Quantification of Grafting Densities Achieved via Modular “Grafting‐to” Approaches onto Divinylbenzene Microspheres

The surface modification of divinylbenzene (DVB)‐based microspheres is performed via a combination of reversible addition fragmentation chain transfer (RAFT) polymerization and rapid hetero‐Diels–Alder (HDA) chemistry with the aim of quantifying the grafting densities achieved using this “grafting‐to” method. Two variants of the RAFT‐HDA concept are employed to achieve the functionalization of the microspheres. In the first approach, the microspheres are functionalized with a highly reactive diene, i.e., cyclopentadiene, and are subsequently reacted with polystyrene chains (number‐averaged molecular weight, M_n = 4200 g mol^?1; polydispersity index, PDI = 1.12.) that carry a thiocarbonyl moiety functioning as a dienophile. The functionalization of the microspheres is achieved rapidly under ambient conditions, without the aid of an external catalyst. The surface grafting densities obtained are close to 1.2 × 10²⁰ chains per gram of microspheres. In the second approach, the functionalization proceeds via the double bonds inherently available on the microspheres, which are reacted with poly(isobornyl acrylate) chains carrying a highly dienophilic thiocarbonyl functionality; two molecular weights (M_n = 6000 g mol^?1, PDI = 1.25; M_n = 26 000 g mol^?1, PDI = 1.26) are used. Due to the less reactive nature of the dienes in the second approach, functionalization is carried out at elevated temperatures (T = 60 °C) yet in the absence of a catalyst. In this case the surface grafting density is close to 7 chains nm^?2 for M_n = 6000 g mol^?1 and 4 chains nm^?2 for M_n = 26 000 g mol^?1, or 2.82 × 10¹⁹ and 1.38 × 10¹⁹ chains g^?1, respectively. The characterization of the microspheres at various functionalization stages is performed via elemental analysis for the quantification of the grafting densities and attenuated total reflectance (ATR) IR spectroscopy as well as confocal microscopy for the analysis of the surface chemistry.     

Influence of Molecular Weight on the Performance of Organic Solar Cells Based on a Fluorene Derivative

The performance of organic photovoltaic (OPV) bulk‐heterojunction blends comprising a liquid‐crystalline fluorene derivative and a small‐molecular fullerene is found to increase asymptotically with the degree of polymerization of the former. Similar to various thermodynamic transition temperatures as well as the light absorbance of the fluorene moiety, the photocurrent extracted from OPV devices is found to strongly vary with increasing oligomer size up to a number average molecular weight, M_n ≈ 10 kg mol^?1, but is rendered less chain‐length dependent for higher M_n as the fluorene derivative gradually adopts polymeric behavior.     

Photo‐Induced Functionalization of Spherical and Planar Surfaces via Caged Thioaldehyde End‐Functional Polymers

The synthesis and application of a novel reversible addition‐fragmentation chain transfer (RAFT) agent carrying a photocaged thioaldehyde moiety is described (λ_max = 355 nm). RAFT polymerization of styrene, dimethylacrylamide and a glycomonomer is evidenced (3600 g mol^?1 ≤ M_n ≤ 15 000 g mol^?1; 1.07 ≤ ? ≤ 1.20) with excellent end‐group fidelity. The photogenerated thioaldehyde on the chain ends can undergo hetero Diels–Alder reactions with dienes as well as reactions with nucleophiles. The terminal photoreactive polymers are photografted to porous diene‐reactive polymeric microspheres. The grafted particles are in‐depth characterized via scanning electron microscopy, elemental analysis, X‐ray photoelectron spectroscopy, and high resolution FT‐IR microscopy, leading to a qualitative as well as quantitative image of the core–shell objects. Grafting densities up to 0.10 molecules nm^?2 are reached. The versatility of the thioaldehyde ligation is evidenced by spatially resolved grafting of polystyrene onto nucleophilic groups present in poly (dopamine) (PDA)‐coated glass slides and silicon wafers via two‐photon direct laser writing (DLW) imaged by ToF‐SIMS. The combination of thioaldehyde ligation, RAFT polymerization, and DLW allows for the spatially resolved grafting of a vast range of polymers onto various substrates in any desired pattern with sub‐micrometer resolution.     

Magnetic and Temperature‐Sensitive Release Gels from Supramolecular Polymers

Supramolecular gels consisting of trivalent polyisobutylene and bivalent poly(ethylene oxide) are generated. Strong hydrogen bonding interactions, affixed to the end‐group moieties of the respective polymers (binding constant K_assn = 10⁵ M ^–1), serve as molecular glue, leading to the formation of weak gels. Two different gels were prepared: one, with a short telechelic poly(ethylene glycol) (PEG) segment (gel A), and one with a longer PEG segment (number‐average molecular weight M_n = 2000 g mol^–1) (gel B). Both gels show a significant increase in viscosity upon mixing of the two polymeric components, with a lag time of several minutes, indicative of nucleation mechanisms as the formation principle. However, only gel A displays classical gel‐like behavior, with a loss modulus G′ larger than the storage modulus G″ after formation. Both gels display microphase‐separated behavior with a spacing between 4–5 nm as probed via small‐angle X‐ray scattering (SAXS) and transmission electron microscopy (TEM) measurements. The incorporation of magnetic nanoparticles (Fe₂O₃; radius r = 3.5 nm) is successfully achieved, generating new magnetic gels with strongly thermoresponsive properties, displaying a strong temperature‐dependent release profile of included dye molecules. Magnetic measurements indicate a superparamagnetic behavior of the incorporated nanoparticles, prospecting the application as magneto‐sensitive delivery gels for pharmaceutical purposes.     

Tuning the Molecular Weight of the Electron Accepting Polymer in All‐Polymer Solar Cells: Impact on Morphology and Charge Generation

Molecular weight is an important factor determining the morphology and performance of all‐polymer solar cells. Through the application of direct arylation polycondention, a series of batches of a fluorinated naphthalene diimide‐based acceptor polymer are prepared with molecular weight varying from M_n = 20 to 167 kDa. Used in conjunction with a common low bandgap donor polymer, the effect of acceptor molecular weight on solar cell performance, morphology, charge generation, and transport is explored. Increasing the molecular weight of the acceptor from M_n = 20 to 87 kDa is found to increase cell efficiency from 2.3% to 5.4% due to improved charge separation and transport. Further increasing the molecular weight to M_n = 167 kDa however is found to produce a drop in performance to 3% due to liquid–liquid phase separation which produces coarse domains, poor charge generation, and collection. In addition to device studies, a systematic investigation of the microstructure and photophysics of this system is presented using a combination of transmission electron microscopy, grazing‐incidence wide‐angle X‐ray scattering, near‐edge X‐ray absorption fine‐structure spectroscopy, photoluminescence quenching, and transient absorption spectroscopy to provide a comprehensive understanding of the interplay between morphology, photophysics, and photovoltaic performance.     

A Direct Approach to Organic/Inorganic Semiconductor Hybrid Particles via Functionalized Polyfluorene Ligands

Controlled Suzuki–Miyaura coupling polymerization of 7′‐bromo‐9′,9′‐dioctyl‐fluoren‐2′‐yl‐4,4,5,5‐tetramethyl‐[1,3,2]dioxaborolane initiated by bromo(4‐tert‐butoxycarbonylamino‐phenyl)(tri‐tert‐butylphosphine)palladium ( 1 ) or bromo(4‐diethoxyphosphoryl‐phenyl)(tri‐tert‐butylphosphine)palladium ( 2 ) yields functionalized polyfluorenes (M_n = 4 × 10³ g mol^?1, M_w/M_n < 1.2) with a single amine or phosphonic acid, respectively, end‐group. High temperature synthesis of cadmium selenide quantum dots with these functionalized polyfluorenes as stabilizing ligands yields hybrid particles consisting of good quality (e.g. emission full width at half maximum of 30 nm; size distribution σ < 10%) inorganic nanocrystals with polyfluorene attached to the surface, as corroborated by transmission electron microscopy analysis and analytical ultracentrifugation. Sedimentation studies on particle dispersions show that a substantial portion (ca. half) of the phosphonic acid terminated polyfluorene ligands is bound to the inorganic nanocrystals, versus ca. 5% for the amino‐functionalized polyfluorene ligands. Single particle micro‐photoluminescence spectroscopy shows an efficient and complete energy transfer from the polyfluorene layer to the inorganic quantum dot.     

Monitoring the Formation of a CH3NH3PbI3–xClx Perovskite during Thermal Annealing Using X‐Ray Scattering

Grazing incidence wide and small angle X‐ray scattering (GIWAXS and GISAXS) measurements have been used to study the crystallization kinetics of the organolead halide perovskite CH₃NH₃PbI_3–xCl_x during thermal annealing. In situ GIWAXS measurements recorded during annealing are used to characterize and quantify the transition from a crystalline precursor to the perovskite structure. In situ GISAXS measurements indicate an evolution of crystallite sizes during annealing, with the number of crystallites having sizes between 30 and 400 nm increasing through the annealing process. Using ex situ scanning electron microscopy, this evolution in length scales is confirmed and a concurrent increase in film surface coverage is observed, a parameter crucial for efficient solar cell performance. A series of photovoltaic devices are then fabricated in which perovskite films have been annealed for different times, and variations in device performance are explained on the basis of X‐ray scattering measurements.     

Photophysics of Molecular‐Weight‐Induced Losses in Indacenodithienothiophene‐Based Solar Cells

The photovoltaic performance and optoelectronic properties of a donor–acceptor copolymer are reported based on indacenodithienothiophene (IDTT) and 2,3‐bis(3‐(octyloxy)phenyl)quinoxaline moieties (PIDTTQ) as a function of the number‐average molecular weight (M_n). Current–voltage measurements and photoinduced charge carrier extraction by linear increasing voltage (photo‐CELIV) reveal improved charge generation and charge transport properties in these high band gap systems with increasing M_n, while polymers with low molecular weight suffer from diminished charge carrier extraction because of low mobility–lifetime (μτ) product. By combining Fourier‐transform photocurrent spectroscopy (FTPS) with electroluminscence spectroscopy, it is demonstrate that increasing M_n reduces the nonradiative recombination losses. Solar cells based on PIDTTQ with M_n = 58 kD feature a power conversion efficiency of 6.0% and a charge carrier mobility of 2.1 × 10^?4 cm² V^?1 s^?1 when doctor bladed in air, without the need for thermal treatment. This study exhibits the strong correlations between polymer fractionation and its optoelectronics characteristics, which informs the polymer design rules toward highly efficient organic solar cells.     

Simultaneous Modification of Bottom‐Contact Electrode and Dielectric Surfaces for Organic Thin‐Film Transistors Through Single‐Component Spin‐Cast Monolayers

An efficient process is developed by spin‐coating a single‐component, self‐assembled monolayer (SAM) to simultaneously modify the bottom‐contact electrode and dielectric surfaces of organic thin‐film transistors (OTFTs). This effi cient interface modifi cation is achieved using n‐alkyl phosphonic acid based SAMs to prime silver bottom‐contacts and hafnium oxide (HfO₂) dielectrics in low‐voltage OTFTs. Surface characterization using near edge X‐ray absorption fi ne structure (NEXAFS) spectroscopy, X‐ray photoelectron spectroscopy (XPS), attenuated total reflectance Fourier transform infrared (ATR‐FTIR) spectroscopy, atomic force microscopy (AFM), and spectroscopic ellipsometry suggest this process yields structurally well‐defi ned phosphonate SAMs on both metal and oxide surfaces. Rational selection of the alkyl length of the SAM leads to greatly enhanced performance for both n‐channel (C₆₀) and p‐channel (pentacene) based OTFTs. Specifi cally, SAMs of n‐octylphos‐phonic acid (OPA) provide both low‐contact resistance at the bottom‐contact electrodes and excellent interfacial properties for compact semiconductor grain growth with high carrier mobilities. OTFTs based on OPA modifi ed silver electrode/HfO₂ dielectric bottom‐contact structures can be operated using < 3V with low contact resistance (down to 700 Ohm‐cm), low subthreshold swing (as low as 75 mV dec^?1), high on/off current ratios of 107, and charge carrier mobilities as high as 4.6 and 0.8 cm² V^?1 s^?1, for C60 and pentacene, respectively. These results demonstrate that this is a simple and efficient process for improving the performance of bottom‐contact OTFTs.     

3D Hexagonal (R‐3m) Mesostructured Nanocrystalline Titania Thin Films: Synthesis and Characterization

A straightforward and reproducible synthesis of crack‐free large‐area thin films of 3D hexagonal (R‐3m) mesostructured nanocrystalline titania (meso‐nc‐TiO₂) using a Pluronic triblock copolymer (P123)/1‐butanol templating system is described. The characterization of the films is achieved using a combination of electron microscopy (high‐resolution scanning electron microscopy and scanning transmission electron microscopy), grazing‐incidence small‐angle X‐ray scattering, in situ high‐temperature X‐ray diffraction, and variable‐angle spectroscopic ellipsometry. The mesostructure of the obtained films is found to be based upon a 3D periodic array of large elliptically shaped cages with diameters around 20 nm interconnected by windows of about 5 nm in size. The mesopores of the film calcined at 300 °C are very highly ordered, and the titania framework of the film has a crystallinity of 40 % being composed of 5.8 nm sized anatase crystallites. The film displays high thermal stability in that the collapse of the pore architecture is incomplete even at 600 °C. The accessible surface area of 3D hexagonal meso‐nc‐TiO₂ estimated by the absorption of methylene blue is nearly twice as large as that of 2D hexagonal meso‐nc‐TiO₂ at the same annealing temperature.     

Organic Thin‐Film Transistors: Simultaneous Modification of Bottom‐Contact Electrode and Dielectric Surfaces for Organic Thin‐Film Transistors Through Single‐Component Spin‐Cast Monolayers (Adv. Funct. Mater. 8/2011)

An efficient process is developed by spin‐coating a single‐component, self‐assembled monolayer (SAM) to simultaneously modify the bottom‐contact electrode and dielectric surfaces of organic thin‐film transistors (OTFTs). This effi cient interface modifi cation is achieved using n‐alkyl phosphonic acid based SAMs to prime silver bottom‐contacts and hafnium oxide (HfO₂) dielectrics in low‐voltage OTFTs. Surface characterization using near edge X‐ray absorption fi ne structure (NEXAFS) spectroscopy, X‐ray photoelectron spectroscopy (XPS), attenuated total reflectance Fourier transform infrared (ATR‐FTIR) spectroscopy, atomic force microscopy (AFM), and spectroscopic ellipsometry suggest this process yields structurally well‐defi ned phosphonate SAMs on both metal and oxide surfaces. Rational selection of the alkyl length of the SAM leads to greatly enhanced performance for both n‐channel (C₆₀) and p‐channel (pentacene) based OTFTs. Specifi cally, SAMs of n‐octylphos‐phonic acid (OPA) provide both low‐contact resistance at the bottom‐contact electrodes and excellent interfacial properties for compact semiconductor grain growth with high carrier mobilities. OTFTs based on OPA modifi ed silver electrode/HfO₂ dielectric bottom‐contact structures can be operated using < 3V with low contact resistance (down to 700 Ohm‐cm), low subthreshold swing (as low as 75 mV dec^?1), high on/off current ratios of 107, and charge carrier mobilities as high as 4.6 and 0.8 cm² V^?1 s^?1, for C60 and pentacene, respectively. These results demonstrate that this is a simple and efficient process for improving the performance of bottom‐contact OTFTs.     

Modular Ligation of Thioamide Functional Peptides onto Solid Cellulose Substrates

Hetero Diels‐Alder (HDA) cycloaddition – as an effective modular conjugation approach – is employed to graft thioamide endfunctional oligopeptides onto solid cyclopentadienyl (Cp) functional cellulose substrates generating cellulose‐peptide hybrid materials. The highly reactive Cp moieties serve as diene functionality in the consecutive HDA reaction on the biosubstrate surface. Oligopeptides (i.e., the model peptide Gly‐Gly‐Arg‐Phe‐Pro‐Trp‐Trp‐Gly and the antimicrobial peptide tritrpticin) are functionalized at their N‐termini employing strongly electron deficient thiocarbonyl thio compounds resulting in biomacromolecules bearing a thioamide endgroup. The dienophile‐ functional peptides readily undergo HDA reactions at ambient temperature and under mild conditions in solution with synthetic polymers as well as on solid (bio)substrates. An in‐depth investigation is provided of the influence of the temperature, the Lewis acid catalysis and the side group exchange of thioamide functional oligopeptides reacting with Cp terminated poly(methyl methacrylate) (M_n = 2100 g·mol^?1, PDI = 1.1) in homogenous solution as well as Cp functionalized cellulose in a heterogeneous system. To assess the success of the grafting reaction, the soluble samples were subjected to characterization methods such as size exclusion chromatography (SEC) and SEC‐electrospray ionization mass spectrometry (SEC‐ESI‐MS). The heterogeneous “grafting‐to” reactions were monitored using high resolution attenuated total reflection (ATR) Fourier transform infrared microscopy (HR‐FTIRM) imaging, X‐ray photoelectron spectroscopy (XPS) and elemental analysis. Evaluation via elemental analysis leads to quantitative peptide cellulose surface loading capacities.     

Effect of Molecular Weight on the Structure and Morphology of Oriented Thin Films of Regioregular Poly(3‐hexylthiophene) Grown by Directional Epitaxial Solidification

Regioregular head‐to‐tail (HT)‐coupled poly(3‐hexylthiophene‐2,5‐diyl) (P3HT) with a weight‐average molecular weight (M_w) in the 7.3–69.6 kDa range is crystallized by directional epitaxial solidification in 1,3,5‐trichlorobenzene (TCB) to yield highly oriented thin films. An oriented and periodic lamellar structure consisting of crystalline lamellae separated by amorphous interlamellar zones is evidenced by atomic force microscopy (AFM) and transmission electron microscopy (TEM). Both the overall crystallinity as well as the orientation of the crystalline lamellae decrease significantly with increasing M_w. The total lamellar periodicity is close to the length of “fully extended” chains for M_w = 7.3 kDa (polystyrene‐equivalent molecular weight, eq. PS) and it saturates to a value of ca. (25–28) ± 2 nm for M_w ≥ 18.8 kDa (eq. PS). This behavior is attributed to a transition from an oligomeric‐like system, for which P3HT chains are essentially in a fully extended all‐trans conformation and do not fold, to a semicrystalline system that involves a periodic alternation of crystalline lamellae separated by extended amorphous interlamellar zones, which harbor chain folds, chain ends, and tie molecules. For P3HT with M_w of ca. 7.3 kDa (eq. PS), epitaxial crystallization on TCB allows for the growth of both “edge‐on” and “flat‐on” oriented crystalline lamellae on the TCB substrate. The orientation of the lamellae is attributed to 1D epitaxy. Because of the large size of the “flat‐on” crystalline lamellae, a characteristic single‐crystal electron diffraction pattern corresponding to the [001] zone was obtained by selected area electron diffraction (SAED), indicating that P3HT crystallizes in a monoclinic unit cell with a = 16.0 Å, b = 7.8 Å, c = 7.8 Å, and γ = 93.5°.     

Structure and Morphology of PDI8‐CN2 for n‐Type Thin‐Film Transistors

A multiscale investigation of N,N′‐bis(n‐octyl)‐x:y, dicyanoperylene‐3,4:9,10‐bis(dicarboximide), PDI8‐CN2, shows the same molecular arrangement in the bulk and in thin films sublimated on SiO₂/Si wafers. Non‐conventional powder diffraction methods and theoretical calculations concur to provide a coherent picture of the crystalline structure. X‐ray diffraction (XRD) and atomic force microscopy (AFM) analyses of films of different thickness deposited at different substrate temperatures indicate the existence of two temperature‐dependent deposition regimes: a low‐temperature (room temperature) regime and a high‐temperature (80–120 °C) one, each characterized by different growth mechanisms. These mechanisms eventually result in different morphological and structural features of the films, which appear to be highly correlated with the trend of the electrical parameters that are measured in PDI8‐CN2‐based field‐effect transistors.     

Naphthyl and Thionaphthyl End‐Capped Oligothiophenes as Organic Semiconductors: Effect of Chain Length and End‐Capping Groups

Two series of oligothiophenes (OThs), NaTn and TNTn (n = 2–6 represents the number of thiophene rings), end‐capped with naphthyl and thionaphthyl units have been synthesized by means of Stille coupling. Their thermal properties, optical properties, single crystal structures, and organic field‐effect transistor performance have been characterized. All oligomers display great thermal stability and crystallinity. The crystallographic structures of NaT2 , NaT3 , TNT2 , and TNT3 have been determined. The crystals of NaT2 and NaT3 are monoclinic with space group P2₁/C, while those of TNT2 and TNT3 are triclinic and orthorhombic with space groups P and P2₁2₁2₁, respectively. All oligomers adopt the well‐known herringbone packing‐mode in crystals with packing parameters dependent on the structure of the end‐capping units and the number of thiophene rings. The shorter intermolecular distance in NaT3 compared to NaT2 indicates that the intermolecular interaction principally increases with increasing molecular length. X‐ray diffraction and atomic force microscopy (AFM) characterization indicate that the NaTn oligomers can form films with better morphology and high molecular order than TNTn oligomers with the same number of thiophene rings. The NaTn oligomers exhibit mobilities that are much higher than those for TNTn oligomers (0.028–0.39 cm² V^–1 s^–1 versus 0.010–0.055 cm² V^–1 s^–1, respectively). In particular, the NaTn oligomers with n = 4–6 all show a mobility higher than 0.1 cm² V^–1 s^–1. This device performance is among the best in aryl end‐capped OThs, and indicates that naphthyl is an effectual building block for designing high‐performance organic semiconducting materials.     

Bulk Inclusions of Pyridazine‐Based Molecular Rotors in Tris(o‐phenylenedioxy)cyclotriphosphazene (TPP)

A new class of rod‐shaped strongly dipolar molecular rotors for insertion into channels of hexagonal tris(o‐phenylenedioxy)cyclotriphosphazene (TPP) has been examined. Seven different 3,6‐disubstituted pyridazines and one singly 3‐substituted system have been prepared and studied by solid‐state nuclear magnetic resonance (NMR), X‐ray powder diffraction, and dielectric spectroscopy. NMR and X‐ray diffraction both show that all but one of these molecular rotors form hexagonal bulk inclusion compounds with TPP. In‐plane lattice parameters for the hexagonal phases increase with the size of the end group, which also controls the energy barriers for rotation of the pyridazine dipole. The barriers range from ≈4 kcal mol^?1 for small or flexible end groups to less than 0.7 kcal mol^?1 for 3‐methylbicyclo[1.1.1]pent‐1‐yl end groups after annealing to 235 °C, and an interpretation of these differences is offered. Computer modeling of the relaxed TPP channels followed by density functional calculation of the environment for one of the rotors provides quantitative agreement with the observed barrier. The systems with the lowest rotational barriers show signs of collective behavior, discussed in terms of antiferroelectric intrachannel and ferroelectric interchannel dipole–dipole interactions. A Curie temperature of 22 K is deduced for 3,6‐diadamant‐1′‐ylpyridazine, but no ordered dielectric phases are found. Conclusions have been drawn for improved rotor design.     

UV‐vis‐Induced Vitrification of a Molecular Crystal

A charge‐transfer complex of 2,5‐dimethyl‐N,N′‐dicyanoquinonediimine (DM) with silver (crystalline Ag(DM)₂, defined as α) is irreversibly transformed by UV‐vis illumination. Depending on the illumination conditions, three new types of solids (defined as γ, δ, and ?) with different structural and physical properties are obtained and examined by a variety of analytical techniques, including solid‐state, high‐resolution, cross‐polarization magic angle spinning (CP‐MAS) ¹³C NMR, elemental analysis (EA), mass spectrometry (MS), X‐ray absorption fine structure (XAFS), and powder X‐ray diffraction (XRD). The CP‐MAS, EA, MS, and XAFS results indicate that compound γ is a glass state of Ag(DM)₂. The transformation from crystalline (α) to amorphous (γ) solid Ag(DM)₂ is an irreversible exothermic glass transition (glass‐transition temperature 155.2 °C; ΔH = –126.8 kJ mol^–1), which implies that the glass form is thermodynamically more stable than the crystalline form. Compound δ (Ag(DM)_1.5) consists of silver nanoparticles (diameter (7 ± 2) nm ) dispersed in a glassy matrix of neutral DM molecules. The ?N–CN–Ag coordination bonds of the α form are not maintained in the δ form. Decomposition of α by intense illumination results in a white solid (?), identified as being composed of silver nanoparticles (diameter (60 ± 10) nm). Physical and spectroscopic (XAFS) measurements, together with XRD analysis, indicate that the silver nanoparticles in both δ and ? are crystalline with lattice parameters similar to bulk silver; however, the magnetic susceptibilities differ from bulk silver.     

p‐CuO/n‐Si heterojunction solar cells with high open circuit voltage and photocurrent through interfacial engineering

Heterojunction solar cells of p‐type cupric oxide (CuO) and n‐type silicon (Si), p‐CuO/n‐Si, have been fabricated using conventional sputter and rapid thermal annealing techniques. Photovoltaic properties with an open‐circuit voltage (V_oc) of 380 mV, short circuit current (J_sc) of 1.2 mA/cm², and a photocurrent of 2.9 mA/cm² were observed for the solar cell annealed at 300 °C for 1 min. When the annealing duration was increased, the photocurrent increased, but the V_oc was found to reduce because of the degradation of interface quality. An improvement in the V_oc resulting to a record value of 509 mV and J_sc of 4 mA/cm² with a high photocurrent of ~12 mA/cm² was achieved through interface engineering and controlling the phase transformation of CuO film. X‐ray diffraction, X‐ray photoelectron spectroscopy, and high‐resolution transmission electron microscopy analysis have been used to investigate the interface properties and crystal quality of sputter‐deposited CuO thin film. The improvement in V_oc is mainly due to the enhancement of crystal quality of CuO thin film and interface properties between p‐CuO and n‐Si substrate. The enhancement of photocurrent is found to be due to the reduction of carrier recombination rate as revealed by transient photovoltage spectroscopy analysis. Copyright © 2014 John Wiley & Sons, Ltd.     

Highly Ordered Mesoporous Silicon Carbide Ceramics with Large Surface Areas and High Stability

Highly ordered mesoporous silicon carbide ceramics have been successfully synthesized with yields higher than 75 % via a one‐step nanocasting process using commercial polycarbosilane (PCS) as a precursor and mesoporous silica as hard templates. Mesoporous SiC nanowires in two‐dimensional (2D) hexagonal arrays (p6m) can be easily replicated from a mesoporous silica SBA‐15 template. Small‐angle X‐ray diffraction (XRD) patterns and transmission electron microscopy (TEM) images show that the SiC nanowires have long‐range regularity over large areas because of the interwire pillar connections. A three‐dimensional (3D) bicontinuous cubic mesoporous SiC structure (Ia3d) can be fabricated using mesoporous silica KIT‐6 as the mother template. The structure shows higher thermal stability than the 2D hexagonal mesoporous SiC, mostly because of the 3D network connections. The major constituent of the products is SiC, with 12 % excess carbon and 14 % oxygen measured by elemental analysis. The obtained mesoporous SiC ceramics are amorphous below 1200 °C and are mainly composed of randomly oriented β‐SiC crystallites after treatment at 1400 °C. N₂‐sorption isotherms reveal that these ordered mesoporous SiC ceramics have high Brunauer–Emmett–Teller (BET) specific surface areas (up to 720 m² g^–1), large pore volumes (～ 0.8 cm³ g^–1), and narrow pore‐size distributions (mean values of 2.0–3.7 nm), even upon calcination at temperatures as high as 1400 °C. The rough surface and high order of the nanowire arrays result from the strong interconnections of the SiC products and are the main reasons for such high surface areas. XRD, N₂‐sorption, and TEM measurements show that the mesoporous SiC ceramics have ultrahigh stability even after re‐treatment at 1400 °C under a N₂ atmosphere. Compared with 2D hexagonal SiC nanowire arrays, 3D cubic mesoporous SiC shows superior thermal stability, as well as higher surface areas (590 m² g^–1) and larger pore volumes (～ 0.71 cm³ g^–1).     

The Influence of the Phase Morphology on the Optoelectronic Properties of Light‐Emitting Electrochemical Cells

We report on the morphological aspects of thin films prepared from a blue–green light‐emitting conjugated polymer, (methyl‐substituted ladder‐type poly(p‐phenylene, mLPPP)), blended with a solid‐state electrolyte composed either by a crown ether, dicyclohexano‐18‐crown‐6 (DCH18C6), or a high‐molecular‐weight poly(ethylene oxide) (HMWPEO), and a Li salt, lithium trifluoromethanesulfonate (LiCF₃SO₃, Li triflate (LiTf)), as they have been successfully applied in light‐emitting electrochemical cells (LECs). The surface morphologies of the blend layers were investigated using atomic force microscopy (AFM) in tapping mode, and the ion distribution was probed using X‐ray analysis by means of energy‐dispersive X‐ray spectrometry (EDXS) in the scanning electron microscope (SEM). We show that the two different phase‐separation processes, the complexation tendencies of the ionic species as well as the ionic transport numbers, have tremendous influence on the performances of the corresponding LECs, revealing either rectifying or symmetric optoelectronic characteristics in forward and reverse bias directions. This opens up new possibilities for tuning the optoelectronic properties of ion‐supported organic electronic devices.