Self-cleaning Hydrophobic Nanocoating on Glass: a Scalable Manufacturing Process

A method of forming a self-cleaning hydrophobic coating (SCHN) on glass substrates utilizing a scalable manufacturing process is described. The process initiates with roughening of planar glass surfaces using diamond micro-/nano-particle abrasives, which creates microscopic tortuous grooves. After cleaning the substrates, the roughened surface is vapor deposited with trichloro(1H,1H,2H,2H-perfluorooctyl)silane (TCPFOS) under enclosure with controlled humidity. TCPFOS chemically binds with the substrate via covalent linkage. Due to the greatly reduced surface tension between water and the self-cleaning surface, the water droplet slides down leaving no trail (sliding angle of 14° for 0.1 mL water droplet). Due to the reduced adhesion of dirt to the self-cleaning surface, the dirt particles are washed away by sliding or rolling water droplets. The SCHN shows no change in transmission as compared to the original glass substrate. The coating is resistant to multiple environmental factors including: abrasion cycles, acid rain (pH = 3), saline exposure (10% w/v), and extreme temperature cycling (-10 to 60 °C)

Electronic Structure and Vibrational Spectra of C2B10-Based Clusters and Films

The electronic structure, total energy, and vibrational properties of C2B10H12 (carborane)molecules and C2B10 clusters formed when the hydrogen atoms are removed from carborane molecules are studied using density functional methods and a semiempirical model. Computed vibrational spectra for carborane molecules are shown to be in close agreement with previously published measured spectra taken on carborane solids. Semiconducting boron carbide films are prepared by removing hydrogen from the three polytypes of C2B10H12 deposited on various surfaces. Results from x-ray and Raman scattering measurements on these films are reported. Eleven vibrationally stable structures for C2B10 clusters are described and their energies and highest occupied and lowest unoccupied molecular orbital gaps tabulated. Calculated Raman and infrared spectra are reported for the six lowest-energy clusters. Good agreement with the experimental Raman spectra is achieved from theoretical spectra computed using a Boltzmann distribution of the six lowest-energy free clusters. The agreement is further improved if the computed frequencies are scaled by a factor of 0.94, a descrepancy which could easily arise from comparing results of two different systems: zero-temperature free clusters and roomtemperature films. Calculated energies for removal of hydrogen pairs from carborane molecules are reported

Flexible Ag electrode for use in organic photovoltaics

High efficiency organic photovoltaic cells discussed in literature are normally restricted to devices fabricated on glass substrates. This is a consequence of the extreme brittleness and inflexibility of the commonly used transparent conductive oxide electrode, indium tin oxide (ITO). This shortcoming of ITO along with other concerns such as increasing scarcity of indium, migration of indium to organic layer, etc. makes it imperative to move away from ITO. Here we demonstrate a highly flexible Ag electrode that possesses low sheet resistances even in ultra-thin layers. It retains its conductivity under severe bending stresses where ITO fails completely. A P3HT:PCBM blend organic solar cell fabricated on this highly flexible electrode gives an efficiency of 2.3%

Enhancing current density using vertically oriented organic photovoltaics

We report a new organic photovoltaics (OPV) design, a wrapped OPV, which can circumvent both challenges of short exciton diffusion length [1], and low charge carrier mobility [2] of organic semiconductors by orienting the OPV vertically, to capture; manage; guide and use all incident photons and therefore, generate higher current. Resonant light, on being transmitted into a wrapped OPV, makes multiple passes through the photoactive layer and is absorbed completely, thus achieving benefits of thick photoactive layer while maintaining its ultra-thin thickness requirement. The current density generated from a wrapped OPV is twice than that generated by a similar OPV with flat orientation

Electrical transport measurements of highly conductive nitrogen-doped multiwalled carbon nanotubes/poly(bisphenol A carbonate) composites

Nitrogen-doped multiwalled carbon nanotubes with poly(bisphenol A carbonate) composites were prepared through simple solution blending. The scaling law, which is based on the percolation theory, is used to describe the electrical conductivities of the composites. Both direct current and alternating current conductivities are in good agreement with the unprecedented high saturated conductivities of the pristine samples (sat = -734 cm-1, pc = 0.19 wt%). We attributed the high conductivities to the binding of nanotubes into large but tight bundles, which enable the composites to carry more charges. This is notably different from the conventional method, which focuses on forming a well-dispersed three-dimensional network resulting in the conductivities having a lower order of magnitude. © Materials Research Society 2011

Stable organic photovoltaics using Ag thin film anodes

The interaction at the interface between a metal electrode and photoactive polymer is crucial for overall performance and stability of organic photovoltaics (OPVs). In this article, we report a comparative study of the stability of thin film Ag and indium tin oxide (ITO) as electrodes when used in conjunction with an interfacial PEDOT:PSS layer for P3HT:PCBM blend OPV devices. XPS measurements were taken for Ag and ITO/PEDOT:PSS layered samples with different exposure times to ambient conditions (∼25 °C, ∼50% relative humidity) to investigate the migration of Ag and In into the PEDOT:PSS layer. The change in efficiency of OPVs with a longer exposure time and degree of migration is explained by the analysis of XPS results. We propose the mechanism behind the interactions occurring at the interfaces. The efficiency of the ITO electrode OPVs continuously decreased to below 10% of the initial efficiency. However, the Ag devices displayed a slower degradation and maintained 50% of the initial efficiency for the same period of time

Spectroscopic studies of CSA-doped poly[C-hydroxyl-(4-N-dimethylamino)phenyl]dithienylmethine and doping effects on ionic conductivity

Protonation of poly[C-hydroxyl-(4-N-dimethylamino)phenyl]dithienylmethine with (1S)-(+)-10-camphorsulfonic acid (CSA) induced a structural change on the pendant group of the polymer and resulted in the formation of a cationic quinoid iminium moiety. This chemical transformation changed the polymer from a non-conducting polymer into a semi-conducting polymer with the maximum ionic conductivity of 2 × 10-4 S cm-1 at 10 mol% CSA-doping level. The polydithienylmethines doped with various CSA loadings were characterized by UV-vis-NIR, FT-IR and Raman spectroscopy. An ion-hopping mechanism was suggested as the conduction mechanism for this CSA-doped polymer. © 2006 Elsevier B.V. All rights reserved

Doping properties of polydithienylmethine: A study on the correlation between polymer chain length, spectroscopy, and transport

(1S)-(+)-10-Camphorsulfonic acid-doped polydithienylmethine was prepared through an acid-catalyzed condensation reaction of α,α′-di-2- thienyl-(2,2′-bithiophene)-5,5′-dimethanol and was characterized by 1H NMR spectroscopy and size exclusion chromatography (SEC). The electronic and vibrational properties of the resulting polymer thin films vary with the loadings of the (1S)-(+)-10-camphorsulfonic acid. The dark conductivity and drift mobility, which is significantly high, of the polymer thin films were enhanced with increasing doping levels and reached maximum values of 8.0 × 10-5 S·cm-1 and 3.5 × 10-2 cm2·V-1·s-1, respectively, at a 7 mol % dopant loading. Higher doping levels (\u3e7 mol %) result in nonuniform polymer thin films with degraded optical quality due to the formation of nanocrystalite and thus a decrease in conductivity and drift mobility was observed. The doped polydithienylmethine thin film also exhibited a photoconductivity response with an excitation at 457 nm and the highest photoconductivity (2 × 10-4 S·cm-1) was again observed at the 7 mol % doping level. Spectroscopic investigation suggests that the enhanced transport properties can be attributed to polaronic species present. The electronic and vibrational changes which relate to such doping were characterized by electronic absorption spectroscopy, Raman spectroscopy, and FTIR spectroscopy. The changes in transport values can be directly related to the changes we see in our spectroscopic investigations. © 2006 American Chemical Society

A resonance Raman study of carboxyl induced defects in single-walled carbon nanotubes

Changes in the vibrational response of single-walled carbon nanotubes (SWCNTs) resulting from the introduction of structural defects on their body were studied using resonance Raman spectroscopy. Structural defects were introduced on the SWCNTs by subjecting them to carboxylation for different intervals of time. Various Raman modes were observed, including the D, G/G -, G\u27 modes, and new defect induced modes were identified. Weaker vibrational modes corresponding to StoneWales defects with specific structures known as Haeckelites were identified. These modes were compared with the theoretically calculated modes and correlated to O5,6,7 and R 5,7 Haeckelite structures. © 2010 Elsevier B.V. All rights reserved