Volume 6, Issue 12, December 2013
Index of content:
- ORGANIC ELECTRONICS AND PHOTONICS
Improving the performance of organic thin film transistors formed on a vacuum flash-evaporated acrylate insulator103(2013); http://dx.doi.org/10.1063/1.4839275View Description Hide Description
A systematic investigation has been undertaken, in which thin polymer buffer layers with different ester content have been spin-coated onto a flash-evaporated, cross-linked diacrylate gate-insulator to form bottom-gate, top-contact organic thin-film transistors. The highest device mobilities, ∼0.65 cm2/V s and ∼1.00 cm2/V s for pentacene and dinaphtho[2,3-b:2′,3′-f]-thieno[3,2-b]thiophene (DNTT), respectively, were only observed for a combination of large-grain (∼1–2 μm) semiconductor morphology coupled with a non-polar dielectric surface. No correlation was found between semiconductor grain size and dielectric surface chemistry. The threshold voltage of pentacene devices shifted from −10 V to −25 V with decreasing surface ester content, but remained close to 0 V for DNTT.
Barrier performance optimization of atomic layer deposited diffusion barriers for organic light emitting diodes using x-ray reflectivity investigations103(2013); http://dx.doi.org/10.1063/1.4839455View Description Hide Description
The importance of O3 pulse duration for encapsulation of organic light emitting diodes (OLEDs) with ultra thin inorganic atomic layer deposited Al 2O3 layers is demonstrated for deposition temperatures of 50 °C. X-ray reflectivity (XRR) measurements show that O3 pulse durations longer than 15 s produce dense and thin Al 2O3 layers. Correspondingly, black spot growth is not observed in OLEDs encapsulated with such layers during 91 days of aging under ambient conditions. This implies that XRR can be used as a tool for process optimization of OLED encapsulation layers leading to devices with long lifetimes.
Performance improvement of inverted polymer solar cells by doping Au nanoparticles into TiO2 cathode buffer layer103(2013); http://dx.doi.org/10.1063/1.4840319View Description Hide Description
Gold nanoparticles (Au NPs) were synthesized by a facile method. Then Au NPs with different sizes and weight ratios were blended into the TiO2 cathode buffer layer of the polymer solar cells (PSCs) with a blend of poly (3-hexylthiophene) (P3HT) and [6,6]-phenyl-C61-butyric acid methyl ester (PCBM) as the active layer. The light absorption of the devices was enhanced by incorporating Au NPs into the Bulk heterojunction (BHJ) polymer solar cells, which support localized surface plasmon resonance (LSPR). The results showed that the short-circuit current density (JSC) was apparently enhanced by doping Au NPs into the buffer layer while maintaining the open-circuit voltage (VOC) and fill factor(FF), leading to an increase in power conversion efficiency.
Solution-based silk fibroin dielectric in n-type C60 organic field-effect transistors: Mobility enhancement by the pentacene interlayer103(2013); http://dx.doi.org/10.1063/1.4841595View Description Hide Description
A pentacene interlayer of 2 nm thick is inserted between fullerene (C60) and the solution-based silk fibroin dielectric in C60 organic field-effect transistors (OFETs). The pentacene interlayer assists to improve crystal quality of the C60 layer, leading to the increase of field-effect mobility (μ FE) from 0.014 to 1 cm2 V−1 s−1 in vacuum. The μ FE value of the C60 OFET is further enhanced to 10 cm2 V−1 s−1 when the OFET is exposed to air in a relative humidity of 55%. Generation of mobile and immobile charged ions in solution-based silk fibroin in air ambient is proposed.
103(2013); http://dx.doi.org/10.1063/1.4840335View Description Hide Description
Electric field activated nonlinear transport is investigated in polypyrrole thin film in both in-plane and out-of-plane geometries down to 5 K and strong anisotropy is observed. A morphological model is suggested to explain the anisotropy through inter-chain and intra-chain transport. The deviation from the variable range hopping at low temperature is accounted by fluctuation assisted transport. From Zabrodaskii plots, it is found that electric field can tune the transport from insulating to metallic regime. Glazman–Matveev model is used to describe the nonlinear conduction. Field scaling analysis shows that conductance data at different temperature falls on to a single curve. Nonlinearity exponent, mT and characteristic length, LE are estimated to characterize the transport in both the geometries.