Polymer electrodes made of poly(3,4-ethylenedioxythiophene):polystyrene sulfonate (PEDOT:PSS) are used in many applications but are also sensitive to humidity. We study humidity-induced changes of PEDOT:PSS electrodes as monitored with in situ time-of-flight neutron reflectivity (TOF-NR) measurements under high humidity conditions. The influence of the solvent additive Zonyl and a post-treatment of PEDOT:PSS films with ethylene glycol (EG) serving as electrodes are analyzed with respect to the swelling ratio and water uptake. Depending on the applied PEDOT:PSS treatment, PEDOT and PSS enrichment layers are clearly identified with TOF-NR at the substrate-polymer and polymer-air interface, respectively. The additive Zonyl reduces the water uptake and limits film swelling. EG post-treatment further increases hydrophobicity and thereby water incorporation into the PEDOT:PSS film is strongly suppressed. The characteristic time constants and effective interaction parameters extracted from the kinetic NR data show that additive and post-treatment reduce the sensitivity of the PEDOT:PSS electrodes to humidity.

Charge transport properties in organic semiconductors depend strongly on molecular order. Here we demonstrate field-effect transistors where drain current flows through a precisely defined array of nanostripes made of crystalline and highly ordered molecules. The molecular stripes are fabricated across the channel of the transistor by a stamp-assisted deposition of the molecular semiconductors from a solution. As the solvent evaporates, the capillary forces drive the solution to form menisci under the stamp protrusions. The solute precipitates only in the regions where the solution is confined by the menisci once the critical concentration is reached and self-organizes into molecularly ordered stripes 100-200 nm wide and a few monolayers high. The charge mobility measured along the stripes is 2 orders of magnitude larger than the values measured for spin-coated thin films.

The effect of an environmentally friendly alcohol treatment on bulk heterojunction (BHJ) polymer solar cells using the low-bandgap copolymer based on thieno[3,4-b]thiophene-alt-benzodithiophene units and [6,6]-phenyl-C71-butyric acid methyl ester is systematically investigated. Different alcohols are tested, and besides the most commonly used methanol treatment, other alcohols such as ethanol, 2-propanol, and 1-butanol also improve the device performance to certain extents as compared to the untreated solar cells. Changes of the surface structure caused by the alcohol treatment are probed with atomic force microscopy, and the modification of inner film morphology is probed by time-of-flight-grazing incidence small-angle neutron scattering (TOF-GISANS). UV/vis measurements show that the thickness of all BHJ films remains unchanged by the different solvent treatments. Thus, the enhanced device performance induced by the alcohol treatments is correlated to the reconstruction of the inner film structures probed with TOF-GISANS and the modified energy levels at the interfaces between the BHJ layer and the aluminum electrodes, evident by the enhanced short-circuit current and open-circuit voltage of the I-V curves.

The lateral structure of an ABA-type triblock copolymer polyparamethylstyrene-block-polystyrene-blockpolyparamethylstyrene at the buried silicon substrate interface is studied as a function of different substrate surface treatments. With grazing incidence small-angle neutron scattering (GISANS), high interface sensitivity is reached. With GISANS, the orientation and degree of order of the morphology are probed. The powderlike oriented lamellar structure in the bulk orients along the surface normal in the vicinity of the substrate. A modification of the short-ranged interface potential of the substrate introduces a lateral stretching of this lamellar structure of up to 8% as compared to the bulk. The decay in stretching toward the volume structure is probed with depth profiling. It extends at least up to a distance of 51 nm from the solid surface.

The swelling and phase transition behavior upon increasing temperature of a doubly thermoresponsive diblock copolymer thin film in steps above the characteristic cloud points (CPs) of the blocks is studied. An upper critical solution temperature (UCST)-type zwitterionic poly-(sulfobetaine), poly(N,N-dimethyl-N-(3-methacrylamidopropyl)-ammoniopropane sulfonate) (PSPP, CP UCST = 31.5 °C), is combined with a lower critical solution temperature (LCST)-type nonionic poly(N-isopropyl-/ methacrylamide) (PNIPMAM, CP LCST = 49.5 °C) block. Using time-offlight neutron reflectivity (ToF-NR), we observe the swelling in D 2 O vapor at a constant temperature of 20 °C, followed by two subsequent temperature jumps, from 20 to 40 °C (above CP UCST ) and from 40 to 60 °C (above CP LCST ). The observed response of the diblock copolymer films deviates from the aqueous solution behavior, which is mainly attributed to the increased polymer concentration. Temperature-induced changes in the thin-film nanostructure are investigated with ToF grazing-incidence small-angle neutron scattering (GISANS). Alterations in the chain conformation and hydrogen bonding are probed by Fourier transform infrared (FTIR) spectroscopy. The ionic SO 3 − groups (in the PSPP block) and the nonionic hydrophilic amide groups (in both blocks) are found to affect the mechanisms of D 2 O uptake and release significantly.

The humidity-induced swelling and exchange behavior of a block copolymer thin film, which consists of a zwitterionic poly­(sulfobetaine) [poly­(N,N-dimethyl-N-(3-(methacrylamido)­propyl)­ammoniopropanesulfonate) (PSPP)] block and a nonionic poly­(N-isopropylacrylamide) (PNIPAM) block, are investigated by time-of-flight neutron reflectometry (TOF-NR). We monitor in situ the swelling in the H2O atmosphere, followed by an exchange with D2O. In the reverse experiment, swelling in the D2O atmosphere and the subsequent exchange with H2O are studied. Both, static and kinetic TOF-NR measurements indicate significant differences in the interactions between the PSPP80-b-PNIPAM130 thin film and H2O or D2O, which we attribute to the different H- and D-bonds between water and the polymer. Changes in the chain conformation and hydrogen bonding are probed with Fourier transform infrared spectroscopy during the kinetics of the swelling and exchange processes, which reveals the key roles of the ionic SO3 – group in the PSPP block and of the polar amide groups of both blocks during water uptake and exchange.

The structure of porous TiO 2 films and TiO 2 :poly(Nvinylcarbazole) (PVK) composite films is investigated with time-offlight grazing incidence small-angle neutron scattering (TOF-GISANS). The TiO 2 films have been prepared by application of a sol-gel process with a diblock copolymer as structure directing agent, and the conductive polymer PVK is infiltrated in the porous network by spin coating and solution casting. The films show a hierarchical pore structure with mesopores 52 nm in size and additional large macropores with a diameter of about 180 nm. By matching the scattering contrast of the TiO 2 with the polymer information about the penetration of the polymer in the pores is determined. Whereas in the PVK film prepared by solution casting the pores are filled to a high degree; in the spin coated film, PVK wets only the TiO 2 pore walls and forms a solid overlying layer.

The powder‐like orientation of lamellar domains in thin films of the diblock copolymer polystyrene‐block‐poly(methyl methacrylate) is investigated using grazing‐incidence small‐angle X‐ray scattering (GISAXS) and grazing‐incidence small‐angle neutron scattering (GISANS). Conventional monochromatic GISANS and GISAXS measurements are compared with neutron time‐of‐flight GISANS. For angles of incidence and exit larger than the critical angle of total external reflection of the polymer, Debye–Scherrer rings are observed. The position of the Debye–Scherrer rings is described quantitatively based on a reduced version of the distorted‐wave Born approximation. A strong distortion of the ring shape is caused by refraction and reflections from the film interfaces. Close to the critical angle, the ring shape collapses into a banana shape.