Star-shape non-fullerene acceptor featuring an aza-triangulene core for organic solar cells.

We present the simple synthesis of a star-shape non-fullerene acceptor (NFA) for application in organic solar cells. This NFA possesses a D(A)3 structure in which the electron-donating core is an aza-triangulene unit and we report the first crystal structure for a star shape NFA based on this motive. We fully characterized this molecule's optoelectronic properties in solution and thin films, investigating its photovoltaic properties when blended with PTB7-Th as the electron donor component. We demonstrate that the aza-triangulene core leads to a strong absorption in the visible range with an absorption edge going from 700 nm in solution to above 850 nm in the solid state. The transport properties of the pristine molecule were investigated in field effect transistors (OFETs) and in blends with PTB7-Th following a Space-Charge-Limited Current (SCLC) protocol. We found that the mobility of electrons measured in films deposited from o-xylene and chlorobenzene are quite similar (up to 2.70 × 10-4 cm2 V-1 s-1) and that the values are not significantly modified by thermal annealing. The new NFA combined with PTB7-Th in the active layer of inverted solar cells leads to a power conversion efficiency of around 6.3% (active area 0.16 cm2) when processed from non-chlorinated solvents without thermal annealing. Thanks to impedance spectroscopy measurements performed on the solar cells, we show that the charge collection efficiency of the devices is limited by the transport properties rather than by recombination kinetics. Finally, we investigated the stability of this new NFA in various conditions and show that the star-shape molecule is more resistant against photolysis in the presence and absence of oxygen than ITIC.

Low-dose measurement of electric potential distribution in organic light-emitting diode by phase-shifting electron holography with 3D tensor decomposition.

To improve the performance of organic light-emitting diodes (OLEDs), it is essential to understand and control the electric potential in the organic semiconductor layers. Electron holography (EH) is a powerful technique for visualizing the potential distribution with a transmission electron microscope. However, it has a serious issue that high-energy electrons may damage the organic layers, meaning that a low-dose EH is required. Here, we used a machine learning technique, three-dimensional (3D) tensor decomposition, to denoise electron interference patterns (holograms) of bilayer OLEDs composed of N,N'-di-[(1-naphthyl)-N,N'-diphenyl]-(1,1'-biphenyl)-4,4'-diamine (α-NPD) and tris-(8-hydroxyquinoline)aluminum (Alq3), acquired under a low-dose rate of 130 e- nm-2 s-1. The effect of denoising on the phase images reconstructed from the holograms was evaluated in terms of both the phase measurement error and the peak signal-to-noise ratio. We achieved a precision equivalent to that of a conventional measurement that had an exposure time 60 times longer. The electric field within the Alq3 layer decreased as the cumulative dose increased, which indicates that the Alq3 layer was degraded by the electron irradiation. On the basis of the degradation of the electric field, we concluded that the tolerance dose without damaging the OLED sample is about 1.7 × 105 e- nm-2, which is about 0.6 times that of the conventional EH. The combination of EH and 3D tensor decomposition denoising is capable of making a time series measurement of an OLED sample without any effect from the electron irradiation.

Phase-shifting electron holography for accurate measurement of potential distributions in organic and inorganic semiconductors.

Phase-shifting electron holography (PS-EH) is an interference transmission electron microscopy technique that accurately visualizes potential distributions in functional materials, such as semiconductors. In this paper, we briefly introduce the features of the PS-EH that overcome some of the issues facing the conventional EH based on Fourier transformation. Then, we present a high-precision PS-EH technique with multiple electron biprisms and a sample preparation technique using a cryo-focused-ion-beam, which are important techniques for the accurate phase measurement of semiconductors. We present several applications of PS-EH to demonstrate the potential in organic and inorganic semiconductors and then discuss the differences by comparing them with previous reports on the conventional EH. We show that in situ biasing PS-EH was able to observe not only electric potential distribution but also electric field and charge density at a GaAs p-n junction and clarify how local band structures, depletion layer widths and space charges changed depending on the biasing conditions. Moreover, the PS-EH clearly visualized the local potential distributions of two-dimensional electron gas layers formed at AlGaN/GaN interfaces with different Al compositions. We also report the results of our PS-EH application for organic electroluminescence multilayers and point out the significant potential changes in the layers. The proposed PS-EH enables more precise phase measurement compared to the conventional EH, and our findings introduced in this paper will contribute to the future research and development of high-performance semiconductor materials and devices.

Direct Correlation of Nanoscale Morphology and Device Performance to Study Photocurrent Generation in Donor-Enriched Phases of Polymer Solar Cells.

The nanoscale morphology of polymer blends is a key parameter to reach high efficiency in bulk heterojunction solar cells. Thereby, research typically focusing on optimal blend morphologies while studying nonoptimized blends may give insight into blend designs that can prove more robust against morphology defects. Here, we focus on the direct correlation of morphology and device performance of thieno[3,4-b]-thiophene-alt-benzodithiophene (PTB7):[6,6]phenyl C71 butyric acid methyl ester (PC71BM) bulk heterojunction (BHJ) blends processed without additives in different donor/acceptor weight ratios. We show that while blends of a 1:1.5 ratio are composed of large donor-enriched and fullerene domains beyond the exciton diffusion length, reducing the ratio below 1:0.5 leads to blends composed purely of polymer-enriched domains. Importantly, the photocurrent density in such blends can reach values between 45 and 60% of those reached for fully optimized blends using additives. We provide here direct visual evidence that fullerenes in the donor-enriched domains are not distributed homogeneously but fluctuate locally. To this end, we performed compositional nanoscale morphology analysis of the blend using spectroscopic imaging of low-energy-loss electrons using a transmission electron microscope. Charge transport measurement in combination with molecular dynamics simulations shows that the fullerene substructures inside the polymer phase generate efficient electron transport in the polymer-enriched phase. Furthermore, we show that the formation of densely packed regions of fullerene inside the polymer phase is driven by the PTB7:PC71BM enthalpy of mixing. The occurrence of such a nanoscale network of fullerene clusters leads to a reduction of electron trap states and thus efficient extraction of photocurrent inside the polymer domain. Suitable tuning of the polymer-acceptor interaction can thus introduce acceptor subnetworks in polymer-enriched phases, improving the tolerance for high-efficiency BHJ toward morphological defects such as donor-enriched domains exceeding the exciton diffusion length.

Acetylenic spacers in phenylene end-substituted oligothiophene core for highly air-stable organic field-effect transistors.

Two thiophene-phenylene semiconductors, bis(2-phenylethynyl) end-substituted oligothiophenes (diPhAc-nTs, n = 2, 3), were synthesized and studied with respect to their optical, electrochemical, structural and electrical properties. The optical and electrochemical properties of the oligomers in solution were investigated by UV-vis absorption and photoluminescence spectroscopies, and cyclic voltammetry. High vacuum evaporated thin films were investigated by optical absorption, X-ray diffraction and AFM, and implemented as p-type semiconducting layers into organic thin-film transistors (OTFTs). A comparative study in solution and in the solid state with distyryl-oligothiophenes (DSnTs, n = 2, 3) reveals the great influence of acetylenic (-C[triple bond]C-) vs. olefinic (-C=C-) spacers in thiophene-phenylene derivatives on electronic structure, physical properties, and device efficiencies. Substituting olefinic for acetylenic pi-spacers in terthiophene-based conjugated semiconductors leads to one of incontrovertible attributes of OTFTs for low cost applications, a high mobility at low substrate temperature (T(sub)) i.e. typically 25 degrees C. Fine-tuning in the HOMO/LUMO levels by reducing the HOMO level introduces increased air-oxidation strength of thin films where OTFTs provide exactly the same hole mobility value after 100 days in air. All the results suggested that introduction of carbon-carbon triple bonds provided an efficient route to highly air-stable organic thin film transistors.

Oligothiophene self-assembly on the surface of ZnO nanorods: toward coaxial p-n hybrid heterojunctions.

We describe herein the design, synthesis and detailed structural characterization of hybrid 1D nanostructures. They are prepared by supramolecular self-assembly of oligothiophene molecules on the surface of zinc oxide nanorods in solution at room temperature. Electronic absorption spectroscopy and X-ray diffraction show that both organic and inorganic components in the coaxial p-n heterojunctions are crystalline. Especially, it is demonstrated that the organic compounds form a self-assembled monolayer at the surface of the nanorods, which is not the case when zinc oxide quantum dots are instead used. As a result of their hybrid nature, the 1D nanostructures lead to ambipolar semiconducting nanostructured materials as active layers in field-effect transistors.

A "kite" shaped styryl end-capped benzo[2,1-b:3,4-b']dithiophene with high electrical performances in organic thin film transistors.

The bridging of distyryl-bithiophene leads to a kite shape of the conjugated system. This twist is not like twistacenes or twist deformation in alpha-oligothiophenes but a curvature such as in bowl shaped systems. Initially perceived to be undesirable, this new semiconductor in OTFT devices provides excellent performances in air, mu = 0.1 cm(2)/V.s, I(on)/I(off) > 10(6), S < 4 V/decade, higher by a factor of 5 to the parent unbridged coplanar analogue.

Model studies of 6,7-indolequinone cofactors of quinoprotein amine dehydrogenases.

The electronic effects of the C-4 substituent on the physicochemical properties and reactivity of the 6,7-inodolequinone cofactors (CTQ and TTQ) have extensively been investigated with use of a series of C-4 substituted 6,7-inodolequinone derivatives (1-4). The one-electron reduction potentials of the 6,7-inodolequinone derivatives decrease with increasing the electron donating ability of the C-4 substituent (with the following order of E degrees': 4>1>2>3). The reaction of indolequinones 1-3 with benzylamine proceeds stepwise through the iminoquinone and the product-imine intermediates to give aminophenol as the final product as the case of TTQ model compound 4. The rate constants of each step have been determined by the detailed kinetic analysis, and the kinetic deuterium isotope effects have also been examined to confirm the rate-determining step. The reactivity of CTQ model compound 1 toward the amines is by one order of magnitude lower than that of TTQ model compound 4. The reactivity of indolequinones 2 and 3 is further decreased due to their stronger electron-donating substituents at C-4. A more important difference between CTQ model compound 1 and TTQ model compound 4 is the reactivity of the iminoquinone intermediate: the reaction of the CTQ model compound with amines stops at the iminoquinone formation stage at room temperature, whereas the reaction of the TTQ model compound with amines proceeds up to the aminophenol formation. Thus, the energy barrier for the rearrangement of the iminoquinone to the product-imine is higher in the CTQ model system than in the TTQ model system.

Alpha,omega-distyryl oligothiophenes: high mobility semiconductors for environmentally stable organic thin film transistors.

Critical to the development of organic electronics is the design and synthesis of new organic semiconductors with improved electrical performance and enhanced environmental stability. We present in this communication the synthesis of a series of simple oligothiophene derivatives that bear the styryl unit as terminal substituent. Thin film field-effect transistors incorporating these compounds show high electrical performance, such as mobilities as high as 0.1 cm2/Vs, along with exceptional stability under ambient conditions. Especially, the longer oligomer, DS-4T, containing the quaterthiophene core gives rise to devices that show no decrease in performance after more than 17 months of storage and under continuous operation. Such stability features are unprecedented in the oligothiophene series.

[Vascular reconstructive surgery for elderly patients with internal carotid artery stenosis at the cervical portion].

PURPOSE: We encounted increasing numbers of elderly patients suffering from stenotic lesions of the cervical internal carotid artery. Most of them have been considered to indicate a need for carotid artery stenting. The purpose of this study was to clarify with regard to the modality of treatment and perioperative complications the effectiveness of vascular reconstruction procedure in elderly patients. PATIENTS AND METHODS: Ninety eight lesions in 91 patients with stenosis of the internal carotid artery were treated surgically. Eighty lesions received carotid endarterectomy (CEA), and 18 lesions received percutaneous transluminal angioplasty (PTA) with or without stent. Treatment with PTA-with-or-without-stent has been opted in cases of patient with such conditions as radiation-induced stenosis, re-stenosis after CEA, unfitness for general anesthesia, bilateral lesions both of which need to be reconstructed with in a short interval. We divided the patients into 4 groups according to their age; under 70-year-old group, 70-to-74-year old group, 75-to-79-year old group, and over 80-year-old group. Vasoreconstructive procedures were performed for 41 patients in the under 70-year-old group, for 31 in the 70-to-74-year old group, for 21 in the 75-to-79-year old group, and for 5 in the over 80-year-old group. RESULT: The overall surgical morbidity rate was 2% (2 of 98 cases) and there was no mortality. Tweleve patients (12.2%) experienced transient neurological deficits. Two patients exhibited perioperative complications in gastrointestinal organs, but none of the patients experienced cardiac complications. Elderly patients tend to experience systemic complications such as gastrointestinal complications as well as transient neurological deficits, which appear as restlessness, possibly due to hyperperfusion syndrome. The perioperative complication rate in elderly patients (putting the patients of the 70-to-74-year old group, the 75-to-79-year old group, and the over 80-year-old group together) was, statistically, significantly higher than those in patients of under the 70-year-old group. However, when two treatment modalities, CEA and PTA-with-or-without stent, were compared, there was no significant difference in the perioperative complication rate. CONCLUSION: Careful patient selection and prudent perioperative management enabled us to perform vasoreconstructive surgery even for elderly patients with internal carotid artery stenosis in a relatively safe manner with an acceptable complication rate. Decision making in selecting treatment modality, CEA or PTA with or without stent, should not be based solely on aging.