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Conjugated polymers need to be doped to increase charge carrier density and reach the electrical conductivity necessary for electronic and energy applications. While doping increases carrier density, Coulomb interactions between the dopant molecules and the localized carriers are poorly screened, causing broadening and a heavy tail in the electronic density‐of‐states (DOS). The authors examine the effects of dopant‐induced disorder on two complimentary charge transport properties of semiconducting polymers, the Seebeck coefficient and electrical conductivity, and demonstrate a way to mitigate them. Their simulations, based on a modified Gaussian disorder model with Miller‐Abrahams hopping rates, show that dopant‐induced broadening of the DOS negatively impacts the Seebeck coefficient versus electrical conductivity trade‐off curve. Increasing the dielectric permittivity of the polymer mitigates dopant‐carrier Coulomb interactions and improves charge transport, evidenced by simultaneous increases in conductivity and the Seebeck coefficient. They verified this increase experimentally in iodine‐doped P3HT and P3HT blended with barium titanate (BaTiO3) nanoparticles. The addition of 2% w/w BaTiO3 nanoparticles increased conductivity and Seebeck across a broad range of doping, resulting in a fourfold increase in power factor. Thus, these results show a promising path forward to reduce the dopant‐charge carrier Coulomb interactions and mitigate their adverse impact on charge transport., Organic electronic materials must be doped to increase their conductivity, but dopants increase energetic disorder and impede the motion of charge carriers. Here the authors show that the addition of nanoparticles having very high dielectric constants effectively screens the interaction between dopants and charge carriers, resulting in significant improvements in conductivity and the thermoelectric power factor.

This review focuses on the recent developments in our understanding of active layer morphologies for organic photovoltaic cells and approaches to obtain active layer morphologies for high power conversion efficiencies. The evolution of active layer morphologies, as studied by high resolution electron microscopy, X-ray and neutron scattering, and dynamic secondary ion mass spectrometry, is covered, along with strategies including the use of small molecule additives, polymer nanowires and polymer nanoparticles to realize active layer morphologies. © 2012 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys, 2012

Nanoporous polymer thin films produced from ordered block copolymer precursors have received considerable attention, because they can be used in many applications including templating, separation, catalysis, and sensors. Since 1988, various block copolymers have been used to prepare nanoporous thin films via the selective removal of degradable minor components from self-assembled block copolymers. For cylinder-forming block copolymers, selective etching of the cylindrical microdomain in an ordered block copolymer results in the formation of nanoscopic channels. Specially, if the etchable cylinders are orientated normal to the film surface, removal of the cylinders will lead to the nanolithographic masks used in block-copolymer lithography. Currently, the generation of nanoporous materials from ordered block copolymers relies on a selective etching protocol that does not compromise the integrity of the matrix material. Ozonolysis, UV degradation, reactive ion etching (RIE), and chemical etching are the methods that are commonly used for the removal of minor components to create nanopores. However, the number of polymers that can be degraded under mild reaction conditions in the thin-film state is limited. The preparation of nanoporous thin films from block copolymers without a degradable component requires a rational design of the polymer. In principle, to generate nanopores from self-assembled block copolymers, it is not necessary to degrade the backbone bonds in the minor component; rather, a cleavage of the juncture between two immiscible blocks is sufficient. Therefore, if one could put a cleavable juncture into a block copolymer; the cleavage will not depend on the chemical nature of the minor component and should be applicable to a much larger variety of block copolymers. Cleavage of the juncture point of block copolymer in the ordered state followed by removal of the minor component via selective solvents is therefore a very promising strategy for the generation of nanoporous structures. For most of the nanoporous polymer thin films prepared to date, one of the major problems is the lack of long-range order in the nanopore array, which prevents them from being used in applications where addressability is required (e.g., magnetic storage devices). Long-range order in thin films of the precursor block copolymers is a prerequisite for obtaining nanoporous materials with well-ordered pores. We have recently demonstrated that the solvent-annealing of thin films of polystyrene-block-poly(ethylene oxide) (PS-b-PEO) diblock copolymers leads to highly ordered arrays of PEO cylinders oriented normal to the film surface. The long-range lateral order and the orientation in the annealed PS-b-PEO thin films arise from the strong nonfavorable interactions between PS and PEO, enhanced mobility caused by the presence of solvent, as well as the directionality of solvent evaporation. The subsequent removal of the PEO domain will lead to nanoporous films with identical long-range order. However, the poor degradability of PEO prevents the direct generation of nanopores from ordinary PS-b-PEO. Mao and Hillmyer recently reported the successful use of hydroiodic acid to degrade PEO in the bulk sample of PS-b-PEO, but the harsh reaction conditions they used are not applicable to thin films. To impart the degradability to the PS-b-PEO system, we recently synthesized a triblock copolymer, polystyrene-bpoly(methyl methacrylate)-b-poly(ethylene oxide) (PS-bPMMA-b-PEO), where PS is the major component and PMMA and PEO are minor components. By taking the advantage of the photodegradability of the PMMA mid-block, nanoporous thin films with excellent long-range order suitable for block copolymer lithography were prepared. In this method, the degradation efficiency depends critically on the molecular weight and phase behavior of the PMMA block, and only when PMMA formed a distinct microdomain did efficient degradation occur. In this paper, we show that by placing a cleavable juncture, a triphenylmethyl (trityl) ether linkage, between PS and PEO, C O M M U N IC A IO N

Polymer-based mixed ionic–electronic conductors (MIECs) are desired for both bulk and interfacial materials in next-generation energy storage and electronic devices. Polymer-based MIECs contain two principal components, one for electronic conduction and the other for ionic conduction. The central problem is the lack of a general approach to control the molecular packing and morphology of the constituent components that will afford the ability to easily tune transport properties. This study demonstrates the efficacy of a modular method based on polymer nanoparticle self-assembly to achieve MIECs with tunable conductivity. This work uses poly(3-hexylthiophene) nanoparticles as the electronic conductor and lithium ion-doped poly(vinylpyridine) nanoparticles as the ionic conductors. AC impedance spectroscopic studies show that nanoparticle–nanoparticle interfaces in unary assemblies do not impede ion transport in the solid state. AC impedance spectroscopy and DC steady-state conductivity measurements show that binary nanoparticle assemblies exhibit concurrent ionic and electronic conduction. The power-law scaling percolation of both the ionic and electronic transport displays nonuniversal values of transport critical exponent, revealing different transport mechanisms. The simplicity of fabrication combined with the versatility in obtainable transport properties illustrates the power of using nanoparticle assemblies as a means to realize MIEC polymer mesoscale morphologies.

Hybrid organic/inorganic perovskite solar cells are invigorating the photovoltaic community due to their remarkable properties and efficiency. However, many perovskite solar cells show an undesirable current–voltage (I–V) hysteresis in their forward and reverse voltage scans, working to the detriment of device characterization and performance. This hysteresis likely arises from slow ion migration in the bulk perovskite active layer to interfaces which may induce charge trapping. It is shown that interfacial chemistry between the perovskite and charge transport layer plays a critical role in ion transport and I–V hysteresis in perovskite-based devices. Specifically, phenylene vinylene polymers containing cationic, zwitterionic, or anionic pendent groups are utilized to fabricate charge transport layers with specific interfacial ionic functionalities. The interfacial-adsorbing boundary induced by the zwitterionic polymer in contact with the perovskite increases the local ion concentration, which is responsible for the observed I–V hysteresis. Moreover, the ion adsorbing properties of this interface are exploited for perovskite-based memristors. This fundamental study of I–V hysteresis in perovskite-based devices introduces a new mechanism for inducing memristor behavior by interfacial ion adsorption.

This research aims to develop schemes for the programmed assembly of molecular materials. The underlying premise guiding this work is that structural information stored in the molecular constituents dictates their condensed phase organization (i.e. through the sum of all non-covalent interactions). The challenge then is to design molecular building blocks that encode this information in a decipherable manner. Our approach has relied on the use of organic nanoarchitectures, which we believe will serve as “modular units” for programmed assembly. Large molecules of well defined constitution and geometry offer the advantage that a high level of information can be incorporated into a single unit. The design and synthesis of nanoscale macrocyclics and macrobicyclics for this purpose has been achieved. Studies on the solution aggregation of the macrocyclics have provided a unique opportunity to glimpse some of the interactions which may influence solid state ordering. These building blocks are being used for the rational design of novel materials such as porous organic crystals and tubular mesophases.

Chirality in molecular systems plays profoundly important roles in chemistry and physics. Most chemistry students are introduced to the concept of chirality through demonstrations of the interaction of chiral molecules with polarized light manifested as an "optical rotation" leading to the "(+)" and "(-)" [or dextrorotatory (d-) and levorotatory (l-)] designations of chiral compounds, with the subsequent determination of absolute stereochemical configuration by chemical or physical means enabling application of the familiar "R" and "S" labels. Although the intrinsic molecular parameters that control the dissymmetric light-matter interaction in chiral systems are well understood, we have only recently begun to ask questions regarding the role of local molecular environment and hidden heterogeneities associated with the ensemble-averaged molecular chiroptical response. In this mini-review, we discuss some of our recent research on application of single-molecule spectroscopy as a tool for probing heterogeneities and fluctuations of chiroptical dissymmetries in condensed phase.

We have found that bromo(triphenylphosphine)copper(I), an air-stable and soluble copper(I) complex, can be used as a catalyst in the synthesis of diaryl ethers. Using this catalyst, we have synthesized diaryl ethers from electron-rich aryl bromides and electron-rich phenols in the presence of cesium carbonate, in 17–24 h, in NMP. We also found that electron-deficient aryl bromides couple with phenols in the presence of cesium carbonate, in 6 h in NMP at 70°C, without the catalyst.

We report mild synthetic protocols for the formation of aryl−carbon, aryl−nitrogen, and aryl−oxygen bonds based on soluble, well-defined copper(I) catalysts. These protocols do not require the use of palladium and/or expensive ligands.

We report a mild, palladium-free synthetic protocol for the cross-coupling reaction of aryl iodides and thiols using 10 mol % CuI and 10 mol % neocuproine, with NaOt-Bu as the base, in toluene at 110 °C. Using this protocol, we have shown that a variety of aryl sulfides can be synthesized in excellent yields from readily available iodides and thiols.

Interface engineering is critical for achieving efficient solar cells, yet a comprehensive understanding of the interface between a metal electrode and electron transport layer (ETL) is lacking. Here, a significant power conversion efficiency (PCE) improvement of fullerene/perovskite planar heterojunction solar cells from 7.5% to 15.5% is shown by inserting a fulleropyrrolidine interlayer between the silver electrode and ETL. The interface between the metal electrode and ETL is carefully examined using a variety of electrical and surface potential techniques. Electrochemical impedance spectroscopy (EIS) measurements demonstrate that the interlayer enhances recombination resistance, increases electron extraction rate, and prolongs free carrier lifetime. Kelvin probe force microscopy (KPFM) is used to map the surface potential of the metal electrode and it indicates a uniform and continuous work function decrease in the presence of the fulleropyrrolidine interlayer. Additionally, the planar heterojunction fullerene/perovskite solar cells are shown to have good stability under ambient conditions.

[reaction: see text] We report a copper(I)-catalyzed procedure for the synthesis of 1,3-enynes. This method affords a variety of enynes in good to excellent yields. This method can tolerate a variety of functional groups, does not require the use of expensive additives, and is palladium-free.

A chiral Zn(II)–salen complex tethered with poly(ethylene glycol) (PEG) was synthesized. This soluble polymer-supported complex was found to catalyze the asymmetric addition of diethylzinc to a series of aromatic aldehydes in good yields and with good enantiomeric ratio (er). The PEG-supported catalyst could be recycled and reused up to three times. The reactivity and selectivity of the catalyst was dependent on the nature of the linker between the polymer and the complex.

We review polymer-based electronics and photovoltaics to provide the reader with a sense of how the field has developed, where we stand at present, and what possibilities are looming in the future. Expertise in areas ranging from synthesis to morphology to device design was sought to achieve this end. While these reviews cannot be exhaustive, they do provide a snapshot of the field at present and give some sense of where the key impediments are.