60 layer in contact with ITO also exhibited higher efficiency compared to the cells with CuPc in contact with ITO. We also fabricated two layer cells with structures ITO/CuPc/perylene tetracarboxylic acid diimide (PTCDI)/Al and ITO/PTCDI/CuPc/Cu. In this case, we also obtain higher efficiency and lower sensitivity to ITO properties when "n type" material is in contact with ITO. The best obtained AMI power conversion efficiency was 0.4% for ITO/PTCDI/CuPc/Cu cell and ITO/C60/CuPc:C60/CuPc/Cu cells.published_or_final_versio

Length-Independent Charge Transport in Chimeric Molecular Wires

Advanced molecular electronic components remain vital for the next generation of miniaturized integrated circuits. Thus, much research effort has been devoted to the discovery of lossless molecular wires, for which the charge transport rate or conductivity is not attenuated with length in the tunneling regime. Herein, we report the synthesis and electrochemical interrogation of DNA-like molecular wires. We determine that the rate of electron transfer through these constructs is independent of their length and propose a plausible mechanism to explain our findings. The reported approach holds relevance for the development of high-performance molecular electronic components and the fundamental study of charge transport phenomena in organic semiconductors

Growth of molecular superlattice and its physical and device properties at heteromolecular interface

筑波大学University of Tsukuba博士（工学）Doctor of Philosophy in Engineering2010【要旨】thesi

Studies of molecular beams of organic materials

Tato bakalářská práce se zabývá sestavením nízkoteplotní efuzní cely vhodné pro napařování organických materiálů. Je provedena kalibrace provozních teplot efuzní cely. Jsou provedeny depozice organického polovodičového materiálu a je proměřena morfologie povrchu vzniklých vrstev na AFM a SEM zařízení. Součástí práce je rešeršní studie shrnující poznatky o využití organických materiálů v polovodičovém průmyslu.This bachelor's thesis deals with assembling of low-temperature efussion cell which is suitable for deposition of organic materials. The calibration of operating temperature of effusion cell is performed. Depositions of organic semiconductor material are realized. Morphology of surface of thin film is studied in AFM and SEM microscope. In the paper background research on the utilization of organic materials in semiconductor industry is presented.

The role of “disaggregation” in optical probe development

10.1039/c3cs60368gChemical Society Reviews4382402-241