Perylenediimide (PDI)-based acceptors offer a potential replacement for fullerenes in bulk-heterojunction (BHJ) organic photovoltaic cells (OPVs). The most promising efforts have focused on creating twisted PDI dimers to disrupt aggregation and thereby suppress excimer formation. Here, we present an alternative strategy for developing high-performance OPVs based on PDI acceptors that promote slip-stacking in the solid state, thus preventing the coupling necessary for rapid excimer formation. This packing structure is accomplished by substitution at the PDI 2,5,8,11-positions ("headland positions"). Using this design principle, three PDI acceptors, N,N-bis(n-octyl)-2,5,8,11-tetra(n-hexyl)-PDI (Hexyl-PDI), N,N-bis(n-octyl)-2,5,8,11-tetraphenethyl-PDI (Phenethyl-PDI), and N,N-bis(n-octyl)-2,5,8,11-tetraphenyl-PDI (Phenyl-PDI), were synthesized, and their molecular and electronic structures were characterized. They were then blended with the donor polymer PBTI3T, and inverted OPVs of the structure ITO/ZnO/Active Layer/MoO3/Ag were fabricated and characterized. Of these, 1:1 PBTI3T:Phenyl-PDI proved to have the best performance with Jsc = 6.56 mA/cm(2), Voc = 1.024 V, FF = 54.59%, and power conversion efficiency (PCE) = 3.67%. Devices fabricated with Phenethyl-PDI and Hexyl-PDI have significantly lower performance. The thin film morphology and the electronic and photophysical properties of the three materials are examined, and although all three materials undergo efficient charge separation, PBTI3T:Phenyl-PDI is found to have the deepest LUMO, intermediate crystallinity, and the most well-mixed domains. This minimizes geminate recombination in Phenyl-PDI OPVs and affords the highest PCE. Thus, slip-stacked PDI strategies represent a promising approach to fullerene replacements in BHJ OPVs.

Current transport by tunneling through molecular devices is thought to be dominated by the height and width of the barrier(s) resulting from the presence of molecules between the electrodes. To a first approximation, the barrier height in metal/molecule junctions is given by the energy difference between the Fermi level of the electrode and the closest molecular energy levels, the highest occupied molecular orbital (HOMO) and/or the lowest unoccupied molecular orbital (LUMO). For semiconductor/molecule junctions, the corresponding barrier height is the energy difference between the edge of the conduction or valence band and the LUMO or HOMO, respectively, depending on the semiconductor doping type, and can be tuned by changing the semiconductor doping type.[1] Experimentally the position of the molecules' HOMO and LUMO relative to the electrodes' Fermi level or band edges can be determined using ultraviolet photoemission spectroscopy (UPS) and inverse photoemission spectroscopy (IPES) measurements. Therefore, the tunneling-barrier height through a molecular layer can, in principle, be deduced by using this method.[2]Here, we compare and analyze the electronic transport through alkyl chains, C n H 2n+1 with n = 12, 14, 16, and 18, bound directly to p-or n-Si, via C-Si bonds, and contacted by Hg to form Si-alkyl/Hg junctions. In these molecular junctions the alkyl chains are connected via the same Si-C bonds to either n-or p-Si, with presumably the same amount of charge transfer between the molecule and the electrode as a result of this bond formation. This feature allows us to isolate and ascertain the effect of the electrode Fermi-level position on charge transport through the junction. [3,4] As carried out earlier for the n-Si system only, [5] we now deduce the barriers for charge transport through the alkane monolayers, both from transport through the junctions and from spectroscopic measurements of the corresponding p-and n-Si-C n H 2n+1 interfaces. The main differences in analyses with our earlier n-Si work [5] are that we use a more complete model for transport analysis and that we can now interpret the photoemission data with the help of complementary theoretical computations. [6] In this way, we find that whereas the spectroscopic measurements show a tunnel barrier of approximately 3-4 eV (rather than the smaller one derived earlier [5] without the help of theory to interpret the IPES and UPS data), fitting the current-voltage (I-V) curves to transport by tunneling yields a barrier of only approximately 0.7-1 eV. We show that this difference, which is ascribed to the presence of states at the interface caused by Si molecule interactions beyond Si-C bond formation, forces us to revise our view of tunneling through such molecular junctions. As shown earlier, in a semiconductor/saturated-molecule/ metal junction, two transport barriers can exist simultaneously, a Schottky barrier inside the semiconductor, caused by band bending near the interface, and a tunnel barrier formed by the insulating, r-bonded molecu...

In oxide semiconductors, such as those based on indium zinc oxide (IXZO), a strong oxygen binding metal ion ("oxygen getter"), X, functions to control O vacancies and enhance lattice formation, hence tune carrier concentration and transport properties. Here we systematically study, in the IXZO series, the role of X = Ga(3+) versus the progression X = Sc(3+) → Y(3+) → La(3+), having similar chemical characteristics but increasing ionic radii. IXZO films are prepared from solution over broad composition ranges for the first time via low-temperature combustion synthesis. The films are characterized via thermal analysis of the precursor solutions, grazing incidence angle X-ray diffraction (GIAXRD), atomic force microscopy (AFM), X-ray photoelectron spectroscopy (XPS), and scanning transmission electron microscopy (STEM) with high angle annular dark field (HAADF) imaging. Excellent thin-film transistor (TFT) performance is achieved for all X, with optimal compositions after 300 °C processing exhibiting electron mobilities of 5.4, 2.6, 2.4, and 1.8 cm(2) V(-1) s(-1) for Ga(3+), Sc(3+), Y(3+), and La(3+), respectively, and with I(on)/I(off) = 10(7)-10(8). Analysis of the IXZO TFT positive bias stress response shows X = Ga(3+) to be superior with mobilities (μ) retaining >95% of the prestress values and threshold voltage shifts (ΔV(T)) of <1.6 V, versus <85% μ retention and ΔV(T) ≈ 20 V for the other trivalent ions. Detailed microstructural analysis indicates that Ga(3+) most effectively promotes oxide lattice formation. We conclude that the metal oxide lattice formation enthalpy (ΔH(L)) and metal ionic radius are the best predictors of IXZO oxygen getter efficacy.

Super-resolution three-dimensional (3D) optical microscopy has incomparable advantages over other high-resolution microscopic technologies, such as electron microscopy and atomic force microscopy, in the study of biological molecules, pathways and events in live cells and tissues. We present a novel approach of structured illumination microscopy (SIM) by using a digital micromirror device (DMD) for fringe projection and a low-coherence LED light for illumination. The lateral resolution of 90 nm and the optical sectioning depth of 120 μm were achieved. The maximum acquisition speed for 3D imaging in the optical sectioning mode was 1.6×107 pixels/second, which was mainly limited by the sensitivity and speed of the CCD camera. In contrast to other SIM techniques, the DMD-based LED-illumination SIM is cost-effective, ease of multi-wavelength switchable and speckle-noise-free. The 2D super-resolution and 3D optical sectioning modalities can be easily switched and applied to either fluorescent or non-fluorescent specimens.

A novel ferrocenium capped amphiphilic pillar[5]arene (FCAP) was synthesized and self-assembled to cationic vesicles in aqueous solution. The cationic vesicles, displaying low cytotoxicity and significant redox-responsive behavior due to the redox equilibrium between ferrocenium cations and ferrocenyl groups, allow building an ideal glutathione (GSH)-responsive drug/siRNA co-delivery system for rapid drug release and gene transfection in cancer cells in which higher GSH concentration exists. This is the first report of redox-responsive vesicles assembled from pillararenes for drug/siRNA co-delivery; besides enhancing the bioavailability of drugs for cancer cells and reducing the adverse side effects for normal cells, these systems can also overcome the drug resistance of cancer cells. This work presents a good example of rational design for an effective stimuli-responsive drug/siRNA co-delivery system.