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Molecular doping is a key process to increase the density of charge carriers in organic semiconductors. Doping induced charges in polymer semiconductors result in the formation of polarons and or bipolarons due to the strong electron vibron coupling in conjugated organic materials. Identifying the nature of charge carriers in doped polymers is essential to optimize the doping process for applications. In this work, we use Raman spectroscopy to investigate the formation of charge carriers in molecularly doped poly 3 hexylthiophene 2,5 diyl P3HT for increasing dopant concentration, with the organic salt dimesityl borinium tetrakis penta fluorophenyl borate Mes2B [B C6F5 4] amp; 8722; and the Lewis acid tris pentafluorophenyl borane [B C6F5 3]. While the Raman signatures of neutral P3HT and singly charged P3HT segments polarons are known, the Raman spectra of doubly charged P3HT segments bipolarons are not yet sufficiently understood. Combining Raman spectroscopy measurements on doped P3HT thin films with first principles calculations on oligomer models, we explain the evolution of the Raman spectra from neutral P3HT to increasingly doped P3HT featuring polarons and eventually bipolarons at high doping levels. We identify and explain the origin of the spectral features related to bipolarons by tracing the Raman signature of the symmetric collective vibrations along the polymer backbone, which compared to neutral P3HT redshifts for polarons and blueshifts for bipolarons. This is explained by a planarization of the singly charged P3HT segments with polarons and rather high order in thin films, while the doubly charged segments with bipolarons are located in comparably disordered regions of the P3HT film due to the high dopant concentration. Furthermore, we identify additional Raman peaks associated with vibrations in the quinoid doubly charged segments of the polymer. Our results offer the opportunity for readily identifying the nature of charge carriers in molecularly doped P3HT while taking advantage of the simplicity, versatility, and non destructive nature of Raman spectroscopy

In this study, the kinetics of the adsorption of 2,3,5,6 tetrafluoro 7,7,8,8 tetracyanoquinodimethane F4TCNQ on the surface of Ag nanoparticles Ag NPs in chloroform has been intensively investigated, as molecular doping is known to play a crucial role in organic electronic devices. Based on the results obtained from UV visible vis near infrared NIR absorption spectroscopy, cryogenic transmission electron microscopy, scanning nanobeam electron diffraction, and electron energy loss spectroscopy, a two step interaction kinetics has been proposed for the Ag NPs and F4TCNQ molecules, which includes the first step of electron transfer from Ag NPs to F4TCNQ indicated by the ionization of F4TCNQ and the second step of the formation of a Ag F4TCNQ complex. The whole process has been followed via UV vis NIR absorption spectroscopy, which reveals distinct kinetics at two stages the instantaneous ionization and the long term complex formation. The kinetics and the influence of the molar ratio of Ag NPs F4TCNQ molecules on the interaction between Ag NPs and F4TCNQ molecules in an organic solution are reported herein for the first time. Furthermore, the control experiment with silica coated Ag NPs manifests that the charge transfer at the surface between Ag NPs and F4TCNQ molecules is prohibited by a silica layer of 18 nm

Previous research has shown that orthographic marking may have a function beyond identifying orthographic word forms. In two visual priming experiments with native speakers and advanced learners of German (Czech natives) we tested the hypothesis that orthography can convey word-class cues comparable to morphological marking. We examined the effect of initial letter capitalization of nouns (a specific property of German orthography) on the processing of five homonymous and grammatically ambiguous forms. Both populations showed the same pattern of results: deverbal nouns (conversions) patterned together with countable nouns while in a previous study (with eliminated orthographic word-class cues) they patterned together with infinitives. Together, findings suggest that orthographic cues can trigger word-class-specific lexical retrieval/access. They also suggest a lexical entry structure in which conversion nouns, infinitives, and inflected verbal forms share a category-neutral parent node and that specified subnodes are accessed only when specifying cues are available and/or necessary for processing.

In two visual priming experiments, we investigated the relation of form-identical word forms with different grammatical functions in L1 and L2 German. Four different grammatical types (inflected verbs, infinitives, deverbal conversion forms, and countable nouns) were used as primes and their influence on the processing of form-identical inflected verbs as targets was compared. Results revealed full priming of inflected verbs, but only partial priming for conversion forms and infinitives. No priming was observed for semantically related countable nouns suggesting that they have a separate lexical entry. The findings bring first psycholinguistic evidence for typological claims that deverbal conversion nouns and infinitives fall into the category of nonfinites. They also support accounts assuming representations with a basic lexical entry and word-category specific subentries. The same priming pattern was observed in L1 and L2 suggesting that representation and processing of the studied complex forms is not fundamentally different in the two populations.

We introduce the blueprint of the Ontogenesis Model of the L2 Lexical Representation (OM) that focuses on the development of lexical representations. The OM has three dimensions: linguistic domains (phonological, orthographic, and semantic), mappings between domains, and networks of lexical representations. The model assumes that fuzziness is a pervasive property of the L2 lexicon: most L2 lexical representations are low resolution and the ontogenetic curve of their development does not reach the optimum (i.e., the ultimate stage of their attainment with optimal encoding) in one or more dimensions. We review the findings on lexical processing and vocabulary training to show that the OM has a potential to provide an interpretation for the results that have been treated separately and to move us forward in building a comprehensive model of L2 lexical acquisition and processing.

In the present study we challenge the generally accepted view based primarily on L1 data that surface linguistic information decays rapidly during reading and that only propositional information is retained in memory. In two eye-tracking experiments, we show that both L1 and L2 adult readers retain verbatim information of a text. In particular, the reading behaviour of L2 German learners revealed that they were sensitive to both lexical (synonyms) and syntactic (active/passive alternation) substitutions during a second reading of the texts, while L1 exhibited only reduced sensitivity to the lexical substitutions. The results deliver an important piece of evidence that complies with several current processing (e.g., Shallow Structure Hypothesis), acquisition (Declarative/Procedural Model) and cognitive (e.g., Fuzzy Trace Theory) approaches and adds a new dimension to their empirical and theoretical basis.

Optical absorption spectroscopy is a key method to investigate doped conjugated polymers and to characterize the doping-induced charge carriers, i.e., polarons. For prototypical poly(3-hexylthiophene-2,5-diyl) (P3HT), the absorption intensity of molecular dopant induced polarons is widely used to estimate the carrier density and the doping efficiency, i.e., the number of polarons formed per dopant molecule. However, the dependence of the polaron-related absorption features on the structure of doped P3HT, being either aggregates or separated individual chains, is not comprehensively understood in contrast to the optical absorption features of neutral P3HT. In this work, we unambiguously differentiate the optical signatures of polarons on individual P3HT chains and aggregates in solution, notably the latter exhibiting the same shape as aggregates in solid thin films. This is enabled by employing tris(pentafluorophenyl)borane (BCF) as dopant, as this dopant forms only ion pairs with P3HT and no charge transfer complexes, and BCF and its anion have no absorption in the spectral region of P3HT polarons. Polarons on individual chains exhibit absorption peaks at 1.5 eV and 0.6 eV, whereas in aggregates the high-energy peak is split into a doublet 1.3 eV and 1.65 eV, and the low-energy peak is shifted below 0.5 eV. The dependence of the fraction of solvated individual chains versus aggregates on absolute solution concentration, dopant concentration, and temperature is elucidated, and we find that aggregates predominate in solution under commonly used processing conditions. Aggregates in BCF-doped P3HT solution can be effectively removed upon simple filtering. From varying the filter pore size (down to 200 nm) and thin film morphology characterization with scanning force microscopy we reveal the aggregates' size dependence on solution absolute concentration and dopant concentration. Furthermore, X-ray photoelectron spectroscopy shows that the dopant loading in aggregates is higher than for individual P3HT chains. The results of this study help understanding the impact of solution pre-aggregation on thin film properties of molecularly doped P3HT, and highlight the importance of considering such aggregation for other doped conjugated polymers in general.

Background and Aims: Only little is known about blood groups other than ABO blood groups and Rhesus factors in Arabian countries and Iran. During the last years, increased migration to Central Europe has put a focus on the question how to guarantee blood supply for patients from these countries, particularly because hemoglobinopathies with the need of regular blood support are more frequent in patients from that region. Therefore, blood group allele frequencies should be determined in individuals from Arabian countries and Iran by molecular typing and compared to a German rare donor panel. Methods: 1,111 samples including 800 individuals from Syria, 147 from Iran, 123 from the Arabian Peninsula, and 41 from Northern African countries were included in a MALDI-TOF MS assay to detect polymorphisms coding for Kk, Fy(a/b), Fynull, Cw, Jk(a/b), Jo(a+/a–), Lu(a/b), Lu(8/14), Ss, Do(a/b), Co(a/b), In(a/b), Js(a/b), Kp(a/b), and variant alleles RHCE*c.697C>G and RHCE*c.733C>G. Yt(a/b), S–s–U–, Velnull, Conull, and RHCE*c.667G>T were tested by PCR-SSP. Results: Of the Arabian donors, 2% were homozygous for the FY*02.01N allele (Fynull), and 15.7% carried the heterozygous mutation. However, 0.8% of the German donors also carried 1 copy of the allele. 3.6% of all and 29.3% of Northern African donors were heterozygous for the RHCE*c.733C>G substitution, 0.4% of the Syrian probands were heterozygous for DO*01/DO*01.-05, a genotype that was lacking in German donors. Whereas the KEL*02.06 allele coding for the Js(a) phenotype was missing in Germans; 0.8% of the Syrian donors carried 1 copy of this allele. 1.8% of the Syrian but only 0.3% of the German donors were negative for YT*01. One donor from Northern Africa homo­zygously carried the GYPB*270+5g>tmutation, inducing the S–s–U+w phenotype, and in 2 German donors a GYPB*c.161G>A exchange, which induces the Mit+ phenotype, caused a GYPB*03 allele dropout in the MALDI assay. The overall failure rate of the Arabian panel was 0.4%. Conclusions: Some blood group alleles that are largely lacking in Europeans but had been described in African individuals are present in Arabian populations at a somewhat lower frequency. In single cases, it could be challenging to provide immunized Arabian patients with compatible blood.

Surface-defect passivation is key to achieving high photoluminescence quantum yield in lead halide perovskite nanocrystals. However, in perovskite light-emitting diodes these surface ligands also have to enable balanced charge injection into the nanocrystals to yield high efficiency and operational lifetime. In this respect, alkaline halides have been reported to passivate surface trap states and increase the overall stability of perovskite light emitters. On the one side, the incorporation of alkaline ions into the lead halide perovskite crystal structure is considered to counterbalance cation vacancies, while, on the other side, the excess halides are believed to stabilise the colloids. Here, we report an organic lithium salt, viz. LiTFSI, as a halide-free surface passivation on perovskite nanocrystals. We show that the treatment LiTFSI has multiple beneficial effects on lead halide perovskite nanocrystals and LEDs derived from them. We obtain higher photoluminescence quantum yield and longer exciton lifetime, and a radiation pattern that is more favourable for light outcoupling. The ligand-induced dipoles on the nanocrystal surface shift their energy levels toward lower hole-injection barrier. Overall, these effects add up to a four- to seven-fold boost of the external quantum efficiency in proof-of-concept LED structures, depending on the color of the used lead halide perovskite nanocrystal emitters., Comment: 42 pages

In the quest towards more durable solution-processed solar cells, the stability of the active layer materials under operation conditions is important. While lifetimes of several years have been demonstrated for encapsulated organic solar cells, it is generally known that degradation events can be accounted for by air components (O2 and/or water vapour) leaking into the cell through a non-ideal sealing. Here we present a fundamental study of intentional photo-degradation of the electron-acceptor PC60BM ([6,6]-phenyl-C61-butyric acid methyl ester) in air, with the purpose of improving the understanding of the electronic effects of fullerene photo-oxidation. We have studied spincoated thin films of PC60BM by X-ray Photoelectron Spectroscopy, Near-edge X-ray Absorption Fine Structure spectroscopy, and Fourier Transform Infrared Spectroscopy, before and after exposing them to simulated sunlight in air. The changes observed in the spectra obtained by these complementary methods were compared with calculated spectra of a large set of possible oxidation products of PC60BM where oxygen atoms have been attached to the C60 cage. The best fit with experimental IR spectra of photodegraded PC60BM films was obtained for a linear combination of calculated spectra for two degradation products, a dicarbonyl and an anhydride, both with open cages with 58 carbon atoms, and the pristine PC60BM molecule. From this comparison, we conclude that the conjugation of the fullerene cage is disturbed by the formation of several carbonyl-based derivatives on the C60 cage, accompanied by a transition from sp2 to sp3-hybridized carbon. The π* resonance in the C1s NEXAFS spectrum was found to be a very sensitive probe for small changes to the fullerene cage, and FT-IR was needed in combination with O1s NEXAFS, to identify the oxidation products. Article part of Blazinic's (2019) doctoral thesis Probing the effects of photodegradation of acceptor materials in polymer solar cells: bulk, surface, and molecular level as manuscript.

The study explores the degree to which readers can use their previous linguistic knowledge, which goes beyond the immediate evidence in the input, to create mental representations of new words and how the employment of this knowledge may reduce the fuzziness of the new representations. Using self-paced reading, initial representations of novel identical forms with different grammatical functions were compared in native German speakers and advanced L2 German learners with L1 Czech. The results reveal that although both groups can employ general knowledge about German grammar when establishing new representations, the L1 native speakers outperform the L2 learners: Their new representations have more precise structure and are better differentiated from related representations with respect to their grammatical information. Modeling consequences of these findings are discussed in the context of the Ontogenesis Model of the L2 Lexical Representation and the Fuzzy Lexical Representation Hypothesis.

Doping the electron transport polymer poly [N,N amp; 8242; bis 2 octyldodecyl naphthalene 1,4,5,8 bis dicarboximide 2,6 diyl] alt 5,5 amp; 8242; 2,2 amp; 8242; bithiophene [P NDI2OD T2 ] with the bulky, strongly reducing metallocene 1,2,3,4,1 amp; 8242;,2 amp; 8242;,3 amp; 8242;,4 amp; 8242; octaphenylrhodocene OPR leads to an increased bulk conductivity and a decreased contact resistance. While the former arises from low level n doping of the intrinsic polymer and increased carrier mobility due to trap filling, the latter arises from a pronounced accumulation of dopant molecules at an indium tin oxide ITO substrate. Electron transfer from OPR to ITO leads to a work function reduction, which pins the Fermi level at the P NDI2OD T2 conduction band and thus minimizes the electron injection barrier and the contact resistance. The results demonstrate that disentangling the effects of electrode modification by the dopant and bulk doping is essential to comprehensively understand doped organic semiconductors

Im vorliegenden Beitrag identifizieren wir Möglichkeiten und Grenzen einer Aufarbeitung bisher noch ungenutzter Datenquellen für raum-zeitliche Biodiversitätsanalysen in Deutschland. Im Rahmen des Syntheseprojekts sMon (https://www.idiv.de/smon) des Deutschen Zentrums für integrative Biodiversitätsforschung (iDiv) Halle-Jena-Leipzig erprobt eine Arbeitsgemeinschaft aus Bundes- und Landesbehörden gemeinsam mit Fachgesellschaften, Verbänden und wissenschaftlichen Einrichtungen Methoden, wie heterogene Daten der letzten Jahrzehnte für retrospektive Trendanalysen genutzt werden können. Darauf aufbauend schlagen wir gangbare Wege zur Zukunft des deutschen Biodiversitätsmonitorings vor und illustrieren, wie Daten aus der Vergangenheit helfen können, Monitoring künftig zu gestalten.

Background: The federal state of Saarland (SL) is experiencing the fastest demographic change in the western part of Germany. In this study, we analyzed retrospective data on the current and future supply of red blood cell concentrates (RBC) in this region and compared it to the current and future RBC demand in SL hospitals. Methods: The projection of the SL blood supply in 2030 was modeled based on SL demographics for age distribution and donation frequency of donors, and the RBC transfusion data for in-house patients. These results were compared to published data on the transfusion demand from the state of Mecklenburg-Western Pomerania (MV). Results: For the period January 1 to December 31, 2017, a total of 43,205 whole blood donations were collected. The donation frequency in SL never exceeded 80 per 1,000 inhabitants and was well below the numbers in MV. Thirty-one percent of the donors were responsible for 53.5% of the donations, and donors older than 45 years of age contributed highly to the total blood supply. In addition, 40,614 RBC transfusions at 10 SL hospitals were analyzed representing nearly all RBC transfusions for in-house patients in this region. RBC transfusions per 1,000 inhabitants increased with age from 24 (50–54) to 140 (80–84) years. Facing an already existing structural deficit of nearly 8,200 RBC in 2017, the projection predicts a dramatic increase in the regional deficit to >18,300 RBC in 2030. Conclusion: Our results on RBC demand in SL are comparable but not identical to those projected for the region of MV in eastern Germany. Due to the ongoing demographic changes in Germany as a whole, regular regional monitoring of RBC demand and the age structure of blood recipients and donors should be implemented to allow for better strategic planning in blood transfusion services and hospitals.

Increased hole density in an electron donor-type organic semiconductor can be achieved by deposition of a strong acceptor-type molecular layer on top, and has been shown to enable adjusting the carrier density in organic field effect transistors (OFETs). This interfacial charge transfer is due to simultaneous Fermi level (EF) pinning of the donor's highest occupied level and the acceptor's lowest unoccupied level. Here, we investigate the electrical properties of such an EF-pinned junction formed by diindenoperylene (DIP, as donor) and hexafluoro-tetracyano-naphthoquinodimethane (F6, as acceptor) in OFETs, as well as its electronic properties by photoelectron spectroscopy and electrostatic modelling. We find that, in addition to the EF-pinning induced integer charge transfer across the interface, DIP and F6 form charge transfer complexes (CPXs) at their junction. The molecularly thin CPX interlayer acts as insulator and significantly reduces the density of carriers induced on either side of the junction, compared to a scenario without such an interlayer. CPX formation is thus unfavourable for the effectiveness of controlling carrier density at molecular donor/acceptor junctions by EF-pinning.

Tuning the energy levels of organic semiconductors in a predictable and durable manner is a challenging, yet necessary task to obtain high performance electronic and optoelectronic devices. Thermal diffusion and drift of dopants used for energy level control in the mostly van der Waals-cohered solids results in the degradation of the defined interfaces that all electronic and optoelectronic devices rely on. An important goal is therefore their spatial fixation in multilayer organic device stacks. This work aims at covalently functionalizing the interface of an immobilized organic semiconductor polymer. To achieve this goal, the side chains of a polyfluorene are equipped with biscyclopentadienyl moieties which undergo thermal fragmentation via retro-Diels–Alder reactions to yield cyclopentadienyl functions. Diels–Alder cycloadditions of these functional groups cross-link adjacent polymer chains. In a second step, unreacted cyclopentadienyl units at the interface are covalently functionalized with strong dienophiles through a Diels–Alder reaction from solution. This reaction sequence modifies the energetics and the work function at the interface. Transfer of our protocol to other conjugated polymers and/or reaction types paves the way to tunable energy levels at organic–organic interfaces and to universal introduction of functions at organic semiconductor interfaces after deposition from solution.

The use of polyethylenimine (PEI) as a thin interlayer between cathodes and organic semiconductors in order to reduce interfacial Ohmic losses has become an important approach in organic electronics. It has also been shown that such interlayers can form spontaneously because of vertical phase separation when spin-coating a blended solution of PEI and the semiconductor. Furthermore, bulk doping of semiconducting polymers by PEI has been claimed. However, to our knowledge, a clear delineation of interfacial from bulk effects has not been published. Here, we report a study on thin films formed by spin-coating blended solutions of PEI and poly{[N,N'-bis(2-octyldodecyl)naphthalene-1,4,5,8-bis(dicarboximide)-2,6-diyl]-alt-5,5'-(2,2'-bithiophene)} [P(NDI2OD-T2)] on indium tin oxide. We observed the vertical phase separation in such films, where PEI accumulates at the bottom and the top, sandwiching the semiconductor layer. The PEI interlayer on ITO reduces the electron injection barrier to the minimum value determined by Fermi level pinning, which, in turn, reduces the contact resistance by 5 orders of magnitude. Although we find no evidence for doping-induced polarons in P(NDI2OD-T2) upon mixing with PEI from optical absorption, more sensitive electron paramagnetic resonance measurements provide evidence for doping and an increased carrier density, at a very low level. This, in conjunction with an increased charge carrier mobility due to trap filling, results in an increase in the mixed polymer conductivity by 4 orders of magnitude relative to pure P(NDI2OD-T2). Consequently, both interfacial and bulk effects occur with notable magnitude in thin films formed from blended semiconductor polymer/PEI solution. Thus, this facile one-step procedure to form PEI interlayers must be applied with attention, as modification of the bulk semiconductor polymer (here doping) may occur simultaneously and might go un-noticed if not examined carefully.

Current theoretical approaches to inflectional morphology make extensive use of the two concepts of abstract feature decomposition and underspecification. Psycholinguistic models of inflection, in contrast, generally lack such more differentiated morphological analyses. This paper reports a series of behavioral experiments that investigate the processing of grammatical gender of nouns in German. The results of these experiments support the idea that elements in the mental lexicon may be underspecified with regard to their grammatical features. However, contrary to all established morphological and psycholinguistic approaches, we provide evidence that even the lexical representation of bare noun stems is characterized by underspecified gender information. The observation that the domain of underspecification of grammatical features extends from inflectional markers to noun stems, supports the idea that underspecification is a more general characteristic of the mental lexicon. We conclude that this finding is mainly driven by economical reasons: a feature (or feature value) that is never used for grammatical operations (e.g., inflectional marking or evaluation of agreement) is not needed in the language system at all.

We here demonstrate the use of solution processed NiOx thin films as the hole transport layer (HTL) in a thiophene–quinoxaline copolymer:fullerene solar cell. The NiOx films, which are prepared by UV-ozone treating a nickel formate precursor, outperform the solar cells prepared in this study that use PEDOT:PSS as HTL. The power conversion efficiency improves from 5.3% to 6.1% when replacing PEDOT:PSS with NiOx. Unlike most conventional ways of fabricating solution processed NiOx HTLs, our method does not require high temperature (>300 °C). In fact, we were able to produce high performing NiOx HTLs without the use of any thermal annealing. X-ray photoelectron spectroscopy revealed that a mixture of oxides and hydroxides is formed as a result of the UV-ozone treatment, which differs in composition from those formed by high temperature annealing; UV-ozone treatment produces NiOOH, while only the high temperature annealing produces any significant amount of NiO. Contact potential difference (CPD) measurements reveal an increased work function for all UV-ozone treated NiOx films, consistent with the presence of NiOOH at the surface. The high work function of the UV-ozone treated NiOx films leads to an improved energy level matching between the donor and the HTL, resulting in higher fill factor and hole injection current.

* indicates shared first authorship - The present study investigated the effects of selective attention on the processing of morphosyntactic errors in unattended parts of speech. Two groups of German native (L1) speakers participated in the present study. Participants listened to sentences in which irregular verbs were manipulated in three different conditions (correct, incorrect but attested ablaut pattern, incorrect and crosslinguistically unattested ablaut pattern). In order to track fast dynamic neural reactions to the stimuli, electroencephalography was used. After each sentence, participants in Experiment 1 performed a semantic judgement task, which deliberately distracted the participants from the syntactic manipulations and directed their attention to the semantic content of the sentence. In Experiment 2, participants carried out a syntactic judgement task, which put their attention on the critical stimuli. The use of two different attentional tasks allowed for investigating the impact of selective attention on speech processing and whether morphosyntactic processing steps are performed automatically. In Experiment 2, the incorrect attested condition elicited a larger N400 component compared to the correct condition, whereas in Experiment 1 no differences between conditions were found. These results suggest that the processing of morphosyntactic violations in irregular verbs is not entirely automatic but seems to be strongly affected by selective attention.

We investigate blended donor:acceptor (D:A) thin films of the two donors diindenoperylene (DIP) and poly(3-hexylthiophene) (P3HT) mixed with the strong acceptor 1,3,4,5,7,8-hexafluorotetracyanonaphthoquinodimethane (F6TCNNQ) using Polarization-Modulation Infrared Reflection-Absorption Spectroscopy (PMIRRAS). For DIP:F6TCNNQ thin films we first carry out a comprehensive study of the structure as a function of the D : A mixing ratio, which guides the analysis of the PMIRRAS spectra. In particular, from the red-shift of the nitrile (C[triple bond, length as m-dash]N) stretching of F6TCNNQ in the different mixtures with DIP, we quantify the average ground-state charge-transfer (GS-CT) to be ρavg = (0.84 ± 0.04) e. The PMIRRAS data for P3HT:F6TCNNQ blended films reveal nearly the same shift of the CT-affected C[triple bond, length as m-dash]N stretching peak for this system. This points towards a very similar CT strength for the two systems. We extend the analysis to the relative intensity of the C[triple bond, length as m-dash]N to the C[double bond, length as m-dash]C stretching modes of F6TCNNQ in the mixtures with DIP and P3HT, respectively, and support it with DFT calculations for the isolated F6TCNNQ. Such comparison allows to identify the vibrational signatures of the acceptor mono-anion in P3HT:F6TCNNQ, thus indicating a much stronger, integer CT-type interactions for this system, in agreement with available optical spectroscopy data. Our findings stress the importance of a simultaneous analysis of C[triple bond, length as m-dash]N and C[double bond, length as m-dash]C stretching vibrations in F6TCNNQ, or similar quinoid systems, for a reliable picture of the nature of GS-CT interactions.

Generally, the lack of long-range order in materials prevents from experimentally addressing their electronic band dispersion by angle-resolved photoelectron spectroscopy (ARPES), limiting such assessment to single crystalline samples. Here we demonstrate that the ARPES spectra of azimuthally disordered transition metal dichalcogenide (TMDC) monolayers with 2 H phase are dominated by their band dispersion along the two high symmetry directions Γ-K and Γ-M. We exemplify this by analyzing the ARPES spectra of four prototypical TMDCs within a mathematical framework, which allows to consistently explain the reported observations. A robust base for investigating TMDC monolayers significantly beyond single crystal samples is thus established. The complex nature of polycrystalline materials mean that characteristics such as their electronic band structure can be more challenging to interpret than their single crystal counterparts. Here, the authors present a framework based on angle-resolved photoemission spectroscopy to reveal the band dispersions for azimuthally disordered transition metal dichalcogenide polycrystalline monolayers.

A short lifetime is the main factor hindering the wider implementation of low-cost organic photovoltaics in large-area and outdoor applications. Ingress of oxygen and water vapour through non-ideal encapsulation layers is a known cause of degradation for polymer/fullerene based solar cells. To better understand the origin of this performance degradation, we study the effect of intentional exposure of the photo-active layer to simulated sunlight (AM1.5) in air both on the solar cell performance and on the molecular semiconductor materials. Cathode-free thin films of a blend of the electron donor polymer poly[2,3-bis-(3-octyloxyphenyl)quinoxaline-5,8-diyl-alt-thiophene-2,5-diyl] (TQ1) and the electron acceptor fullerene derivative [6,6]-phenyl-C70-butyric acid methyl ester (PC70BM) were exposed to simulated sunlight in air. Fourier-transform infrared spectra demonstrate the formation of carbonyl photo-oxidation products in the blend films, as well as in the pristine polymer and fullerene films. Solar cells prepared with photo-oxidized active layers show increasingly degraded electrical performance (lower short circuit current, open circuit voltage and fill factor) with increasing exposure time. The increased diode ideality factor indicates that trap-assisted recombination hinders device operation after exposure. The external quantum efficiency decreases drastically with increasing exposure time over the whole photon energy range, while the UV-vis absorption spectra of the blend films only show a mild photo-induced bleaching. This demonstrates that not only the photo-induced degradation of the solar cell performance is not predominantly caused by the loss in light absorption, but charge transport and collection are also hampered. This is explained by the fact that photo-oxidation of PC70BM causes bonds in its conjugated cage to break, as evidenced by the decreased π* intensity in C1s-NEXAFS spectra of PC70BM films. This degradation of unoccupied states of PC70BM will hinder the transport of photo-generated electrons to the electrode. Surface photovoltage spectroscopy gives direct evidence for gap states at the surface of a PC70BM film, formed after 2 hours of exposure and resulting in upward band bending at the PC70BM/air surface. These observations indicate that the photo-oxidation of PC70BM is likely to be the main cause of the performance degradation observed when the photoactive layer of a TQ1:PC70BM solar cell is intentionally exposed to light in air.

Optical and electrical properties of two-dimensional transition metal dichalcogenides (TMDCs) grown by chemical vapor deposition (CVD) are strongly determined by their microstructure. Consequently, the visualization of spatial structural variations is of paramount importance for future applications. Here we demonstrate how grain boundaries, crystal orientation, and strain fields can unambiguously be identified with combined lateral force microscopy (LFM) and transverse shear microscopy (TSM) for CVD-grown tungsten disulfide (WS2) monolayers, on length scales that are relevant for optoelectronic applications. Further, angle-dependent TSM measurements enable us to acquire the fourth-order elastic constants of monolayer WS2 experimentally. Our results facilitate high-throughput and nondestructive microstructure visualization of monolayer TMDCs, insights into their elastic properties, thus providing an accessible tool to support the development of advanced optoelectronic devices based on such two-dimensional semiconductors.

The control of the cathode work function (WF) is essential to enable efficient electron injection and extraction at organic semiconductor/cathode interfaces in organic electronic devices. In this paper, ultraviolet photoelectron spectroscopy is used to confirm that depositing an ultrathin layer of the moderately air-stable pentamethylrhodocene dimer onto various conducting electrodes, by either vacuum deposition or drop casting from solution, substantially reduces their WF to less than 3.6 eV, with 2.7 eV being the lowest attainable value. Detailed measurements of the Rh core levels with X-ray photoelectron spectroscopy reveal that the electron transfer from the molecule to the respective substrates is responsible for the appreciable WF reduction. Notably, even after air exposure, the WF of the donor-covered electrodes remains below those of typically used clean cathode metals, such as Al and Ag, rendering the approach appealing for practical applications. The WF reduction, together with the observed air stability of the covered electrodes, demonstrates the ability of the pentamethylrhodocene dimer to reduce the WF for a wide range of electrodes used in all-organic or organic-inorganic hybrid devices.

Planar and bulk heterojunctions of organic donor and acceptor molecules are used to understand elementary processes in photovoltaic cells. The electronic structure, interface and film morphology, excitonic behavior, device characteristics, and correlations between these properties are reviewed here using a wide range of material combinations.

Crystalline and uniform nanocolumns of the organic semiconductor diindenoperylene (DIP) were fabricated by glancing-angle deposition and employed in organic photovoltaic cells (OPVCs) forming an interdigitated donor/acceptor heterojunction, with fullerene as electron acceptor. In comparison to reference bilayer devices the nanocolumn-based solar cells exhibit increased power conversion efficiency. Based on a comprehensive structural and morphological analysis, we identify three advantages of the interdigitated nanocolumn structures: (i) The active donor/acceptor interface area, crucial for exciton dissociation, is increased and the column diameter is in the range of the exciton diffusion length. (ii) The molecular orientation of DIP is such in the nanocolumns that light absorption is enhanced. (iii) The ubiquitous presence of vertical interfaces throughout nanocolumn-based devices is further beneficial to light absorption, as it fully compensates wavelength-dependent interference effects within the device structure. This work shows how the benefits of nanocolumns can go beyond simple interface area enlargement to improve the efficiency of OPVCs.

In a comparative study, the stability of lithiated methylpyridine and the reactivity of side chain functionalized 4-methylypridines were investigated. In contrast to gas phase calculations, the observed N-coordination of the lithium to 4-methylpyridine anions is shown to be a solvent effect. Furthermore, lithiated methylpyridines are predicted to be dimeric in THF. The regioselectivity of the picoline anion alkylation was subject to an in-depth study. The activation barriers for the methylation of methylpyridine in Cα, C(3), and N position were determined and compared with partial NPA charges in an attempt to explain the observed selectivity. While there is no correlation of the charges with the selectivity, the calculated activation energies not only fit well with experimental conditions but also parallel the predominantly observed regioselectivity of alkylation at the exocyclic carbon atom. In agreement with the experiment no attack at the C(3) is observed. In case of a Cα and N methylation mixture (for the 4-(phenyl(tosyl)methylpyridine), the activation barrier difference between the two pathways diminishes to almost 0 kcal/mol.

We have studied the photo-degradation in air of a blend of [6,6]-phenyl-C61-butyric acid methyl ester (PCBM) and poly[2,3-bis-(3-octyloxyphenyl)quinoxaline-5,8-diyl-alt-thiophene-2,5-diyl] (TQ1), and how the photo-degradation affects the solar cell performance. Using near-edge X-ray absorption fine structure (NEXAFS) spectroscopy, changes to the electronic structure of TQ1 and PCBM caused by illumination in ambient air are investigated and compared between the pristine materials and the blend. The NEXAFS spectra show that the unoccupied molecular orbitals of TQ1 are not significantly changed by the exposure of pristine TQ1 to light in air, whereas those of PCBM are severely affected as a result of photo-induced degradation of PCBM. Furthermore, the photo-degradation of PCBM is accelerated by blending it with TQ1. While the NEXAFS spectrum of TQ1 remains unchanged upon illumination in air, its valence band spectrum shows that the occupied molecular orbitals are weakly affected. Yet, UV-Vis absorption spectra demonstrate photo-bleaching of TQ1, which is attenuated in the presence of PCBM in blend films. Illumination of the active layer of TQ1: PCBM solar cells prior to cathode deposition causes severe losses in electrical performance.

Over the past decades, electrospray ionization for mass spectrometry (ESI-MS) has become one of the most commonly employed techniques in analytical chemistry, mainly due to its broad applicability to polar and semipolar compounds and the superior selectivity which is achieved in combination with high resolution separation techniques. However, responsiveness of an analytical method also determines its suitability for the quantitation of chemical compounds; and in electrospray ionization for mass spectrometry, it can vary significantly among different analytes with identical solution concentrations. Therefore, we investigated the ESI-response behavior of 56 nitrogen-containing compounds including aromatic amines and pyridines, two compound classes of high importance to both, synthetic organic chemistry as well as to pharmaceutical sciences. These compounds are increasingly analyzed employing ESI mass spectrometry detection due to their polar, basic character. Signal intensities of the peaks from the protonated molecular ion (MH+) were acquired under different conditions and related to compound properties such as basicity, polarity, volatility and molecular size exploring their quantitative impact on ionization efficiency. As a result, we found that though solution basicity of a compound is the main factor initially determining the ESI response of the protonated molecular ion, other factors such as polarity and vaporability become more important under acidic solvent conditions and may nearly outweigh the importance of basicity under these conditions. Moreover, we show that different molecular descriptors may become important when using different types of instruments for such investigations, a fact not detailed so far in the available literature.

High mobility bipolar charge carrier transport in organic field-effect transistors (OFETs) can be enabled by a molecular passivation layer and selective electrode materials. Using tetratetracontane as passivation layer bipolar transport was realised in the organic semiconductors copper-phthalocyanine, diindenoperylene, pentacene, TIPS-pentacene and sexithiophene and mobilities of up to 0.1 cm2/V s were achieved for both electrons and holes. Furthermore, the trap and injection behaviour was analysed leading to a more general understanding of the transport levels of the used molecular semiconductors and their limitations for electron and hole transport in OFETs. With this knowledge the transistor operation can be further improved by applying two different electrode materials and a light-emitting transistor was demonstrated. Additionally, the effect of illumination on organic field-effect transistors was investigated for unipolar and bipolar devices. We find that the behaviour of photo-excited electrons and holes depends on the interface between the insulator and the semiconductor and the choice of contact materials. Whereas filling of electron traps by photo-generated charges and the related accumulation field are the reason for changes in charge carrier transport upon illumination without passivation layer, both types of charge carriers can be transported also in unipolar OFETs, if a passivation layer is present.

In organic photovoltaic (PV) cells, the well-established donor-acceptor (D/A) concept enabling photo-induced charge transfer between two partners with suitable energy level alignment has proven extremely successful. Nevertheless, the introduction of such a heterojunction is accompanied with additional energy losses as compared to an inorganic homojunction cell, owing to the presence of a charge-transfer (CT) state at the D/A interface. Based on the principle of detailed balance, a modified Shockley-Queisser theory is developed including the essential effects of interfacial CT states, that allows for a quantitative assessment of the thermodynamic efficiency limits of molecular D/A solar cells. Key parameters, apart from the optical gap of the absorber material, entering the model are the energy (ECT) and relative absorption strength (αCT) of the CT state. It is demonstrated how the open-circuit voltage (VOC) and thus the power conversion efficiency are affected by different parameter values. Furthermore, it is shown that temperature dependent device characteristics can serve to determine the CT energy, and thus the upper limit of VOC for a given D/A combination, as well as to quantify non-radiative recombination losses. The model is applied to diindenoperylene (DIP)-based photovoltaic devices, with open-circuit voltages between 0.9 and 1.4 V, depending on the partner, that have recently been reported.

Small-molecule photovoltaic cells using diindenoperylene (DIP) as a new donor material in combination with the fullerene C 60 as an electron acceptor are demonstrated. In addition to the successful application in planar and bulk heterojunction devices, a comprehensive analysis including structural studies, the determination of the energy level alignment and electrical transport investigations is given, stressing the correlation between growth conditions, fi lm morphology, and device performance. Due to pronounced crystallinity and a large surface area of DIP fi lms grown at elevated temperature, exceptionally high fi ll factors of almost 75% are achieved in planar heterojunction cells. Bulk heterojunctions exhibit large-scale phase separation forming a bicontinuous network of both molecular species, which enables effi cient exciton dissociation and charge carrier transport. The high ionization potential of DIP and the favorable energy level alignment with the fullerene C 60 yield large open circuit voltages close to 1 V and comparable power conversion effi ciencies of about 4% in both cell architectures.

Blends of organic electron and hole conductive materials are widely used for ambipolar charge-carrier transport and donor/acceptor (DA) photovoltaic cells. Thereby, the efficiency of these excitonic solar cells is correlated to the morphology of the interface between the donor and the acceptor materials, which in turns depends on the preparation conditions, the crystallization of the particular materials, and the interaction between the donor and acceptor molecules. In this contribution, the influence of the morphology on the solar cell architecture and performance will be discussed using different molecular DA combinations.

Ambipolar charge carrier transport in Copper phthalocyanine (CuPc) is studied experimentally in field-effect transistors and metal-insulator-semiconductor diodes at various temperatures. The electronic structure and the transport properties of CuPc attached to leads are calculated using density functional theory and scattering theory at the non-equilibrium Green's function level. We discuss, in particular, the electronic structure of CuPc molecules attached to gold chains in different geometries to mimic the different experimental setups. The combined experimental and theoretical analysis explains the dependence of the mobilityand the transmission coefficient on the charge carrier type (electrons or holes) and on the contact geometry. We demonstrate the correspondence between our experimental results on thick films and our theoretical studies of single molecule contacts. Preliminary results for fluorinated CuPc are discussed., 18 pages, 16 figures; to be published in Eur. Phys. J. Special Topics

Ambipolar organic semiconductor blends, i.e. mixtures of electron and hole conducting materials, attain growing interest due to their utilization in quasi-complementary organic field-effect transistors and organic photovoltaic cells. Many investigations in the latter field have reported an increase of the solar cell efficiency by optimizing the balance between charge carrier transport in phase-separated structures and exciton dissociation at the interface between these phases. Here we show the implications of blending molecular materials for structural, optical, and electrical properties in two model systems for organic photovoltaic cells. We have investigated blends and neat films of the hole transporting material Cu-phthalocyanine (CuPc) together with fullerene C 60 and Cu-hexadecafluoro-phthalocyanine (F 16 CuPc) as electron transporting materials, respectively. On the one hand, the difference in molecular structure of the spherical C 60 and the planar molecule CuPc leads to nanophase separation in a blend of both of them, causing charge carrier transport being limited by the successful formation of percolation paths. On the other hand, blends of the similar shaped CuPc and F 16 CuPc molecules entail mixed crystalline films, as can be clearly seen by X-ray scattering measurements. We discuss differences of both systems with respect to their microstructure as well as their electrical transport properties in diodes and field-effect transistors. Furthermore, we compare the photovoltaic properties of planar-and bulk-heterojunction devices under white light illumination to relate the different morphologies of both material systems to their performance in solar cells. Sketches of different molecular arrangements in blended systems. The formation of phase-separated (left) or molecularly mixed crystalline films (right) can occur, depending on the geometry of the involved molecules.

Blends of organic electron and hole conductive materials are widely used for ambipolar charge carrier transport and photovoltaic cells. An obvious choice for donor–acceptor blends are organic semiconducting materials in their hydrogenated and fluorinated form, since they combine potentially suitable electronic properties with structural compatibility of the two constituents. This study focuses on the structural, optical, and electrical properties of blends using hydrogenated copper-phthalocyanine ( H 16 CuPc ) in combination with its per-fluorinated version ( F 16 CuPc ) . Using X-ray scattering, scanning force microscopy and optical absorption measurements we show that mixed crystalline films are obtained by co-evaporation of the two materials. Electrical transport measurements reveal a profound reduction of the current for bipolar charge injection in mixed films. We discuss the formation of self-trapped charge transfer excitons as possible explanation for this unexpected behaviour, which impedes the usability of this system in photovoltaic cells.

Protein tyrosine phosphatase, non-receptor type 22 (PTPN22) inhibits T-cell activation and interleukin-2 (IL-2) production. The PTPN22(gain-of-function)+1858T(+) genotypes predispose to multiple autoimmune diseases, including early-onset (non-thymomatous) myasthenia gravis (MG). The disease association and the requirement of IL-2/IL-2 receptor signaling for intrathymic, negative T-cell selection have suggested that these genotypes may weaken T-cell receptor (TCR) signaling and impair the deletion of autoreactive T cells. Evidence for this hypothesis is missing. Thymoma-associated MG, which depends on intratumorous generation and export of mature autoreactive CD4(+) T cells, is a model of autoimmunity because of central tolerance failure. Here, we analyzed the PTPN22 +1858C/T single nucleotide polymorphism in 426 German Caucasian individuals, including 125 thymoma patients (79 with MG), and investigated intratumorous IL-2 expression levels. Unlike two previous studies on French and Swedish patients, we found strong association of PTPN22 +1858T(+) genotypes not only with early-onset MG (P=0.00034) but also with thymoma-associated MG (P=0.0028). IL-2 expression in thymomas with PTPN22 +1858T(+) genotypes (P=0.028) was lower, implying weaker TCR signaling. We conclude that the PTPN22(gain-of-function) variant biases towards MG in a subgroup of thymoma patients possibly by impeding central tolerance induction.