A two-step method combining electrodepositing and spin-coating for solar cell processing

Electrochemistry provides a simple and promising method for preparing organic solar cells (OSCs). In this paper, we present a two-step solution-based method to prepare bilayer heterojunction OSCs by electrodepositing polythiophene (PTh) and then spin-coating chloroform solution of [6,6]-phenyl C61-butyric acid methyl ester (PCBM) onto the PTh layer. The influence of film thickness on performance of bilayer solar cells was investigated, and the best performance was achieved when the thickness of PTh and PCBM was 15 nm and 30 nm, respectively. The optimized solar cell showed power conversion efficiency of 0.1% under the illumination of AM 1.5 (100 mW cm⁻²) simulated solar light. This solution-based method offers a new way for processing bilayer OSCs.     

Synthesis and Characterization of Multi‐Walled Carbon Nanotube/Polythiophene Composites

Multi‐walled carbon nanotube (MWCNT)/polythiophene (PTh) composites have been prepared by in situ chemical oxidative polymerization. PTh is synthesized onto the sidewalls of the MWCNTs, which play a role as hard templates for PTh to produce one‐dimensional nanostructures. The morphology and structures of the MWCNT/PTh composites are characterized by High‐resolution transmission electron microscopy, x‐ray diffraction, and Fourier transform infrared spectrometry. Their electrical property and thermal stability are determined using vector network analyzer and thermal gravimetric analyzer. Moreover, the mechanism of MWCNT/PTh nanowire formation is described. The studies show that the composites are nanowires with core‐shell structure, in which the outer shells and inner cores are formed by PTh and MWCNTs, respectively. The addition of MWCNTs does not change the backbone structure of PTh and affect the amorphous condition of PTh very slightly, however, it improves the electrical conductivity and thermal stability of PTh.     

Polymerization and oxidation of pyrrole by organic electron acceptors

Simultaneous chemical polymerization and oxidation of pyrrole have been initiated by organic electron acceptors, 2,3-dichloro-5,6-dicyano-p-benzoquinone (DDQ) and tetrachloro-o-benzoquinone(chloranil). The polypyrrole (PPY) complexes so produced are semiconductive and granular in nature. For the PPY–DDQ and PPY–chloranil complexes obtained from bulk polymerization, the respective electrical conductivities (σ) are of the order of 10^?1 and 10^?3 ohm^?1 cm^?1. However, σ is substantially lower for the complexes prepared in solvent media. Both complexes are relatively stable in the atmosphere. Thin uniform films of the PPY–organic acceptor complexes have also been synthesized on SnO₂ electrode by electrochemical polymerization in acetonitrile. The physicochemical properties of the PPY–organic acceptor complexes prepared chemically under the various experimental conditions are examined in detail.     

Solid-phase microextraction based on polypyrrole films with different counter ions

Solid-phase microextraction (SPME) fiber coatings based on polypyrrole (PPY) films were prepared by electrochemical deposition of PPY films on platinum wires. To evaluate the effects of counter ions in PPY films on their performance in SPME, PPY films with different counter ions were prepared using different electrolytes during the polymerization processes. The results showed that these PPY films had different extraction properties to the compounds studied due to the different functional groups introduced into the films by the counter ions. Unlike the PPY films formed with small counter ions (such as perchlorate ion) that had anion exchange property, the PPY films having large counter ions such as poly(styrenesulfonate) (PSS) ion showed cation exchange property. Compared with the PPY films having small inorganic counter ions, the PPY films having large organic counter ions, such as dodecylsulphate (DS) ion, showed better extraction efficiency towards nonpolar compounds due to the increased hydrophobic interactions between the compounds and the films. In addition, PPY films formed with large aromatic counter ions had better mechanical stability compared with PPY films with small inorganic counter ions. These films could be applied for SPME of a range of analytes.     

The effect of Nafion ionomer on electroactivity of palladium–polypyrrole catalysts for oxygen reduction reaction

Present studies concentrated on the preparation, characterization, and electroactivity of palladium–polypyrrole (Pd/PPY) catalysts for oxygen reduction reaction. In particular, the effect of Nafion ionomer on their electroactivity was evaluated. In all catalysts prepared by “water-in-oil” microemulsion method, the Pd nanoparticles of ca. 7 nm in size appeared regardless of the Pd content (ranging from 2 to 20 wt.%). For comparison, carbon black-supported (Vulcan XC-72) catalyst (20 wt.% Pd) was also synthesized. Coating of the Pd/PPY samples with Nafion ionomer reduced their surface area and porosity. Chemical interaction due to Nafion acid functionalities affected the N-state of pyrrole as well as electron state of Pd in the Pd/PPY catalysts. As a result, the contribution of more oxidized palladium (Pd^δ+) increased. These interactions played an essential role in the electroactivity of Pd/PPY for oxygen reduction reaction. The increased amount of Nafion relative to that of PPY reduced limiting current density whereas the half-wave potential shifted to a more positive value and the fraction of hydrogen peroxide remarkably decreased.     

Architecture of CuS/PbS heterojunction semiconductor nanowire arrays for electrical switches and diodes

CuS/PbS p-n heterojunction nanowires arrays have been successfully synthesized. Association of template and DC power sources by controllable electrochemistry processes offers a technique platform to efficiently grow a combined heterojunction nanowire arrays driven by a minimization of interfacial energy. The resulting p-n junction materials of CuS/PbS show highly uniform 1D wire architecture. The single CuS/PbS p-n heterojunction nanowire based devices were fabricated, and their electrical behaviors were investigated. The independent nanowires exhibited a very high ON/OFF ratio of 1195, due to the association effect of electrical switches and diodes.     

Synthesis and characterization of conducting polythiophene/carbon nanotubes composites

Conducting polythiophene (PTh)/single‐wall carbon nanotubes (SWNTs) composites were synthesized by the in situ chemical oxidative polymerization method. The resulting cablelike morphology of the composite (SWNT–PTh) structures was characterized with elemental analysis, X‐ray photoelectron spectroscopy, Raman spectroscopy, Fourier transform infrared, ultraviolet–visible spectroscopy, field emission scanning electron microscopy, thermogravimetric analysis, X‐ray diffraction, and transmission electron microscopy. The standard four‐point‐probe method was used to measure the conductivity of the samples. Field emission scanning electron microscopy and transmission electron microscopy analysis revealed that the SWNT–PTh composites were core (SWNTs) and shell (PTh) hybrid structures. Spectroscopic analysis data for the composites were almost identical to those for PTh, supporting the idea that SWNTs served as templates in the formation of a coaxial nanostructure for the composites. The physical properties of the composites were measured and also showed that the SWNTs were modified by conducting PTh with an enhancement of various properties. © 2006 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 44: 5283–5290, 2006     

DC electrical conduction and morphological behavior of counter anion‐governed genesis of electrochemically synthesized polypyrrole films

Highly conducting polypyrrole (PPY) films, doped with various anions [pTS^?, ClO₄^?, and NO₃^? and mixed electrolyte system (pTS^? + ClO₄^?)], have been electrochemically synthesized in aqueous solution at ～275 K in an inert atmosphere. PPY exhibits metallic order dc conductivity at room temperature and shows variation of conductivity with respect to time of polymerization. Effect of dopant anion on growth mechanism of PPY is evident from its surface morphology. X‐ray photoelectron spectroscopy (XPS), used to examine the surface composition and doping level of various PPY films, confirms the anionic doping into the polymer backbone. Both XPS and ultraviolet–visible spectroscopy give evidence of formation of polarons and bipolarons. The temperature (4.2–320 K)‐dependent dc conductivity data of these PPY films have been explained by Mott's 3D variable‐range hopping conduction model. Mott's parameters have been estimated, and structural disorder with doping is correlated for all the samples. Mott's criterion for distant hopping sites prevails in case of moderately doped samples (PPY3, PPY4, and PPY5), whereas the hopping to nearest neighbor sites is found more suitable in case of highly doped samples (PPY1 and PPY2). The origin of these changes is due to the modification in the molecular structure of PPY, which is governed by different growth mechanisms for organic (pTS^?) and inorganic (ClO₄^? and NO₃^?) counter anions. © 2011 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys, 2012     

Observation of Charge Separation and Space‐Charge Region in Single‐Crystal P3HT/C60 Heterojunction Nanowires

We directly observed charge separation and a space‐charge region in an organic single‐crystal p–n heterojunction nanowire, by means of scanning photocurrent microscopy. The axial p–n heterojunction nanowire had a well‐defined planar junction, consisted of P3HT (p‐type) and C₆₀ (n‐type) single crystals and was fabricated by means of the recently developed inkjet‐assisted nanotransfer printing technique. The depletion region formed at the p–n junction was directly observed by exploring the spatial distribution of photogenerated carriers along the heterojunction nanowire under various applied bias voltages. Our study provides a facile approach toward the precise characterization of charge transport in organic heterojunction systems as well as the design of efficient nanoscale organic optoelectronic devices.     

水溶液电化学法制得的聚噻吩的表征

以剖层X光电子能谱(XPS)及红外光指(FTIR)为主要手段对高氯酸水溶液中电化学聚合的聚噻吩进行表征,表明有羰基及键合氯存在,并讨论了聚合过程。     

Syntheses and Optoelectronic Properties of Planar Compounds 3,7‐diaryl‐1,5,2,4,6,8‐dithiotetrazocine

Planar molecules 3,7‐diaryl‐1,5,2,4,6,8‐dithiotetrazocines would be potential acceptor materials of organic solar cell because of their containing SN units. One‐pot synthetic procedures of 3,7‐diaryl‐1,5,2,4,6,8‐dithiotetrazocine compounds are developed to improve their yields up to 2.1–5.9 times as much as those in literatures. The geometries of title compounds were optimized by the density functional theory calculations. Their optoelectronic properties were studied by ultraviolet and cyclic voltammetry spectra and fluorescence quenching experiments. The highest occupied and lowest unoccupied molecular orbital energy level values show that these compounds are suitable to be employed as acceptor materials for developing bulk heterojunction organic solar cells with high open circuit voltages. Emission fluorescence of poly(3‐hexylthiophene) at excited state in dichloromethane was quenched by addition of title compound. Therefore, these compounds used as acceptor materials could exhibit good mobility.     

Uniform Nanowires Containing a Heterogeneousπ-Conjugated Core of Controlled Length,Composition and Morphology

In this work, it is demonstrated for the first time that heterojunction nanowires, consisting of a gradient and segmented-like heterogeneous π-conjugated core with controllable length, composition and morphology, can be generated by co-self-seeding of oligo(p-phenylene vinylene) (OPV)- and oligo(p-phenylene ethynylene) (OPE)-containing block copolymers in spite of different chain lengths and molecular conformation for OPE and OPV. More importantly, based on the understanding of the formation of heterogeneous core by the co-self-seeding approach, a “heating/cooling” seeded growth route was developed, by which linear and branched heterojunction nanowires containing a segmented heterogeneous π-conjugated core of controlled length, composition and morphology can be obtained. This work provides a versatile platform to generate heterojunction nanowires with excellent controllability in length, composition, and morphology.     

Preparation of conducting copolymers by oxidative electropolymerization of 2,2′-bithiophene with pyrrole

Various feed ratios of 2,2′-bithiophene (BT) and pyrrole (PY) were electropolymerized to low conversion and the polymers analyzed for their mer ratios. The polymeric product was rich in polypyrrole (PPY), but the composition could be varied by control of the electrode potential. The increase in BT content is not linear with composition, and the physical evidence indicates oxidative copolymerization and not the formation of the two homopolymers. The data can be interpreted on a copolymerization equation despite the absence of steady state conditions. Sets of reactivity ratios were determined for the polymers formed at two potentials. The electrical efficiencies for polymer formation approach stoichiometric values for oxidative polymerization.     

聚噻吩/多壁碳纳米管复合材料结构与导电机理的研究

从结构和相互作用方面对聚噻吩(PTh)/多壁碳纳米管(MWNTs)复合材料进行了研究, 结果表明: 一方面聚噻吩本身的结构对其导电性能有一定的影响, 另一方面MWNTs作为一种掺杂剂, 和聚噻吩之间存在强的相互作用, 电子从MWNTs转移到聚噻吩. MWNTs和它周围被掺杂的聚噻吩通过π-π共轭作用形成相对独立的导电单元, 在复合材料的导电体系中起到主要作用, 随着这种导电单元数量的增加直至相互接触, 形成大的导电体系, 复合材料的电导率达到最大值.     

Stimulus‐Responsive Metal–Organic Frameworks

Materials that can recognize the changes in their local environment and respond by altering their inherent physical and/or chemical properties are strong candidates for future “smart” technology materials. Metal–organic frameworks (MOFs) have attracted a great deal of attention in recent years owing to their designable architecture, host–guest chemistry, and softness as porous materials. Despite this fact, studies on the tuning of the properties of MOFs by external stimuli are still rare. This review highlights the recent developments in the field of stimulus‐responsive MOFs or so‐called smart MOFs. In particular, the various stimuli used and the utility of stimulus‐responsive smart MOFs for various applications such as gas storage and separation, sensing, clean energy, catalysis, molecular motors, and biomedical applications are highlighted by using representative examples. Future directions in the developments of stimulus‐responsive smart MOFs and their applications are proposed from a personal perspective.     

New pyrrolopyridazine derivatives as blue organic luminophors

New pyrrolopyridazine derivatives were synthesized as potential blue organic luminophors. Three different classes of pyrrolopyridazine derivatives were made, for example, aryl groups directly connected to the core PPY (pyrrolo[1,2-b]pyridazine-5,6,7-tricarboxylic acid trimethyl ester) moiety, aryl groups connected to the PPY via a vinylene linker and aryl groups connected to the PPY via an acetylene linker. Their optical and electrochemical properties were productively compared. One of the derivatives 2 showed a relative quantum yield as high as 0.9. Compound 8 in the vinyl bridged pyrrolopyridazine series has been characterized by its X-ray crystal structure analysis.     

Self‐Assembled 1D‐Nanowire Lasers of Perylenediimides

The 1D nanostructures of perylenediimides (PDIs) have been readily obtained owing to strong cofacial π–π stacking interactions, which, however, subsequently render PDIs weakly emissive in the solid state. Therefore, organic solid‐state lasers based on 1D nanostructures of PDIs have not been achieved yet. Herein, we prepared 1D‐nanowires of N,N’‐bis(1‐ethylpropyl)‐2,5,8,11‐tetrakis(o‐methylphenyl)‐perylene‐3,4:9,10‐tetracarboxylic acid diimide (mp‐PDI), which stack into a loosely J‐type arrangement. J‐aggregation leads to a solid‐state photoluminescence (PL) efficiency φ>18 % and the nanowires of mp‐PDI exhibit excellent Fabry–Perot (FP) mode laser action.     

Temperature dependence of the field effect mobility of solution-grown germanium nanowires

The temperature dependence of the field effect mobility was measured for solution-grown single-crystal Ge nanowires. The nanowires were synthesized in hexane from diphenylgermane by the supercritical fluid-liquid-solid process using gold nanocrystals as seeds. The nanowires were chemically treated with isoprene to passivate their surfaces. The electrical properties of individual nanowires were then measured by depositing them on a Si substrate, followed by electrical connection with Pt wires using focused ion beam assisted chemical vapor deposition. The nanowires were positioned over TaN or Au electrodes covered with ZrO2 dielectric that were used as gates to apply external potentials to modulate the conductance. Negative gate potentials increased the Ge nanowire conductance, characteristic of a p-type semiconductor. The temperature-dependent source/drain current-voltage measurements under applied gate potential revealed that the field effect mobility increased with increasing temperature, indicating that the carrier mobility through the nanowire is probably dominated either by a hopping mechanism or by trapped charges in fast surface states.     

Solar-Powered Organic Semiconductor–Bacteria Biohybrids for CO2 Reduction into Acetic Acid

An organic semiconductor–bacteria biohybrid photosynthetic system is used to efficiently realize CO₂ reduction to produce acetic acid with the non-photosynthetic bacteria Moorella thermoacetica. Perylene diimide derivative (PDI) and poly(fluorene-co-phenylene) (PFP) were coated on the bacteria surface as photosensitizers to form a p-n heterojunction (PFP/PDI) layer, affording higher hole/electron separation efficiency. The π-conjugated semiconductors possess excellent light-harvesting ability and biocompatibility, and the cationic side chains of organic semiconductors could intercalate into cell membranes, ensuring efficient electron transfer to bacteria. Moorella thermoacetica can thus harvest photoexcited electrons from the PFP/PDI heterojunction, driving the Wood–Ljungdahl pathway to synthesize acetic acid from CO₂ under illumination. The efficiency of this organic biohybrid is about 1.6 %, which is comparable to those of reported inorganic biohybrid systems.     

Bamboo-shaped Ag-doped TiO2 nanowires with heterojunctions

Bamboo-shaped Ag-doped TiO2 nanowires with heterojunctions were synthesized by a simple solvothermal method. The diameter of the nanowires was about 50-100 nm, and they had a length of up to a few millimeters. The detailed structure of the heterojunction in the nanowire was also characterized.