Photo stability enhancement of Poly(3-hexylthiophene)-PCBM nanocomposites by addition of multi walled carbon nanotubes under ambient conditions

Poly(3-hexylthiophene)-Phenyl-C61-butyric acid methyl ester (P3HT–PCBM) composites find wide application in optoelectronic devices, especially bulk-hetero junction (BHJ) solar cells. These composites, even though could give efficient polymer solar cells with ∼4–5% power conversion efficiencies (PCE), a major problem of photo stability is associated with it and remains unsolved. P3HT–PCBM composite was found to be degrading on irradiation with ultraviolet radiation or a solar simulator providing AM1.5G illumination (1000 W m^–2, 72 ± 2 °C or 330 W m⁻², 25 °C), in presence of oxygen and moisture. Here, we have studied the photo stability of P3HT–PCBM under ambient conditions and showed that a new ternary composite, P3HT–PCBM–MWCNT (multi walled carbon nanotube) has superior photo stability even on extended UV–Vis exposure. A total of 7% (w/w) PCBM and 3% (w/w) MWCNT with respect to P3HT resulted in optimum stability. UV–Visible and fluorescence spectral analysis have been used to study the photo stability, both in solution state and solid/film state. Transmission electron micrograph (TEM) along with selected area electron diffraction (SAED) pattern and Field Emission Scanning Electron Microscopy (FE-SEM) micrographs have been used to show the well coating of MWCNT on P3HT–PCBM composite. Since MWCNT is one of the very important carbon based nanomaterial with several supreme characteristics, this new ternary composite has great importance for optoelectronic applications.     

Switch the n-type to ambipolar transfer characteristics by illumination in n-type pentacene-based organic field-effect transistors

This work investigates the suppression of n-channel and the switch of transfer characteristics (from n-type to ambipolar) by illumination in n-type pentacene-based organic field-effect transistors (OFETs). The illumination outcomes differently on the output characteristics of OFETs, which markedly decreases the magnitude of drain current (n-channel) and shifts the turn-on voltage to a higher positive bias in the n-type regime, but induces the formation of p-channel in the p-type regime. We attribute that the trapped negative charges in the device as induced by illumination electrostatically shield the effective electrical field applied to the gate with source/drain electrodes and modulate the device performance. The result of quasi-static capacitance–voltage measurement agrees well with the modulations of the transfer characteristics for n-type OFETs by illumination. In addition, the de-trapping of charges recovers the n-type only output characteristics of pentacene-based OFETs. This study highlights the unique photo responses of n-type pentacene-based OFETs to the development of phototransistors of distinct output characteristics operated in n- and p-type regime.     

随机介质中的相干背散射

相干背散射是由于随机介质中的多次散射而导致的一种自相干效应。通过多年的探索,人们在实验和理论研究方面取得了一系列激动人心的进展。本文介绍了相干背散射的基本原理和实验方法,总结了当前的研究进展。     

Effective temperature of thermal radiation from non-uniform temperature distributions and nanoparticles

We study thermal radiation properties from non-uniform temperature distributions and nanoparticles, and define effective temperature. Conventionally, the temperature of a body is measured by fitting with the blackbody radiation spectrum, which assumes a uniform temperature throughout the body. We show the energy density of thermal radiation for non-uniform temperature distribution of the body and derive the effective temperature. Furthermore, the energy density of thermal radiation from nanoparticles is derived and the effective temperature of the body is shown to depend on the particle size.     

Classical aspects emerging from local control of energy and particle transfer in molecules

The question in how far classical mechanics can be used to describe coherent control processes in molecules is addressed within the framework of local control theory. Therefore, quantum and classical calculations are compared for a model proton transfer process and also for the multi-photon infrared dissociation of the HOD molecule. It is shown that control fields can be derived classically as long as wave packet dispersion is not too large. This hints at further applications which might be helpful to devise control fields for complex molecular systems being present in biological processes.     

Continuum generation in water and carbon tetrachloride using a picosecond Nd-YAG laser pulse

We have measured the continuum generated in two non-linear media, distilled water and carbon tetrachloride, pumped by a 36 ps Neodymium Yttrium Aluminium Garnet laser pulse operating at 1.06 μm. We show that the induced spectral broadening extends from 400 nm to 850 nm in both media. However, we find that continuum spectra of carbon tetrachloride exhibit an oscillatory structure with an energy range of about 445 cm⁻¹ which corresponds to the fundamental Raman component. This behaviour is due to a spectral non-overlapping of the Raman anti-Stokes components photoinduced in this medium.     

Carrier mobility of photochromic diarylethene amorphous films

Photochromic diarylethenes (DAEs) have gained attention as attractive current switching materials by light irradiation in the organic electronics field. We investigated the hole mobility of amorphous films consisting of three types of DAEs using a space-charge-limited current method and a better chemical structure to achieve high mobility. The hole mobility of open-ring (colorless) DAE having benzothiophene rings substituted with triphenylamine (TPA) as an aryl group was 2 × 10⁴ times (2 × 10⁻⁶ cm²/V s) larger than that of DAE containing thiophene rings without TPA. When the DAE film was irradiated with ultraviolet (UV) light, the hole mobility decreased temporarily at 4% of closed-ring (colored) isomers and then increased to two-three times of the initial colorless state at 85% of the closed-ring isomers. The temporary decrease in the hole mobility originated in the hole trapping effect of the closed-ring molecules in a matrix consisting of open-ring isomers.     

Surface Modifications and Optoelectronic Characterization of TiO2‐Nanoparticles: Design of New Photo‐Electronic Materials

TiO₂ nanoparticles are of great current interest for applications in photo‐electronic materials including light‐energy conversion, artificial photosynthetic systems as well as photocatalysis. The success of these applications relies on the exciton recombination dynamics and visible‐light sensitivity of the TiO₂ nanomaterials. Thus, in order to develop the highly efficient photo‐electronic materials absorbing visible light, different low dimensional TiO₂ nanostructures such as nanodiscs, nanofibers and nanochains were synthesized, and thereafter their surfaces were modified by incorporating with Sn‐porphyrins and heteropoly acid. The optoelectronic properties of the surface‐modified nanomaterials were investigated with regard to the optical properties and the surface exciton dynamics by using both steady‐state and ultrafast time‐resolved laser spectroscopic techniques including single nanoparticle photoluminescence technique. These results were correlated with the photo‐electronic properties including photocatalytic activities and solar cell efficiencies, indicating that the electron transfer mechanism in the modified nanostructures may be similar to the “Z‐scheme” of the plant photosynthetic system so that both photocatalytic activity and solar cell efficiencies were synergistically enhanced by using two color illumination.     

A review of optical measurements at the aerosol and cloud chamber AIDA

This paper provides a survey of recent studies on the optical properties of aerosol and cloud particles that have been conducted at the AIDA facility of Forschungszentrum Karlsruhe (Aerosol Interactions and Dynamics in the Atmosphere). Reflecting the broad accessible temperature range of the AIDA chamber which extends from ambient temperature down to 183 K, the investigations feature a broad diversity of research topics, such as the wavelength-dependence of the specific absorption cross sections of soot and mineral dust aerosols at room temperature, depolarization and infrared extinction measurements of ice crystal clouds generated at temperatures below 235 K, and the optical properties of polar stratospheric cloud constituents whose formation was studied in chamber experiments at temperatures well below 200 K. After reviewing the AIDA research activity of the past decade and introducing the optical instrumentation of the AIDA facility, this paper presents illustrative examples of ongoing and already published work on optical measurements of soot aerosols, mineral dust particles, and ice crystal clouds.     

Charge storage and electron/light emission properties of silicon nanocrystals

Monodispersed silicon nanocrystals show novel electrical and optical characteristics of silicon quantum dots, such as single-electron tunneling, ballistic electron transport, visible photoluminescence and high-efficiency electron emission.Single-electron memory effects have been studied using a short-channel MOSFET incorporating Si quantum dots as a floating gate. Surface nitridation of Si nanocrystal memory nodes extends the charge-retention time significantly. Single-electron storage in individual Si dots has been evaluated by Kelvin probe force microscopy.Photoluminescence and electron emission are observed for surface-oxidized silicon nanocrystals. Efficiency of the no-phonon-assisted transition increases with decreasing core Si size. Electron emission efficiency as high as 5% has been achieved for the Si-nanocrystal-based cold electron emitter devices. The non-Maxwellian energy distribution of emitted electrons suggests that the mechanism of electron emission is due to ballistic transport through arrays of surface-oxidized Si nanocrystals. Combined with the ballistic electron emission, the quasi-direct light emission properties can be used for developing Si-based lasers.