Synthesis, characterization and organic field effect transistor performance of a diketopyrrolopyrrole-fluorenone copolymer

A diketopyrrolopyrrole (DPP) with fluorenone (FN) based low band gap alternating copolymer (PDPPT-alt-FN) has been synthesized via Suzuki coupling. PDPPT-alt-FN exhibits a deep HOMO level with a lower band gap. Fabricated organic thin film transistors using PDPPT-alt-FN as a channel semiconductor show p-channel behaviour with the highest hole mobility of 0.083 cm2 V-1 s-1 measured in air.

A study of diphenylfumaronitrile and furan-substituted diketopyrrolopyrrole alternating copolymer and its thin-film transistors

A fused aromatic furan-substituted diketopyrrolopyrrole and novel diphenylfumaronitrile conjugated building blocks are used for the synthesis of an alternating copolymer (DPFN-DPPF) via Suzuki polycondensation. In this paper, the first attempt to use the diphenylfumaronitrile building block for the synthesis of conjugated polymer is described. The number-average and weight-average molecular weights calculated for DPFN-DPPF are 20?661 and 66?346 g mol-1, respectively. The optical bandgap calculated for DPFN-DPPF is 1.53 eV whereas the highest occupied molecular orbital (HOMO) value calculated by photoelectron spectroscopy in air (PESA) is 5.50 eV. The calculated HOMO value is lower, which is suitable for stable organic electronic devices. DPFN-DPPF polymer is used as an active layer in bottom-contact bottom-gate organic thin-film transistor devices and the thin film exhibits a hole mobility of 0.20 cm2 V-1 s-1 in air.

Pyridine-incorporated dihexylquaterthiophene : a novel blue emitter for organic light emitting diodes (OLEDs)

The synthesis and characterisation of 2,5-bis(5′-hexyl-[2,2′- bithiophen]-5-yl)pyridine (Th4PY) and its use as a blue emitter in organic light emitting diodes (OLEDs) is reported. Th4PY was synthesised in high yield using a straightforward Suzuki coupling route with commercially available starting materials. As Th4PY is both soluble and has low molecular weight, blue OLEDs were fabricated using both spin-coating and vacuum deposition thin film processing techniques to study the effect of processing on device performance. OLED devices using a spin-coated layer consisting of 4′,4′′- tris(N-carbazolyl)triphenylamine (TCTA) and 2-(4-biphenylyl)-5-(4-tert- butylphenyl)-1,3,4-oxadiazole (PBD) as a host matrix together with Th4PY as emitter exhibited highly efficient sky-blue emission with a low turn-on voltage of 3V, a maximum brightness close to 15000cdm-2 at 8V, and a maximum luminous efficiency of 7.4cdA -1 (6.3lmW -1) with CIE coordinates of x≤0.212, y≤0.320. The device performance characteristics are compared using various matrices and processing techniques. The promising sky-blue OLED performance, solution processability, and ambient stability make Th4PY a promising blue emitter for application in OLEDs.

High-mobility organic thin film transistors based on benzothiadiazole- sandwiched dihexylquaterthiophenes

We report here the synthesis, characterization, and organic thin-film transistor (OTFT) mobilities of 4,7-bis(5-(5-hexylthiophen-2-yl)thiophen-2-yl) benzo[1,2,5]thiadiazole (DH-BTZ-4T). DH-BTZ-4T was prepared in one high-yield step from commercially available materials using Suzuki chemistry and purified by column chromatography. OTFTs with hole mobilities of 0.17 cm2/(Vs) and on/off current ratios of 1 × 105 were prepared from DH-BTZ-4T active layers deposited by vacuum deposition. As DH-BTZ-4T is soluble in common solvents, solution processed devices were also prepared by spin coating yielding preliminary mobilities of 6.0 × 10-3 cm 2/(Vs). The promising mobilities and low band gap (1.90 eV) coupled with solution processability and ambient stability makes this material an excellent candidate for application in organic electronics.

A benzothiadiazole end capped donor–acceptor based small molecule for organic electronics

A benzothiadiazole end-capped small molecule 3,6-bis(5-(benzo[c][1,2,5] thiadiazol-4-yl)thiophen-2-yl)-2,5-bis(2-butyloctyl)pyrrolo[3,4-c]pyrrole-1, 4(2H,5H)-dione (BO-DPP-BTZ) using a fused aromatic moiety DPP (at the centre) is designed and synthesized. BO-DPP-BTZ is a donor-acceptor-donor (D-A-D) structure which possesses a band gap of 1.6 eV and exhibits a strong solid state ordering inferred from ∼120 nm red shift of the absorption maxima from solution to thin film. Field-effect transistors utilizing a spin coated thin film of BO-DPP-BTZ as an active layer exhibited a hole mobility of 0.06 cm 2 V-1 s-1. Solution-processed bulk heterojunction organic photovoltaics employing a blend of BO-DPP-BTZ and [70]PCBM demonstrated a power conversion efficiency of 0.9%.

Relation between charge carrier mobility and lifetime in organic photovoltaics

The relationship between charge carrier lifetime and mobility in a bulk heterojunction based organic solar cell, utilizing diketopyrrolopyrole- naphthalene co-polymer and PC71BM in the photoactive blend layer, is investigated using the photoinduced charge extraction by linearly increasing voltage technique. Light intensity, delay time, and temperature dependent experiments are used to quantify the charge carrier mobility and density as well as the temperature dependence of both. From the saturation of photoinduced current at high laser intensities, it is shown that Langevin-type bimolecular recombination is present in the studied system. The charge carrier lifetime, especially in Langevin systems, is discussed to be an ambiguous and unreliable parameter to determine the performance of organic solar cells, because of the dependence of charge carrier lifetime on charge carrier density, mobility, and type of recombination. It is revealed that the relation between charge mobility (μ) and lifetime (τ) is inversely proportional, where the μτ product is independent of temperature. The results indicate that in photovoltaic systems with Langevin type bimolecular recombination, the strategies to increase the charge lifetime might not be beneficial because of an accompanying reduction in charge carrier mobility. Instead, the focus on non-Langevin mechanisms of recombination is crucial, because this allows an increase in the charge extraction rate by improving the carrier lifetime, density, and mobility simultaneously. © 2013 AIP Publishing LLC.

Nanoscale phase domain structure and associated device performance of organic solar cells based on a diketopyrrolopyrrole polymer

We investigate the blend morphology and performance of bulk heterojunction organic photovoltaic devices comprising the donor polymer, pDPP-TNT (poly{3,6-dithiophene-2-yl-2,5-di(2-octyldodecyl)-pyrrolo[3,4-c]pyrrole-1, 4-dione-alt-naphthalene}) and the fullerene acceptor, [70]PCBM ([6,6]-phenyl C71-butyric acid methyl ester). The blend morphology is heavily dependent upon the solvent system used in the fabrication of thin films. Thin films spin-coated from chloroform possess a cobblestone-like morphology, consisting of thick, round-shaped [70]PCBM-rich mounds separated by thin polymer-rich valleys. The size of the [70]PCBM domains is found to depend on the overall film thickness. Thin films spin-coated from a chloroform:dichlorobenzene mixed solvent system are smooth and consist of a network of pDPP-TNT nanofibers embedded in a [70]PCBM-rich matrix. Rinsing the films in hexane selectively removes [70]PCBM and allows for analysis of domain size and purity. It also provides a means for investigating exciton dissociation efficiency through relative photoluminescence yield measurements. Devices fabricated from chloroform solutions show much poorer performance than the devices fabricated from the mixed solvent system; this disparity in performance is seen to be more pronounced with increasing film thickness. The primary cause for the improved performance of devices fabricated from mixed solvents is attributed to the greater donor-acceptor interfacial area and resulting greater capacity for charge carrier generation.

Measurement of contact voltage drop and resistance in organic solar cells

Bulk heterojunction organic solar cells based on poly[4,7-bis(3- dodecylthiophene-2-yl) benzothiadiazole-co-benzothiadiazole] and [6,6]-phenyl C71-butyric acid methyl ester are investigated. A prominent kink is observed in the fourth quadrant of the current density-voltage (J-V) response. Annealing the active layer prior to cathode deposition eliminates the kink. The kink is attributed to an extraction barrier. The J-V response in these devices is well described by a power law. This behavior is attributed to an imbalance in charge carrier mobility. An expected photocurrent for the device displaying a kink in the J-V response is determined by fitting to a power law. The difference between the expected and measured photocurrent allows for the determination of a voltage drop within the device. Under simulated 1 sun irradiance, the peak voltage drop and contact resistance at short circuit are 0.14 V and 90 Ω, respectively. © 2012 American Institute of Physics.

Valuing the influence of underlying attitudes and the demand for organic milk in Japan

Subjective perceptions about a product affect consumer choice. Accordingly, acquiring the underlying demand characteristics that consumers find desirable is vital for firms planning future marketing strategies. However, the extent to which product-specific perceptions affect consumer choice is poorly understood. New agricultural standards for organic livestock were introduced in Japan in November 2005 and are expected to influence the market significantly. Choice modeling (CM) is used to explore how consumers evaluate the latent demands and conventional attributes (or tangible values) of organic milk. The results suggest that latent demands, along with socioeconomic characteristics and conventional attributes, provide strong incentives for consumers to move from the purchase of conventional milk to organic milk. The analysis indicates that latent demands reflecting the safeness of organic milk, the better taste of organic milk, the image of environmental friendliness in the production process, and the image of the health and comfort of the cows are important factors that influence consumers' purchasing decisions. However, each specific factor has a corresponding conventional tangible attribute that needs to be targeted in marketing strategy.

Three-dimensional off-design numerical analysis of an organic Rankine cycle radial-inflow turbine

Optimisation of organic Rankine cycles(ORCs for binary cycle applications could play a major role in determining the competitiveness of low to moderate renewable sources. An important aspect of the optimisation is to maximise the turbine output power for a given resource. This requires careful attention to the turbine design notably through numerical simulations. Challenges in the numerical modelling of radial-inflow turbines using high-density working fluids still need to be addressed in order to improve the turbine design and better optimise ORCs. Thispaper presents preliminary 3D numerical simulations of a high-density radial-inflow ORC turbine in sensible geothermal conditions. Following extensive investigation of the operating conditions and thermodynamic cycle analysis, therefrigerant R143a is chosen as the high-density working fluid. The 1D design of the candidate radial-inflow turbine is presented in details. Furthermore, commercially-available software Ansys-CFX is used to perform preliminary steady-state 3D CFD simulations of the candidate R143a radial-inflow turbine for a number of operating conditions including off-design conditions. The real-gas properties are obtained using the Peng–Robinson equations of state.The thermodynamic ORC cycle is presented. The preliminary design created using dedicated radial-inflow turbine software Concepts-Rital is discussed and the 3D CFD results are presented and compared against the meanline analysis.

Greenhouse gas emissions from sub-tropical agricultural soils after addition of organic by-products

As the cost of mineral fertilisers increases globally, organic soil amendments (OAs) from agricultural sources are increasingly being used as substitutes for nitrogen. However, the impact of OAs on the production of greenhouse gases (CO2 and N2O) is not well understood. A 60-day laboratory incubation experiment was conducted to investigate the impacts of applying OAs (equivalent to 296 kg N ha−1 on average) on N2O and CO2 emissions and soil properties of clay and sandy loam soils from sugar cane production. The experiment included 6 treatments, one being an un-amended (UN) control with addition of five OAs being raw mill mud (MM), composted mill mud (CM), high N compost (HC), rice husk biochar (RB), and raw mill mud plus rice husk biochar (MB). These OAs were incubated at 60, 75 and 90% water-filled pore space (WFPS) at 25°C with urea (equivalent to 200 kg N ha−1) added to the soils thirty days after the incubation commenced. Results showed WFPS did not influence CO2 emissions over the 60 days but the magnitude of emissions as a proportion of C applied was RB < CM < MB < HC