Marcus Halik

High shunt resistance in polymer solar cells comprising a MoO3 hole extraction layer processed from nanoparticle suspension

In this report, we present solution processed molybdenum trioxide (MoO3) layers incorporated as hole extraction layer (HEL) in polymer solar cells (PSCs) and demonstrate the replacement of the commonly employed poly(3,4-ethylene dioxythiophene):(polystyrene sulfonic acid) (PEDOT:PSS). MoO3 is known to have excellent electronic properties and to yield more stable devices compared to PEDOT:PSS. We demonstrate fully functional solar cells with up to 65 nm thick MoO3 HEL deposited from a nanoparticle suspension at low temperatures. The PSCs with an active layer comprising a blend of poly(3-hexylthiophene) and [6,6]-phenyl-C61 butyric acid methyl ester and a MoO3 HEL show comparable performance to reference devices with a PEDOT:PSS HEL. The best cells with MoO3 reach a fill factor of 66.7% and power conversion efficiency of 2.92%. Moreover, MoO3 containing solar cells exhibit an excellent shunt behavior with a parallel resistance of above 100u2002kΩu2009cm2.

A generic interface to reduce the efficiency-stability-cost gap of perovskite solar cells

Minimizing losses at interfaces Among the issues facing the practical use of hybrid organohalide lead perovskite solar cells is the loss of charge carriers at interfaces. Hou et al. show that tantalum-doped tungsten oxide forms almost ohmic contacts with inexpensive conjugated polymer multilayers to create a hole-transporting material with a small interface barrier. This approach eliminates the use of ionic dopants that compromise device stability. Solar cells made with these contacts achieved maximum efficiencies of 21.2% and operated stably for more than 1000 hours. Science, this issue p. 1192 Tantalum-doped tungsten oxide forms nearly ohmic contacts with conjugated polymers to create efficient hole transporters. A major bottleneck delaying the further commercialization of thin-film solar cells based on hybrid organohalide lead perovskites is interface loss in state-of-the-art devices. We present a generic interface architecture that combines solution-processed, reliable, and cost-efficient hole-transporting materials without compromising efficiency, stability, or scalability of perovskite solar cells. Tantalum-doped tungsten oxide (Ta-WOx)/conjugated polymer multilayers offer a surprisingly small interface barrier and form quasi-ohmic contacts universally with various scalable conjugated polymers. In a simple device with regular planar architecture and a self-assembled monolayer, Ta-WOx–doped interface–based perovskite solar cells achieve maximum efficiencies of 21.2% and offer more than 1000 hours of light stability. By eliminating additional ionic dopants, these findings open up the entire class of organics as scalable hole-transporting materials for perovskite solar cells.

Morphology analysis of near IR sensitized polymer/fullerene organic solar cells by implementing low bandgap heteroanalogue C-/Si-PCPDTBT

In the current work, we have investigated the morphological aspects of the ternary solar cells based on host matrices of P3HT:PCBM and P3HT:ICBA, using the low bandgap polymer analogues of C- and Si-bridged PCPDTBT as near IR sensitizers, which show noticeably different performance. A direct comparison of these well-functional and poorly functional ternary blend systems provides insights into the bottlenecks of device performance and enables us to set up an initial set of design rules for ternary organic solar cells. Our study reveals the importance of surface energy as a driving force controlling sensitizer location and morphology formation of ternary blends. The interfacial surface energy results indicate that Si-PCPDTBT locates at amorphous interfaces and P3HT crystallites, while C-PCPDTBT tends to accumulate at amorphous interfaces and semi-crystalline (or agglomerated) domains of the fullerene derivatives. GIWAXS and SCLC results support this prediction where adding high content of C-PCPDTBT influences mainly the semi-crystallinity (aggregation) of the fullerene and reduces the electron mobility, but Si-PCPDTBT impacts mainly the P3HT ordering and, in turn, deteriorates the hole mobility. These findings show that the disruption of the fullerene semi-crystalline domains is more detrimental to the device performance than the disruption of the polymer domains.

A facile approach to synthesize an oxo-functionalized graphene/polymer composite for low-voltage operating memory devices

Memory devices are a key technology of our era and one of the constant challenges is the reduction of their power consumption. Herein, we demonstrate that graphene oxide with very few defects, that is, about 1 nm thin oxo-functionalized graphene derivative, can be used in memory devices operating at 3 V. A memory device stores charges in the material of the active channel. Thereby, writing and erasing information can be performed at low voltage, facilitating low power consumption. To enable operation at low voltage, a novel synthetic approach is necessary. We find that the selective non-covalent electrostatic functionalization of mainly organosulfate ions is possible with dodecylammonium. This functionalization allows the non-covalent coating of flakes with a polystyrene-derivative as nm-thin dielectric medium. The resulting polymer-wrapped composite has a height of about 5 nm. We find that the thin coating of a few nm is mandatory to make the memory device work at low voltage. Furthermore, a self-assembled monolayer of an imidazolium derivative further enhances the function of the memory device. The prepared composite materials are characterized by state-of-the-art analysis including solid state nuclear magnetic resonance spectroscopy and thermogravimetric analysis coupled with gas chromatography, mass spectroscopy or infrared spectroscopy. Reference experiments prove the importance of the controlled synthesis to enable the function of the memory device.

In situ STXM investigations of pentacene-based OFETs during operation

Ultrathin pentacene-based organic field-effect transistors (OFETs) on commercially available silicon nitride membranes suitable for transmission X-ray experiments are demonstrated. The devices produced by high-vacuum deposition show excellent electronic performance (µ = 0.6 cm2 V−1 s−1, Ion/off = 106). STXM-experiments recorded with the PolLux microspectroscope correlate structural and electronic properties at highest spatial and spectral resolution while the OFET is operated. Local NEXAFS spectra are used to analyze the different orientations of the pentacene nanocrystals. Spectral changes due to modifications in the electronic structure during OFET operation can hardly be detected with the current setup.

Modeling charge transport in C60-based self-assembled monolayers for applications in field-effect transistors.

We have investigated the conductance properties of C60-containing self-assembled monolayers (SAMs), which are used in organic field-effect transistors, employing a combination of molecular-dynamics simulations, semiempirical electronic structure calculations, and Landauer transport theory. The results reveal the close relation between the transport characteristics and the structural and electronic properties of the SAM. Furthermore, both local pathways of charge transport in the SAMs and the influence of structural fluctuations are analyzed.

Improving the Performance of Organic Thin-Film Transistors by Ion Doping of Ethylene-Glycol-Based Self-Assembled Monolayer Hybrid Dielectrics.

Tuning the electrostatics of ethylene-glycol-based self-assembled monolayers (SAMs) by doping with ions is shown. Molecular dynamics simulations unravel binding mechanisms and predict dipole strengths of the doped layers. Additionally, by applying such layers as dielectrics in organic thin-film transistors, the incorporated ions are proven to enhance device performance by lowering the threshold voltage and increasing conductivity.

Green Processing of Metal Oxide Core–Shell Nanoparticles as Low‐Temperature Dielectrics in Organic Thin‐Film Transistors

TiO2 , Fe3 O4, AlOx , ITO (indium tin oxide), and CeO2 nanoparticles are tailored to exhibit excellent dispersability in deionized water and alcohols. The latter provides an ecofriendly solution for processing metal oxide nanoparticles at a neutral pH. Water-processed dielectrics from the metal oxide nanoparticles are incorporated into organic thin-film transistors fabricated on rigid and flexible substrates.

Enhanced In Vitro Biocompatibility and Water Dispersibility of Magnetite and Cobalt Ferrite Nanoparticles Employed as ROS Formation Enhancer in Radiation Cancer Therapy

Efficient magnetic reactive oxygen species (ROS) formation enhancing agents after X-ray treatment are realized by functionalizing superparamagnetic magnetite (Fe3 O4 ) and Co-ferrite (CoFe2 O4 ) nanoparticles with self-assembled monolayers (SAMs). The Fe3 O4 and CoFe2 O4 nanoparticles are synthesized using Massarts coprecipitation technique. Successful surface modification with the SAM forming compounds 1-methyl-3-(dodecylphosphonic acid) imidazolium bromide, or (2-{2-[2-hydroxy-ethoxy]-ethoxy}-ethyl phosphonic acid provides biocompatibility and long-term stability of the Fe3 O4 and CoFe2 O4 nanoparticles in cell media. The SAM-stabilized ferrite nanoparticles are characterized with dynamic light scattering, X-ray powder diffraction, a superconducting quantum interference device, Fourier transform infrared attenuated total reflectance spectroscopy, zeta potential measurements, and thermogravimetric analysis. The impact of the SAM-stabilized nanoparticles on the viability of the MCF-7 cells and healthy human umbilical vein endothelial cells (HUVECs) is assessed using the neutral red assay. Under X-ray exposure with a single dosage of 1 Gy the intracellular SAM stabilized Fe3 O4 and CoFe2 O4 nanoparticles are observed to increase the level of ROS in MCF-7 breast cancer cells but not in healthy HUVECs. The drastic ROS enhancement is associated with very low dose modifying factors for a survival fraction of 50%. This significant ROS enhancement effect by SAM-stabilized Fe3 O4 and CoFe2 O4 nanoparticles constitutes their excellent applicability in radiation therapy.