Patterns and structures, formed when a semiconducting polymer blend in solution is subject to controlled evaporation, have been of great interest due to their influence on the performance of organic devices. By controlling the processes of pattern formation, function properties of organic semiconductor structures can be tailored, allowing for facile manufacturing of the active layers in organic devices, e.g. solar cells.

By analyzing the morphologies of polymer blends resulting from different deposition methods, a deeper insight into the pattern formation process can be acquired. In this study, we have analyzed the morphology of blends of poly(3-hexylthiophene) (P3HT) and [6,6]-phenyl-C61-butyric acid methyl ester (PCBM) formed upon solvent evaporation. We used the following deposition methods: dip-coating, droplet evaporation within a constrained geometry and drop-casting. Dip-coated films revealed various types of morphology depending on the coating speed. At low coating speeds, where evaporation is the dominant factor, well-ordered patterns were obtained. When increasing the coating speed, viscous forces become dominant over evaporation yielding optically homogenous films [2]. Morphologically similar structures to those observed at low coating speeds, were also obtained with spatially constrained droplets. The blend morphologies were analyzed with polarized, fluorescence and atomic force microscopy [1].

References:

[1] C. M. Björström Svanström, J. Rysz, A. Bernasik, A. Budkowski, F. Zhang, O. Inganäs, M. R. Andersson, K. O. Magnusson, J. J. Benson-Smith, J. Nelson, and E. Moons, Adv. Mat. 21, 4398-4403 (2009)

[2] R. Z. Rogowski and A. A. Darhuber, Langmuir 26, 11485-93 (2010)

Nanoparticle organic photovoltaics, a subfield of organic photovoltaics (OPV), has attracted increasing interest in recent years due to the eco-friendly fabrication of solar modules afforded by colloidal ink technology. Importantly, using this approach it is now possible to engineer the microstructure of the light absorbing/charge generating layer of organic photovoltaics; decoupling film morphology from film deposition. In this study, single-component nanoparticles of poly(3-hexylthiophene) (P3HT) and phenyl-C61 butyric acid methyl ester (PC61BM) were synthesized and used to generate a two-phase microstructure with control over domain size prior to film deposition. Scanning transmission X-ray microscopy (STXM) and electron microscopy were used to characterize the thin film morphology. Uniquely, the measured microstructure was a direct input for a nanoscopic kinetic Monte Carlo (KMC) model allowing us to assess exciton transport properties that are experimentally inaccessible in these single-component particles. Photoluminescence, UV-vis spectroscopy measurements, and KMC results of the nanoparticle thin films enabled the calculation of an experimental exciton dissociation efficiency (ηED) of 37% for the two-phase microstructure. The glass transition temperature (Tg) of the materials was characterized with dynamic mechanical thermal analysis (DMTA) and thermal annealing led to an increase in ηED to 64% due to an increase in donor-acceptor interfaces in the thin film from both sintering of neighboring opposite-type particles in addition to the generation of a third mixed phase from diffusion of PC61BM into amorphous P3HT domains. As such, this study demonstrates the higher level of control over donor-acceptor film morphology enabled by customizing nanoparticulate colloidal inks, where the optimal three-phase film morphology for an OPV photoactive layer can be designed and engineered.

The challenge of coating organic photovoltaics (OPV) from green solvents is to achieve the requirednanostructured interpenetrating network of donor and acceptor domains based on a rational choice ofsolvent approach as opposed to the usual trial-and-error methods. We demonstrate here that we canachieve a bicontinuous interpenetrating network with nanoscale phase separation for the chosen donor–acceptor material system poly[2,3-bis-(3-octyloxyphenyl)quinoxaline-5,8-diyl-alt-thiophene-2,5-diyl]:phenyl-C61 butyric acid methyl ester (TQ1:PC61BM) when processing from green solvent ink formulations.This structure is achieved by first calculating the Hansen solubility parameters (HSP) of the donor andacceptor materials, followed by careful choice of solvents with selective relative solubilities for the twomaterials based on the desired order of precipitation necessary for forming a nanostructured interdigitatednetwork morphology. We found that the relative distances in Hansen space (Ra) between TQ1 andthe primary solvent, on the one hand, and PC61BM and the primary solvent, on the other hand, could becorrelated to the donor–acceptor morphology for the formulations based on the solvents d-limonene,anisole, and 2-methyl anisole, as well as the halogenated reference solvent o-dichlorobenzene. Thisnanostructured blend film morphology was characterised with scanning transmission X-ray microscopy(STXM) and transmission electron microscopy (TEM), and the film surface composition was analysed bynear edge X-ray absorption fine structure (NEXAFS) spectroscopy. Hansen solubility theory, based onsolution thermodynamics, has been used and we propose an HSP-based method that is a general platformfor the rational design of ink formulations for solution-based organic electronics, in particular facilitatingthe green solvent transition of organic photovoltaics. Our results show that the bulk heterojunctionmorphology for a donor–acceptor system processed from customised solvent mixtures can be predictedby the HSP-based method with good reliability.

The film morphology and device performance of planar heterojunction

solar cells based on the molecular donor material α-sexithiophene (6T) are investigated.

Planar heterojunctions of 6T with two different acceptor molecules, the C60 fullerene and

diindenoperylene (DIP), have been prepared. The growth temperature of the 6T bottom

layer has been varied between room temperature and 100 °C for each acceptor. By means

of X-ray diffraction and X-ray absorption, we show that the crystallinity and the molecular

orientation of 6T is influenced by the preparation conditions and that the 6T film

templates the growth of the subsequent acceptor layer. These structural changes are

accompanied by changes in the characteristic parameters of the corresponding

photovoltaic cells. This is most prominently observed as a shift of the open circuit

voltage (Voc): In the case of 6T/C60 heterojunctions, Voc decreases from 0.4 to 0.3 V,

approximately, if the growth temperature of 6T is increased from room temperature to 100

°C. By contrast, Voc increases from about 1.2 V to almost 1.4 V in the case of 6T/DIP solar

cells under the same conditions. We attribute these changes upon substrate heating to

increased recombination in the C60 case while an orientation dependent intermolecular coupling seems to change the origin of the photovoltaic gap in the DIP case.

A polymer vs solvent diagram of film structures, formed in polystyrene (PS) blends (1:1 w:w PS/PT) with poly(3-alkylthiophenes) PT [regioregular R-P3DDT, R-P3HT and regiorandom P3BT, P3DDT] spincoated onto oxidized silicon surfaces from various common solvents [p-xylene, toluene, chloroform, chlorobenzene, cyclohexanone] is presented. The structures were determined with microscopic techniques (atomic, AFM and lateral, LFM, force microscopy, fluorescent microscopy FM) and dynamic secondary ion mass spectrometry (dSIMS). The diagram, arranged according to the solubility parameter of the PTs and the solvents, exhibits three main structural classes: dewetting, lamellar, and lateral (quasi-2-dim) morphology. Decrease in PT solubility parameter δPT inhibits dewetting of polymer films. It induces also a transition from lamellar to lateral film structure. Increase in solvent solubility parameter δS has similar effects. Such behavior is related to the stability of transient homogeneous films and multilayers in the course of spin-casting. The role of δPT and δS is elucidated based on the stability analysis performed in terms of spreading coefficient (dependent on δPT) and effective interfacial tension of solvent-rich polymer phase (dependent on δS).

Spin casting polymer blends of conjugated and dielectric macromolecules onto chemically patterned metal and oxidized silicon surfaces might provide a simple method to fabricate polymer-based circuitries that can be integrated with conventional electronics. Such solution-processing of the blend components offers simultaneous deposition and pattern-directed alignment of the phase separated polymer domains. The alignment is driven by self-organization guided by preferential surface segregation. Here we demonstrate that the laterally arranged domain structures in spin cast films of the

conjugated poly(3-alkylthiophenes) (P3ATs): P3BT, P3DDT and regioregular R-P3HT, blended with dielectric polystyrene (PS), can be ordered by three different surface templates. The templates are formed by a patterned self-assembled monolayer (SAM), micro-contact printed on the surface of interest, i.e. hexadecanethiols on gold (for alignment of P3DDT/PS blend) and octadecyltrichlorosilanes on oxidized silicon (for R-P3HT/PS). Additionally gold lines are micropatterned on SiO2 with photo-lithography (for P3BT/PS mixture). The forces driving pattern-directed self-organization of the polymers are discussed based on complementary studies of preferential surface segregation, observed for blend films spin cast on homogeneous surfaces that correspond to the different regions of the surface templates

We report a comparison of the work functions of thin films of indium tin oxide (ITO), carried out by means of ultraviolet photoelectron spectroscopy (UPS) and by measurements of the contact potential difference with respect to a gold reference electrode (Kelvin probe (KP) method). We investigated commercially available ITOs both "as-received", and after certain surface treatments, such as oxygen plasma. First, we find measurable discrepancies between KP values measured with three different instruments, and between the KP and the UPS values. Secondly, and unexpectedly, we find that the KP, although more sensitive than UPS, does not detect certain differences between ITOs with different surface treatments. We discuss the results in view of the different environments in which the measurements are carried out (UHV for the UPS and air/Ar for the Kelvin method), of the effects which may be induced by the high-energy photon irradiation in the UPS measurement, and of the stability of the gold probe work function in gas ambient. We conclude that UPS is better-suited for absolute work function determination, although KP remains a convenient and inexpensive tool for fast screening of contact potential differences. (C) 2000 Elsevier Science S.A. All rights reserved.

Purposes of employing barrier coatings in packaging, and in particular food packaging, can be to increase the shelf life, preserve colour, odour, and taste, and to protect from a harmful environment in general. Barrier coatings can thus help to reduce food waste along the value chain until end use. Including both materials choice for packaging and the possible fates of the used package, even further steps to provide greater knowledge for decisions on choices of packaging solutions. To that end, we have conducted several experimental and transport modeling studies on oxygen barrier coatings performance. The coating system of choice    has been dispersion coatings of poly vinyl alcohol (PVOH), with additions of kaolin. Physical and chemical features of the coatings were characterized to obtain information on polymer crystallinity, free volume and filler orientation as these characteristics are influential to the oxygen mass transport performance. In turn, the oxygen mass transport was also measured, both in steady state and dynamically. In so doing, we obtained information    useful for developing a general model to describe the oxygen permeability taking into account the physical and chemical features, described above, of the coating layer. Attempts on describing the interdependence and impact, for instance between crystalline and amorphous polymer regions and moisture, was added to the model. The model showed agreement to experimental data for PVOH-kaolin coating in this particular case. However, the basic permeability model has been applied to  many different polymers.

To further explore the potential of these types of coating, which are technically possible to    produce in paperboard production, an economic-environmental impact comparison to other existing material solutions was made. Four barrier material alternatives – starch, polyethylene, ethyl vinyl alcohol (chosen as an alternative for PVOH, where data was difficult to obtain) and kaolin, and latex and kaolin, were analyzed with respect to cost and global warming potential. Weighting and comparing cost to environmental aspect, weighting    factors based on interviews with experts in the packaging value chain, starch emerges as the most sustainable alternative. However, previous coating and mass transport studies also shows how these renewable materials require some further technical development to be competitive.

The mass transport model can serve as a tool for customizing barrier coatings and to predict the barrier performance, as permeability is obtained and thus shelf-life estimation is    possible. The overall concept, the combination of assessment of structural performance and the environmental studies, can be employed to find sustainable food packaging solutions.

We report on the effects of the film morphology on the fluorescence spectra for a thin film including a quinoxaline-based co-polymer (TQ1) and a fullerene derivative ([6,6]-phenyl-C71-butyric acid methyl ester-PC70BM). The ratio between the polymer and the fullerene derivative, as well as the processing solvent, were varied. Besides the main emission peak at 700 nm in the fluorescence spectra of thin films of this phase-separated blend, a broad emission band is observed with a maximum at 520-550 nm. The intensity of this emission band decreases with an increasing degree of mixing in the film and becomes most prominent in thicker films, films with high PC70BM content, and films that were spin-coated from solvents with lower PC70BM solubility. We assign this emission band to aggregated PC70BM.

The formation of the surface-induced stratified lamellar composition profile experimentally evidenced in spincoated layers of the photovoltaic donor–acceptor blend consisting of poly[(9,9-dioctylfluorenyl-2,7-diyl)-co-5,5-(4′,7′-di-2-thienyl-2′,1′,3′-benzothiadiazole]/phenyl-C61-butyric acid methyl ester (APFO-3/PCBM), as processed from chloroform, is simulated using square gradient theory extended with terms describing the interaction of the blend components with the air and substrate interfaces. The surface energy contributions have been formulated based on an enthalpic nearest-neighbor model which allows integration of common surface tension theory and experimentally accessible surface energies of the fluid phase constituents with a mean field description of a multicomponent blend confined by substrate and air interfaces. Using estimates for the quench depth and transport properties of the blend components as a function of polymer concentration, the time-resolved numerical simulations yield results that compare favorably with experimental observations, both in terms of the number of lamellae as a function of the blend layer thickness and their compositional order. The effect of blend ratio is reproduced as well, the lamellar pattern becoming more pronounced if the amount of PCBM increases relative to APFO-3.

The performance and recent improvements of polymer-based solar cells can be traced back

to two main factors: the chemical design of new conjugated polymers and the control and

improved understanding of morphology in these solution-processed thin films. When a thin

film is prepared from a blend of a conjugated polymer and the fullerene-based material,

PCBM, demixing determines the final nanostructure, which in turn is influenced by the

polymer-fullerene interactions, the molecules’ tendency to self-organise, and the kinetics of

the film formation. During spincoating, characterized of rapid solvent evaporation, the

kinetics of nucleation and of two-phase separation compete. The resulting film morphology

is important for the performance of photovoltaic devices, because, first of all, excitons need

to diffuse to the donor/acceptor interface to separate into mobile charges, and, secondly,

these mobile charges need to travel to the electrodes. Characterization of the structure,

composition and molecular orientation at these interfaces and in the thin film has been one

major challenge, because of the critical requirements of chemical contrast combined with

lateral or depth resolution. We have used a combination of Atomic Force Microscopy

(AFM), dynamic Secondary Ion Mass Spectrometry (d-SIMS), Near-Edge Absorption Fine

Structure (NEXAFS) spectroscopy, and recently Neutron Reflectometry (NR), to probe the

surface and bulk composition of polymer:fullerene blends. Differences in composition

between surface and sub-surface are observed, and form strong evidence for vertical phase

separation.

Polymer/fullerene solar cells with three different device structures: A) diffuse bilayer, B) spontaneously formed multilayer, and C) vertically homogenous thin films, are fabricated. The photocurrent/voltage performance is compared and it is found that the self-stratified structure (B) yields the highest energy conversion efficiency

The thermal behaviour of an organic photovoltaic (OPV) binary system comprised of a liquidcrystalline fluorene-based polymer and a fullerene derivative is investigated. We employ variabletemperature ellipsometry complemented by photo- and electroluminescence spectroscopy as well as optical microscopy and scanning force nanoscopy to explore phase transitions of blend thin films. The high glass transition temperature correlates with the good thermal stability of solar cells based on these materials. Furthermore, we observe partial miscibility of the donor and acceptor together with the tendency of excess fullerene derivative to segregate into exceedingly large domains. Thus, for charge generation less adequate bulk-heterojunction nanostructures are poised to develop if this mixture is exposed to more elevated temperatures. Gratifyingly, the solubility of the fullerene derivative in the polymer phase is found to decrease if a higher molecular-weight polymer fraction is employed, which offers routes towards improving the photovoltaic performance of non-crystalline OPV blends.

Fully conjugated organic molecules, such as the oligo(phenyleneethynylene) (OPE) systems, are of growing interest within the field of molecular electronics, as is the self-assembly of well-defined molecular thin films with predefined functions. The structure and function of such films are intimately related and governed by the structures of their molecular constituents, through the intermolecular interactions and the interactions between the molecules and the substrate, onto which the film is assembled. Here we report on the synthesis of a series of three OPE derivatives, with the general structure phenylethynylene−aryl−ethynylenephenylene−headgroup, and the structural investigation of the self-assembled monolayers (SAMs) formed from them on Au(111) surfaces. The SAMs were characterized by infrared reflection−absorption spectroscopy, spectroscopic ellipsometry, high-resolution X-ray photoemission spectroscopy, and near-edge X-ray absorption fine structure spectroscopy. The effective thickness of the SAMs was observed to decrease as the π-system of the aryl moiety of the OPE adsorbate was extended perpendicular to its molecular long axis. Changing the aryl moiety from benzene to naphthalene to anthracene resulted in lower molecular surface densities and larger molecular inclination. The average tilt angles for the benzene, naphthalene, and anthracene SAMs were found to be about 30°, 40°, and 42° from the surface normal, respectively. For the largest adsorbate, the anthracene derivative, there is spectroscopic evidence suggesting the existence of nonequivalent binding sites. The differences observed between the SAMs are rationalized in terms of the shape of the adsorbates and the strength of the π−π interactions between them

In this study the morphology of spin-casted films of polymers blended with [6,6]-phenyl C₆₁-butyric acid methyl ester (PCBM) has been studied. It was found that the lateral structure formation in the films is favored by rapid solvent evaporation and strong polymer−PCBM repulsion. The formation of homogeneous films is favored by slow evaporation and weak polymer−PCBM repulsion. The effect of solvent evaporation rate is the opposite of what is found for spin-casting polymer−polymer blends. The results can be explained by the kinetics of phase separation and the phase behavior involving limited solubility and crystallization of PCBM.

The permeability of dispersion barriers produced from polyvinyl alcohol (PVOH) and kaolin clay blends coated onto polymeric supports has been studied by employing two different measurement methods: the oxygen transmission rate (OTR) and the ambient oxygen ingress rate (AOIR). Coatings with different thicknesses and kaolin contents were studied. Structural information of the dispersion-barrier coatings was obtained by Fourier transform infrared spectroscopy (FTIR) spectroscopy and scanning electron microscopy (SEM). These results showed that the kaolin content influences both the orientation of the kaolin and the degree of crystallinity of the PVOH coating. Increased kaolin content increased the alignment of the kaolin platelets to the basal plane of the coating. Higher kaolin content was accompanied by higher degree of crystallinity of the PVOH. The barrier thickness proved to be less important in the early stages of the mass transport process, whereas it had a significant influence on the steady-state permeability. The results from this study demonstrate the need for better understanding of how permeability is influenced by (chemical and physical) structure.

This paper presents a study of the effect of moisture on the gas permeability of polyvinyl alcohol (PVOH) and PVOH–kaolin dispersion barrier coatings. The oxygen permeability was measured at different humidity levels, and the material properties were characterized under the same conditions: polymer crystallinity, kaolin concentration, and kaolin orientation were all evaluated. The experimental results revealed that the water plasticizes the PVOH material of the coatings, and the presence of kaolin filler is unable to affect such behavior significantly. The PVOH crystallinity was affected drastically by the humidity, as water melts polymer crystallites, which is a reversible process under removal of water. The permeability data were analyzed using a thermodynamicbased model able to account for the water effect on both the solubility of the gas and the diffusivity coefficients in the polymer and composite. The results showed good agreement between the model’s predictions and the experimental data in terms of the overall permeability of the material.

In this study oxygen permeability in dispersion barriers produced from poly(vinyl alcohol) (PVOH) and kaolin clay blends coated onto polymeric supports was investigated. To determine the oxygen permeability, two measurement methods were used: the oxygen transmission rate (OTR) and the ambient oxygen ingress rate (AOIR). It was found that with increasing kaolin content the oxygen permeability increased, up to about 5 wt% kaolin, whereafter the oxygen permeability decreased, as was expected. The increased (> 5%) kaolin loading lowered the diffusion because of an increased tortuosity. Structural information about the dispersion-barrier coatings, such as kaolin orientation and polymer crystallinity, was obtained from Fourier transform infrared spectroscopy (FTIR) and scanning electron microscopy (SEM). Kaolin orientation was influenced by the drying temperature, the thickness of the samples, and the kaolin concentration. The polymer crystallinity increased in thicker samples. The drying temperature did not show any clear effect on the crystallinity of thin samples, while for the thicker barriers, combined with a kaolin concentration lower than 20 wt%, a higher crystallinity was achieved at lower drying temperatures. This study demonstrates the strong influence of chemical and physical structures on the permeability of the investigated coatings.

We reveal the rather complex interplay of contact-induced re-orientation and interfacial electronic structure-in the presence of Fermi-level pinning-at prototypical molecular heterojunctions comprising copper phthalocyanine (H16CuPc) and its perfluorinated analogue (F16CuPc), by employing ultraviolet photoelectron and X-ray absorption spectroscopy. For both layer sequences, we find that Fermi-level (E-F) pinning of the first layer on the conductive polymer substrate modifies the work function encountered by the second layer such that it also becomes E-F-pinned, however, at the interface towards the first molecular layer. This results in a charge transfer accompanied by a sheet charge density at the organic/organic interface. While molecules in the bulk of the films exhibit upright orientation, contact formation at the heterojunction results in an interfacial bilayer with lying and co-facial orientation. This interfacial layer is not EF-pinned, but provides for an additional density of states at the interface that is not present in the bulk. With reliable knowledge of the organic heterojunction's electronic structure we can explain the poor performance of these in photovoltaic cells as well as their valuable function as charge generation layer in electronic devices.

Self-organization of liquid crystalline and crystalline-conjugated materials has been used to create, directly from solution, thin films with structures optimized for use in photodiodes. The discotic liquid crystal hexa-perihexabenzocoronene was used in combination with a perylene dye to produce thin films with vertically segregated perylene and hexabenzocoronene, with large interfacial surface area. When incorporated into diode structures, these films show photovoltaic response with external quantum efficiencies of more than 34 percent near 490 nanometers. These efficiencies result from efficient photoinduced charge transfer between the hexabenzocoronene and perylene, as well as from effective transport of charges through vertically segregated perylene and hexabenzocoronene psystems. This development demonstrates that complex structures can be engineered from novel materials by means of simple solution-processing steps and may enable inexpensive, high-performance, thin-film photovoltaic technology

The reactions of coronene dehydrogenation and fusion upon heat treatment in the temperature range of 500700 C were studied using XRD, TEM, Raman, IR, and NEXAFS spectroscopy. The formation of a coronene dimer (dicoronylene) was observed at temperatures 530-550 C; dicoronylene can easily be separated using sublimation with a temperature gradient. An insoluble and not sublimable black precipitate was found to form at higher temperatures. Analysis of the data shows that dimerization of coronene is followed at 550600 C by oligomerization into larger molecules. Above 600 C amorphization of the material and formation of graphitic nanoparticles was observed. Coronene fusion by annealing is proposed as a road to synthesis of larger polycyclic aromatic hydrocarbons and nanographenes.

Graphite oxides synthesized by one and two step Brodie oxidation (BGO) and Hummers (HGO) methods were analyzed by a variety of characterization methods in order to evaluate the reasons behind the difference in their properties. It is found that the Brodie method results in a higher relative amount of hydroxyl groups and a more homogeneous overall distribution of functional groups over the planar surface of the graphene oxide flakes. The higher number of carbonyl and carboxyl groups in HGO, detected by several methods, including XPS, NMR and FTIR, unavoidably results in defects of the graphene "skeleton", holes and overall disruption of the carbon-carbon bond network, stronger deviation from planar flake shape and poor ordering of the graphene oxide layers. It is also suggested that functional groups in HGO are less homogeneously distributed over the flake surface, forming some nanometer-sized graphene areas. The presence of differently oxidized areas on the GO surface results in inhomogeneous solvation and hydration of HGO and effects of inter- and intra-stratification. The proposed interpretation of the data explains the higher mechanical strength of multi-layered BGO membranes/papers, which are also less affected by humidity changes, thus providing an example of a membrane property superior to that of HGO. (C) 2016 Published by Elsevier Ltd.

Blend thin films, prepared by dip-coating, of polyfluorene (F8 or PFO), acting as an electron donor, and [6,6]-phenyl-C-61-butyric acid methyl ester (PC60BM), acting as the electron acceptor, have been characterized by UV/VIS absorption spectroscopy, static and dynamic fluorescence, and atomic force microscopy. Four different solvents were used for the film preparation; the monohalogenated fluorobenzene and chlorobenzene and their dihalogenated counterparts o-difluorobenzene and o-dichlorobenzene, respectively. Fluid mechanics calculations were used to determine the withdrawal speed for each solvent, in order to prepare wet films of comparable thicknesses. The resulting dry films were also of similar thicknesses. It was found that the choice of solvent influences the ability for F8 to form its beta-phase.

The stability of organic solar cells (OSCs) is critical for practical applications of this emerging technology. Unfortunately, in spite of intensive investigations, the degradation mechanisms in OSCs have not been clearly understood yet. In this report, we employ a range of spectroscopic and transport measurements, coupled with drift-diffusion modelling, to investigate the light-induced degradation mechanisms of fullerene-based OSCs. We find that trap states formed in the fullerene phase under illumination play a critical role in the degradation of the open-circuit voltage (V-OC) in OSCs. Our results indicate that the degradation is intrinsic to the fullerenes in OSCs and that alternative acceptor materials are desired for the development of stable OSCs.

Mixed self-assembled monolayers of 11-ferrocene-1-undecanethiol (FcC11) and decanethiol (C10) were prepared by two different methods: from a mixed solution and by subsequent immersion. These preparations result in self-assembled monolayers (SAMs) with different portions of FcC11 molecules, orientations, and degrees of order in the SAM. The structure of these layers was studied by high-resolution X-ray photoelectron spectroscopy (HRXPS) and near-edge X-ray absorption fine structure (NEXAFS) spectroscopy, and their effect on the surface electronic properties was investigated by Kelvin probe. The fraction of FcC11 in C10 thiol could be estimated from the intensity of the HRXPS Fe 2p3/2 peaks. The SAM prepared from the mixed solution was of high quality, and the portion of FcC11 molecules in this film was about 60%. The interaction of neighboring ferrocene moieties indicated phase separation between FcC11 and C10 species in the film. For the SAMs prepared by subsequent immersion in C10 and FcC11 solutions, the portion of FcC11 molecules varied from 35% to 55% dependent on the immersion times in the C10 solution. The degree of orientational order of the alkyl chains increased with increasing immersion time in C10. In addition, the adsorption of C10 decreased the work function of the gold surface while the adsorption of FcC11 increased this value. By varying the fraction of FcC11 in the SAMs with different preparation schemes, the work function of the gold surface could be varied in a controllable way

Porphyrin-functionalized oligo(phenyleneethynylene)s (OPE) are promising molecules for molecular electronics applications. Three such molecules (1-3) with the common structure P-OPE-AG (P and AG are a porphyrin and anchor group, respectively) and different anchor groups, viz. an acetyl protected thiol, -S-COCH3 (1), an acetyl protected thiol with methylene linker, -CH2-S-COCH3 (2), and a trimethylsilylethynyl group, -C(triple bond)C-Si(CH3)3 (3) have been synthesized and the corresponding self-assembled monolayers (SAMs) on Au(111) substrates have been prepared. The integrity and structural properties of these films were studied by X-ray photoelectron spectroscopy and near-edge X-ray absorption fine structure spectroscopy. The results suggest that the films formed from 1 have a high orientational order with an almost upright orientation and dense packing of the molecular constituents, i.e. represent a high quality SAM. In contrast, molecule 2 formed disordered molecular layers on Au, even though the molecule-surface bonding (thiolate) is the same as in the case of molecule 1. This suggests that the methylene linker in molecule 2 has a strong impact on the quality of the resulting film, so that a well-ordered SAM cannot be formed. The silane system, 3, is also able to bind to the gold surface but the resulting SAM has a poor quality, being significantly disordered and/or comprised of strongly inclined molecules. The above results suggest that the nature of the anchor group along with a possible linker is an important parameter which, to a high extent, predetermines the entire quality of OPE-based molecular layers