Poly(2,5-bis(2-octyldodecyl)-3,6-di(furan-2-yl)-2,5-dihydro-pyrrolo[3,4-c] pyrrole-1,4-dione-co-thieno[3,2-b]thiophene): A high performance polymer semiconductor for both organic thin film transistors and organic photovoltaics

A new diketopyrrolopyrrole (DPP)-containing donor-acceptor polymer, poly(2,5-bis(2-octyldodecyl)-3,6-di(furan-2-yl)-2,5-dihydro-pyrrolo[3,4-c] pyrrole-1,4-dione-co-thieno[3,2-b]thiophene) (PDBF-co-TT), is synthesized and studied as a semiconductor in organic thin film transistors (OTFTs) and organic photovoltaics (OPVs). High hole mobility of up to 0.53 cm 2 V -1 s -1 in bottom-gate, top-contact OTFT devices is achieved owing to the ordered polymer chain packing and favoured chain orientation, strong intermolecular interactions, as well as uniform film morphology of PDBF-co-TT. The optimum band gap of 1.39 eV and high hole mobility make this polymer a promising donor semiconductor for the solar cell application. When paired with a fullerene acceptor, PC 71BM, the resulting OPV devices show a high power conversion efficiency of up to 4.38% under simulated standard AM1.5 solar illumination.

3,6-Di(furan-2-yl)pyrrolo[3,4-c]pyrrole-1,4(2H,5H)-dione and bithiophene copolymer with rather disordered chain orientation showing high mobility in organic thin film transistors

Pyrrolo[3,4-c]pyrrole-1,4(2H,5H)-dione or diketopyrrolopyrrole (DPP) is a useful electron-withdrawing fused aromatic moiety for the preparation of donor-acceptor polymers as active semiconductors for organic electronics. This study uses a DPP-furan-containing building block, 3,6-di(furan-2-yl)pyrrolo[3,4- c]pyrrole-1,4(2H,5H)-dione (DBF), to couple with a 2,2′-bithiophene unit, forming a new donor-acceptor copolymer, PDBFBT. Compared to its structural analogue, 3,6-di(thiophen-2-yl)pyrrolo[3,4-c]pyrrole-1,4(2H,5H)-dione (DBT), DBF is found to cause blue shifts of the absorption spectra both in solution and in thin films and a slight reduction of the highest occupied molecular orbital (HOMO) energy level of the resulting PDBFBT. Despite the fact that its thin films are less crystalline and have a rather disordered chain orientation in the crystalline domains, PDBFBT shows very high hole mobility up to 1.54 cm 2 V-1 s-1 in bottom-gate, top-contact organic thin film transistors.

Solution processable poly(2,5-dialkyl-2,5-dihydro-3,6-di-2-thienyl- pyrrolo[3,4-c]pyrrole-1,4-dione) for ambipolar organic thin film transistors

Solution processable diketopyrrolopyrrole (DPP)-bithiophene polymers (PDBT) with long branched alkyl side chains on the DPP unit are synthesized. These polymers have favourable highest occupied molecular orbital (HOMO) and lowest unoccupied molecular orbital (LUMO) energy levels for the injection and transport of both holes and electrons. Organic thin film transistors (OTFTs) using these polymers as semiconductors and gold as source/drain electrodes show typical ambipolar characteristics with very well balanced high hole and electron mobilities (μ h = 0.024 cm 2 V -1 s -1 and μ e = 0.056 cm 2 V -1 s -1). These simple and high-performing polymers are promising materials for ambipolar organic thin film transistors for low-cost CMOS-like logic circuits.

High performance all-carbon thin film supercapacitors

We fabricated high performance supercapacitors by using all carbon electrodes, with volume energy in the order of 10−3 Whcm−3, comparable to Li-ion batteries, and power densities in the range of 10 Wcm−3, better than laser-scribed-graphene supercapacitors. All-carbon supercapacitor electrodes are made by solution processing and filtering electrochemically-exfoliated graphene sheets mixed with clusters of spontaneously entangled multiwall carbon nanotubes. We maximize the capacitance by using a 1:1 weight ratio of graphene to multi-wall carbon nanotubes and by controlling their packing in the electrode film so as to maximize accessible surface and further enhance the charge collection. This electrode is transferred onto a plastic-paper-supported double-wall carbon nanotube film used as current collector. These all-carbon thin films are combined with plastic paper and gelled electrolyte to produce solid-state bendable thin film supercapacitors. We assembled supercapacitor cells in series in a planar configuration to increase the operating voltage and find that the shape of our supercapacitor film strongly affects its capacitance. An in-line superposition of rectangular sheets is superior to a cross superposition in maintaining high capacitance when subject to fast charge/discharge cycles. The effect is explained by addressing the mechanism of ion diffusion into stacked graphene sheets.

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.

Investigation of RuO2/Ta2O5 thin film evolution by thermogravimetry combined with mass spectrometry

The thermal evolution process of RuO2–Ta2O5/Ti coatings with varying noble metal content has been investigated under in situ conditions by thermogravimetry combined with mass spectrometry. The gel-like films prepared from alcoholic solutions of the precursor salts (RuCl3·3H2O, TaCl5) onto titanium metal support were heated in an atmosphere containing 20% O2 and 80% Ar up to 600 °C. The evolution of the mixed oxide coatings was followed by the mass spectrometric ion intensity curves. The cracking of retained solvent and the combustion of organic surface species formed were also followed by the mass spectrometric curves. The formation of carbonyl- and carboxylate-type surface species connected to the noble metal was identified by Fourier transform infrared emission spectroscopy. These secondary processes–catalyzed by the noble metal–may play an important role in the development of surface morphology and electrochemical properties. The evolution of the two oxide phases does not take place independently, and the effect of the noble metal as a combustion catalyst was proved.

Thin-film elemental analyses for precise characterization of minerals

The Analytical Electron Microscope (AEM), with which secondary X-ray emission from a thin (<150nm), electron-transparent material is measured, has rapidly become a versatile instrument for qualitative and quantitative elemental analyses of many materials, including minerals. With due regard for sources of error in experimental procedures, it is possible to obtain high spatial resolution (~20nm diameter) and precise elemental analyses (~3% to 5% relative) from many silicate minerals. In addition, by utilizing the orientational dependence of X-ray emission for certain multi-substituted crystal structures, site occupancies for individual elements within a unit cell can be determined though with lower spatial resolution. The relative ease with which many of these compositional data may be obtained depends in part on the nature of the sample, but, in general, is comparable to other solid state analytical techniques such as X-ray diffraction and electron microprobe analysis. However, the improvement in spatial resolution obtained with the AEM (up to two orders of magnitude in analysis diameter) significantly enhances interpretation of fine-grained assemblages in many terrestrial or extraterrestrial rocks.

Pt/ZnO/SiC thin film for hydrogen gas sensing

Zinc oxide (ZnO) is one of the most promising electronic and photonic materials to date. In this work, we present an enhanced ZnO Schottky gas sensor deposited on SiC substrates in comparison to those reported previously in literature. The performance of ZnO/SiC based Schottky thin film gas sensors produced a forward lateral voltage shift of 12.99mV and 111.87mV in response to concentrations of hydrogen gas at 0.06% and 1% in air at optimum temperature of 330 ºC. The maximum change in barrier height was calculated as 37.9 meV for 1% H2 sensing operation at the optimum temperature.

Numerical solutions for thin film flow down the outside and inside of a vertical cylinder

We consider a model for thin film flow down the outside and inside of a vertical cylinder. Our focus is to study the effect that the curvature of the cylinder has on the gravity-driven instability of the advancing contact line and to simulate the resulting fingering patterns that form due to this instability. The governing partial differential equation is fourth order with a nonlinear degenerate diffusion term that represents the stabilising effect of surface tension. We present numerical solutions obtained by implementing an efficient alternating direction implicit scheme. When compared to the problem of flow down a vertical plane, we find that increasing substrate curvature tends to increase the fingering instability for flow down the outside of the cylinder, whereas flow down the inside of the cylinder substrate curvature has the opposite effect. Further, we demonstrate the existence of nontrivial travelling wave solutions which describe fingering patterns that propagate down the inside of a cylinder at constant speed without changing form. These solutions are perfectly analogous to those found previously for thin film flow down an inclined plane.

Microstructure of an artificial grain boundary weak link in an YBa2Cu3O(7-δ) thin film grown on a (100)(110), [001]-tilt Y-ZrO2 bicrystal

The microstructure of an artificial grain boundary in an YBa2Cu3O7-δ (YBCO) thin film grown on a (100)(110), [001]-tilt yttria-stabilized-zirconia (YSZ) bicrystal substrate has been studied using transmission electron microscopy (TEM). The orientation relationship between the YBCO film and the YSZ substrate was [001]YBCO∥[001]YSZ and [110]YBCO∥[100]YSZ for each half of the bicrystal film. However, the exact boundary geometry of the bicrystal substrate was not transferred to the film. The substrate boundary was straight while the film boundary was wavy. In several cases there was bending of the lattice confined within a distance of a few basal-plane lattice spacings from the boundary plane and microfaceting. No intergranular secondary phase was observed but about 25% of the boundary was covered by c-axis-tilted YBCO grains and a-axis-oriented grains, both of which were typically adjacent to CuO grains or surrounded by a thin Cu-rich amorphous layer.

Charge transport study of high mobility polymer thin-film transistors based on thiophene substituted diketopyrrolopyrrole copolymers

In this paper, we report on the device physics and charge transport characteristics of high-mobility dual-gated polymer thin-film transistors with active semiconductor layers consisting of thiophene flanked DPP with thienylene-vinylene-thienylene (PDPP-TVT) alternating copolymers. Room temperature mobilities in these devices are high and can exceed 2 cm2 V-1 s-1. Steady-state and non-quasi-static measurements have been performed to extract key transport parameters and velocity distributions of charge carriers in this copolymer. Charge transport in this polymer semiconductor can be explained using a Multiple-Trap-and-Release or Monroe-type model. We also compare the activation energy vs. field-effect mobility in a few important polymer semiconductors to gain a better understanding of transport of DPP systems and make appropriate comparisons.

Synthesis, thin-film morphology, and comparative study of bulk and bilayer heterojunction organic photovoltaic devices using soluble diketopyrrolopyrrole molecules

Diketopyrrolopyrrole (DPP)-based organic semiconductors EH-DPP-TFP and EH-DPP-TFPV with branched ethyl-hexyl solubilizing alkyl chains and end capped with trifluoromethyl phenyl groups were designed and synthesized via Suzuki coupling. These compounds show intense absorptions up to 700 nm, and thin film-forming characteristics that sensitively depend on the solvent and coating conditions. Both materials have been used as electron donors in bulk heterojunction and bilayer organic photovoltaic (OPV) devices with fullerenes as acceptors and their performance has been studied in detail. The best power conversion efficiency of 3.3% under AM1.5G illumination (100 mW cm -2) was achieved for bilayer solar cells when EH-DPP-TFPV was used with C 60, after a thermal annealing step to induce dye aggregation and interdiffusion of C 60 with the donor material. To date, this is one of the highest efficiencies reported for simple bilayer OPV devices.

A high mobility P-type DPP-thieno[3,2-b]thiophene copolymer for organic thin-film transistors

A copolymer comprising 1,4-diketopyrrolo[3,4-c]pyrrole (DPP) and thieno[3,2-b]thiophene moieties, PDBT-co-TT, shows high hole mobility of up to 0.94 cm2 V-1 s-1 in organic thin-film transistors. The strong intermolecular interactions originated from π-π stacking and donor-acceptor interaction lead to the formation of interconnected polymer networks having an ordered lamellar structure, which have established highly efficient pathways for charge carrier transport.

High mobility diketopyrrolopyrrole (DPP)-based organic semiconductor materials for organic thin film transistors and photovoltaics

In recent years, the electron-accepting diketopyrrolopyrrole (DPP) moiety has been receiving considerable attention for constructing donor-acceptor (D-A) type organic semiconductors for a variety of applications, particularly for organic thin film transistors (OTFTs) and organic photovoltaics (OPVs). Through association of the DPP unit with appropriate electron donating building blocks, the resulting D-A molecules interact strongly in the solid state through intermolecular D-A and π-π interactions, leading to highly ordered structures at the molecular and microscopic levels. The closely packed molecules and crystalline domains are beneficial for intermolecular and interdomain (or intergranular) charge transport. Furthermore, the energy levels can be readily adjusted, affording p-type, n-type, or ambipolar organic semiconductors with highly efficient charge transport properties in OTFTs. In the past few years, a number of DPP-based small molecular and polymeric semiconductors have been reported to show mobility close to or greater than 1 cm2 V -1 s-1. DPP-based polymer semiconductors have achieved record high mobility values for p-type (hole mobility: 10.5 cm2 V-1 s-1), n-type (electron mobility: 3 cm2 V-1 s-1), and ambipolar (hole/electron mobilities: 1.18/1.86 cm2 V-1 s-1) OTFTs among the known polymer semiconductors. Many DPP-based organic semiconductors have favourable energy levels and band gaps along with high hole mobility, which enable them as promising donor materials for OPVs. Power conversion efficiencies (PCE) of up to 6.05% were achieved for OPVs using DPP-based polymers, demonstrating their potential usefulness for the organic solar cell technology. This article provides an overview of the recent exciting progress made in DPP-containing polymers and small molecules that have shown high charge carrier mobility, around 0.1 cm2 V-1 s-1 or greater. It focuses on the structural design, optoelectronic properties, molecular organization, morphology, as well as performances in OTFTs and OPVs of these high mobility DPP-based materials.