Real Function of Semiconducting Polymer in GaAs/Polymer Planar Heterojunction Solar Cells

We systematically investigated GaAs/polymer hybrid solar cells in a simple planar junction, aiming to fundamentally understand the function of semiconducting polymers in GaAs/polymer-based heterojunction solar cells. A library of semiconducting polymers with different band gaps and energy levels were evaluated in GaAs/polymer planar heterojunctions. The optimized thickness of the active polymer layer was discovered to be ultrathin (∼10 nm). Further, the open-circuit voltage (<i>V</i>_oc) of such GaAs/polymer planar heterojunctions was fixed around 0.6 V, regardless of the HOMO energy level of the polymer employed. On the basis of this evidence and others, we conclude that n-type GaAs/polymer planar heterojunctions are <i>not</i> type II heterojunctions as originally assumed. Instead, n-type GaAs forms a Schottky barrier with its corresponding anode, while the semiconducting polymer of appropriate energy levels can function as hole transport layer and/or electron blocking layer. Additionally, we discover that both GaAs surface passivation and thermal annealing can improve the performance of GaAs/polymer hybrid solar cells

Diarylation of Alkenes by a Cu-Catalyzed Migratory Insertion/Cross-Coupling Cascade

A strategy for the catalytic diarylation of alkenes is presented. The method involves the migratory insertion of alkenes into an Ar–Cu complex to generate a new C­(sp³)–Cu complex, which subsequently undergoes reaction with an aryl iodide to constitute a vicinal diarylation of an alkene. The method provides access to benzofuran- and indoline-containing products. Furthermore, highly diastereoselective examples are presented, allowing access to complex, stereochemically rich structures from simple alkene starting materials

Catalytic Enantioselective Diarylation of Alkenes

A method for the catalytic enantioselective diarylation of alkenes is presented. The method allowed for the synthesis of highly enantioenriched 2,3-dihydrobenzofurans and indolines containing molecules from readily available substrates. Furthermore, this method allowed for the enantioselective synthesis of quaternary carbons. Based on mechanism studies, the process likely functions by enantioselective insertion of an alkene into an Ar–CuBenzP* complex to generate a Csp³–Cu complex. Capture of this intermediate with an ArX led to formation of the desired product

Catalytic Enantioselective Diarylation of Alkenes

A method for the catalytic enantioselective diarylation of alkenes is presented. The method allowed for the synthesis of highly enantioenriched 2,3-dihydrobenzofurans and indolines containing molecules from readily available substrates. Furthermore, this method allowed for the enantioselective synthesis of quaternary carbons. Based on mechanism studies, the process likely functions by enantioselective insertion of an alkene into an Ar–CuBenzP* complex to generate a Csp³–Cu complex. Capture of this intermediate with an ArX led to formation of the desired product

Stereoselective Synthesis of All-Carbon Tetrasubstituted Alkenes from In Situ Generated Ketenes and Organometallic Reagents

Stereoselective synthesis of tetrasubstituted alkenes is a challenging problem in chemical synthesis. New protocols to access this important, yet simple, structural motif are of fundamental significance because they are found in many valuable molecules and can be utilized in a variety of important complexity building chemical transformations. The two-step strategy presented herein involves stereoselective generation of an alkenyl pseudohalide followed by a stereospecific metal-catalyzed cross-coupling

Heterogeneous Percolation in Poly(methylvinylsiloxane)/Silica Nanocomposites: The Role of Polymer–Particle Interaction

Agglomeration and linking of nanoparticles or aggregates lead to the formation of percolated particle networks and alter the mechanical enhancement in polymer nanocomposites. Although critical behaviors have been widely studied, the solidlike behavior is only well described under the condition of the uniform dispersion of nanoparticles. In this work, we illustrate the role of particle–polymer interaction in the uniformity of particle dispersion and mechanical enhancement. Two types of silica with different interfacial adhesion energies with poly(methylvinylsiloxane) were adopted, resulting in different uniformities of particle dispersion. The critical percolation concentrations from the yield shear stress and yield first normal stress difference are identical. A lower interfacial adhesion energy leads to a higher critical concentration. The preshear stress only affects the critical concentration but does not change the critical exponents, which rely on the particle–polymer interaction. The mechanical enhancement, expressed as the power-law dependence of the yield stresses on the filler content, exhibits extraordinarily large power-law exponents for nanocomposites with lower interfacial adhesion energy, seriously deviating from the theoretical prediction in homogeneous dispersion systems. Based on the structural information from small-angle X-ray scattering (SAXS)/ultrasmall-angle X-ray scattering (USAXS) and transmission electron microscopy (TEM), we propose a model describing the heterogeneous percolation of loose aggregates in the presence of compact aggregates. This model shows that the heterogeneity of aggregates, including the fraction of compact aggregates and their fractal dimension, is the key factor in the scaling relationship between the yield stress and the particle volume fraction

Synthesis of Alkaline Anion Exchange Membranes with Chemically Stable Imidazolium Cations: Unexpected Cross-Linked Macrocycles from Ring-Fused ROMP Monomers

In order to prepare base-stable, mechanically strong, and synthetically feasible alkaline anion exchange membranes (AAEMs) for applications in alkaline fuel cells, an imidazolium-fused cyclooctene monomer was prepared and subjected to ring-opening metathesis polymerization (ROMP) conditions. Surprisingly, macrocyclic oligomers were obtained instead of high molecular weight polymers. High-performance AAEMs were synthesized by using a bifunctional monomer to cross-link the macrocycles. The resultant AAEMs showed high ionic conductivities (σ_OH^– = 59 mS/cm at 50 °C), robust mechanical properties, and excellent alkaline stabilities

Visible Light Photoinitiated Metal-Free Living Cationic Polymerization of 4‑Methoxystyrene

Metal-free, visible light-initiated, living cationic polymerization of 4-methoxystyrene using 2,4,6-tri­(<i>p</i>-tolyl)­pyrylium tetrafluoroborate and methanol is demonstrated. Molecular weight and dispersity are controlled by the concentration of methanol. Initial mechanistic analysis suggests that methanol likely serves to regulate propagation of the cation chain end via reversible chain transfer in a manner analogous to reversible addition–fragmentation chain transfer polymerization

Revealing the Shear Effect on the Interfacial Layer in Polymer Nanocomposites through Nanofiber Reorientation

For polymer nanocomposites with attractive particle–polymer interactions, the interfacial layer consists of anchored and interpenetrating unanchored chains. The interfacial layer increases the effective hydrodynamic size of the nanoparticles and plays a critical role in mechanical reinforcement. Although it is clear that shear flow can lead to bonding-debonding of adsorbed chains, the effect of fast flow on the interfacial layer remains elusive. In this work, we adopted nanofiber-filled polymer nanocomposites with attractive fiber-polymer interactions to reveal the shear effect on the interfacial layer. We found a resting time-dependent stress overshoot in the reversal shear step of the preshear-resting-reversal shear protocol. Such a phenomenon disappeared either when nanofibers were surface-treated to reduce the attractive interaction or when the polymer matrix was replaced with one without attractive interactions. We ascribed the stress overshoot in the reversal shear to the collision and reorientation of nanofibers, and the decrease of overshoot strain with the resting time resulted from the decrease of nanofibers’ aspect ratio instead of Brownian motion and the relaxation of stretched interfacial chains. Because of the retarded relaxation in the interfacial layer, weak shear was sufficient to disentangle the nonadsorbed chains from the adsorbed ones, while a slow process was needed for the free chains re-interpenetrate, whose characteristic time matched the re-entanglement time of free polymer chains

A General Approach toward Electron Deficient Triazole Units to Construct Conjugated Polymers for Solar Cells

Triazole based structural units have been widely used to construct conjugated polymers for optoelectronic applications; yet the design and synthesis of such units have been limited to just a few known examples. We report a general yet versatile synthetic approach toward a diverse set of triazole based conjugated molecules bearing various electron accepting abilities. The structural differences of as-synthesized three new triazole acceptors have a significant impact on the optoelectronic properties of conjugated polymers incorporating these triazoles. Bulk heterojunction solar cells based on one of these new polymers, PyCNTAZ, feature a high open circuit voltage of ∼1 V and a notable efficiency of 8.4% with an active layer thickness around 300 nm