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Tribochemistry, which is another name of mechanochemistry driven by shear, deals with complex and dynamic interfacial processes that can lead to facilitation of surface wear or formation of beneficial tribofilms. For better mechanistic understanding, we investigated the reactivity of tribopolymerization of organic molecules with different internal ring strain energy (methylcyclopentane, cyclohexane, and cyclohexene) on a stainless steel (SS) surface in inert (N2), oxidizing (O2), and reducing (H2) environments. On the clean SS surface, precursor molecules were found to physisorb with a broad range of molecular orientations. In inert and reducing environments, the strain-free cyclohexane showed the lowest tribochemical activity among the three tested. Compared to the N2 environment, the tribochemical activity in H2 was suppressed. In the O2 environment, only cyclohexene produced tribofilms and methylcyclopentane and cyclohexane did not. When tribofilms were analyzed with Raman spectroscopy, the spectral features of diamond-like carbon (DLC) or amorphous carbon (a-C) were observed due to photochemical degradation of triboproducts. Based on infrared spectroscopy, tribofilms were found to be organic polymers containing oxygenated groups. Whenever polymeric tribrofilms were produced, wear volume was suppressed by orders of magnitudes but not completely to zero. These results supported the previously suggested mechanisms which involved surface oxygens as a reactant species of the tribopolymerization process.

Many previous studies of tribofilms have interpreted D- and G-bands in Raman spectra as evidence that diamond-like carbon (DLC) was formed during sliding. DLC and other amorphous-carbon films are produced by high-energy processes or high-temperature pyrolysis. Since neither of these conditions commonly occurs in a sliding interface, it seems unlikely that such materials could be produced during simple frictional sliding. To understand this apparent contradiction, we systematically analyzed tribofilms produced from vapor and liquid lubrication experiments using Raman spectroscopy with varied laser power and wavelength. The results provide evidence that DLC-like features in Raman spectra of tribofilms formed from organic molecules originate, not by tribochemical synthesis in situ during the tribo-testing as suggested previously, but rather from post-synthesis photochemical degradation of carbonaceous organic matter during the Raman analysis.

Cathode interfacial layers (CIL) have been applied in organic solar cells (OSCs) for the enhancement of photovoltaic characteristics. Most of them are employed in either conventional organic solar cells (COSCs) or inverted organic solar cells (IOSCs) only. Herein, we have designed and synthesized two cathode interfacial materials, namely, 3-(4,6-bis(4-bromophenoxy)-1,3,5-triazin-2-yl)-2,6-difluorophenyl)diphenylphosphine oxide (Br-PO-TAZ) and 4,4′-((6-(3-(diphenylphosphoryl)-2,4-difluorophenyl)-1,3,5-triazine-2,4-diyl)bis(oxy))dibenzonitrile (CN-PO-TAZ), and utilized them as CILs for both COSCs and IOSCs. The incorporation of our new CIL layers significantly enhanced the photovoltaic performance compared to COSCs and IOSCs without the CILs. The CN-PO-TAZ exhibited a power conversion efficiency (PCE) of 8.19% for COSCs and 8.33% for IOSCs, whereas Br-PO-TAZ yielded a PCE of 8.15% for COSCs and 8.23% for IOSCs, respectively. The improved performance was attributed to the multiple favorable factors: significantly reducing leakage current, decreasing series resistance, suppressing recombination, efficient charge transport and collection. Moreover, the CIL layers helped for sustaining device stability because they served as an internal shield against humidity.

In this study, the performance of a multi-split VRF system using the bypass cycle and injection cycle is evaluated using the numerical simulation as a possible sub-cooling method to prevent flash gas generation in liquid pipelines. The simulation for the multi-split VRF system is developed by considering the applications of the bypass cycle and injection cycle, and is validated with experimental data. The bypass cycle and injection cycle in the multi-split VRF system yield improvements in their cooling capacities of the order of 3.22% and 13.43%, respectively, and energy efficient ratio (EER) of the order of 1.98% and 1.72%, respectively. The input power of the injection cycle is reduced by up to 4.45% when the performance of the multi-split VRF systems with bypass cycle and injection cycle is compared under the same cooling capacity conditions.

The formation of stabilized radical anions on organic materials in the solid state is an important issue in radical-based fundamental research and various applications. Herein, for the first time, we report on gas-induced ion-free stable radical anion formation (SRAF) of organic semiconducting solids with high gas selectivities through the use of organic field-effect transistor (OFET) gas sensors and electron spin resonance spectroscopy. In contrast to the previously reported SRAF, which requires either anionic analytes in solution and/or cationic substituents on π-electron-deficient aromatic cores, NDI-EWGs consist of an n-type semiconducting naphthalene diimide (NDI) and various electron-withdrawing groups (EWGs) that exhibit non-ion-involved, gas-selective SRAF in the solid state. In the presence of hard Lewis base gases, NDI-EWG-based OFETs exhibit enhanced conductivity (Current-ON mode) through the formation of an SRAF NDI/gas complex, while in the presence of borderline and soft Lewis base gases, NDI-EWG-based OFETs show decreased conductivity (Current-OFF mode) by the formation of a resistive NDI/gas complex. Organic semiconducting solids with EWGs exhibiting highly gas-selective solid-SRAF constitute a very promising platform for radical-based chemistry and can be used in various applications, such as highly gas-selective probes.

Amine-functionalized graphene was synthesized via a one-step solvothermal method and used as a metal-free cathode for non-aqueous lithium–oxygen batteries. The material delivered an outstanding specific capacity of 19,789 mAh/g at a current density of 200 mA/g as well as better cycling stability than graphene without the amine functional group. This improvement was attributed to the electron-donating effect of the amine groups and appropriate mesopore volume, which can promote the penetration of oxygen, electrons, and lithium ions, as well as accommodate more discharge products, Li2O2 in Li–O2 batteries. Amine-functionalized graphene has an amine functional group on the carbon surface, which improves the electrical conductivity of carbon and provides electrochemical active sites for oxygen absorption reactions.

The performance of the variable refrigerant flow (VRF) system becomes poor at a very low ambient temperature because of the decrease in the suction mass flow rate. The vapor injection is applied to the heat pump system to enhance the performance of the systems in a cold season. In this study, the influence of the vapor injection under different intermediate pressures and outdoor ambient temperatures was investigated mathematically, and the results were validated with experimental data. In addition, the performance variation was observed with different indoor ambient temperatures in nine indoor units. The intermediate pressure affected the heating capacity, input power, coefficient of performance (COP), and isentropic efficiency of the compressor. The improvement of the COP with vapor injection was dominant at a low ambient temperature. The heating capacity at different indoor ambient temperatures was observed with different refrigerant mass flow rates in each indoor unit.

High-level heteroatom, N and S, dual-doped graphene with an improved mesoporous structure was fabricated via facile in situ carbonization and used as metal-free cathode for non-aqueous lithium oxygen batteries. The prepared cathode delivered an ultrahigh specific capacity of 22,252 mAh/g at a current density of 200 mA/g as well as better cycling reversibility because of the larger and copious mesopores, which can promote the penetration of oxygen, electrons, and lithium ions and the ability to accommodate more discharge products, e.g., Li2O2, in Li–O2 batteries. The material had a high level of heteroatom co-doping in the carbon lattice, which enhanced the electrical conductivity and served as active sites for the oxygen reduction reaction.

Novel hole blocking materials (HBMs) based on 2,6-disubstituted dibenzo[b,d]furan and dibenzo[b,d]thiophene segments, 3,3′,3′′,3′′′-(dibenzo[b,d]furan-2,6-diylbis(benzene-5,3,1-triyl))tetrapyridine (26DBFPTPy) and 3,3′,3′′,3′′′-(dibenzo[b,d]thiophene-2,6-diylbis(benzene-5,3,1-triyl))tetrapyridine (26DBTPTPy), are successfully designed and synthesized for high-performance blue phosphorescent organic light-emitting diodes (PhOLEDs) for the first time. Computational simulation is used to investigate the optimal structure, orbital distribution, and physicochemical properties of both molecules. Thermal, optical, and electrochemical analysis shows that 26DBFPTPy and 26DBTPTPy possess high thermal stability, deep HOMO energy levels (−7.08 and −6.91 eV), and a high triplet energy (ET) (2.75 and 2.70 eV). Blue PhOLEDs with 26DBFPTPy or 26DBTPTPy as a hole blocking layer (HBL) exhibit a low turn-on voltage (3.0 V) and operating voltage (4.5 V) at 1000 cd m−2. In addition, the blue PhOLEDs with 26DBFPTPy or 26DBTPTPy show superior external quantum efficiencies (24.1 and 23.6%) and power efficiencies (43.9 and 42.7 lm W−1). They also show a very small efficiency roll-off of about 8.5% from 100 to 1000 cd m−2. Furthermore, they exhibit improved lifetimes compared to the similarly designed HBL with a pyridine electron transport unit and a phenyl core structure.

Novel hole blocking materials (HBMs) based on dibenzo[b,d]furan and dibenzo[b,d]thiophene molecular dimers have been rationally designed and synthesized for high-efficiency and long-lived blue phosphorescent organic light-emitting diodes (PhOLEDs). Thermal, optical, and electrochemical analyses show that [2,2′-bidibenzo[b,d]furan]-6,6′-diylbis(diphenylphosphine oxide) (DBF-d-PO), [2,2′-bidibenzo[b,d]thiophene]-6,6′-diylbis(diphenylphosphine oxide) (DBT-d-PO), 6,6′-di(pyridine-3-yl)-2,2′-bidibenzo[b,d]furan (DBF-d-Py), and 6,6′-di(pyridine-3-yl)-2,2′-bidibenzo[b,d]thiophene (DBT-d-Py) possess high thermal stability, deep highest occupied molecular orbital energy levels (−6.61 to −6.95 eV), and high triplet energy (ET) (2.68–2.95 eV). Blue PhOLEDs with DBF-d-PO, DBT-d-PO, DBF-d-Py, and DBT-d-Py exhibit low turn-on and operating voltages, excellent external quantum efficiency, and high current and power efficiencies. A blue PhOLED with DBF-d-Py shows the best efficiency with a maximum external quantum efficiency of 24.3%, a maximum current efficiency of 44.3 cd A−1, and a maximum power efficiency of 46.4 lm W−1. In addition, it exhibits an outstanding external quantum efficiency of 22.4% at a practical luminance of 1000 cd m−2 and a very high maximum luminance of 88 953 cd m−2 at 12 V. Furthermore, blue PhOLEDs with DBF-d-Py and DBT-d-Py exhibit highly improved lifetimes compared with the conventional HBM, BmPyPB, because of the efficient hole blocking by the deep HOMO energy level and the high thermal stability stabilizing hole blocking layer morphology.

This study describes a systematic study on side chain effect in the poly(thieno[3,4-b]thiophene)benzo[1,2-b:4,5-b′]dithiophene (PTB) polymer series based regioregular polymers with D1-A-D2-A configuration, denoted as PTT-BDT(R1)-TT-BDT(R2). The synthesized three regioregular polymers employ the same conjugated backbone but with different side chains (R1, R2), P1; hexyldecyl thiophene (HD, R1) and ethylhexyl thiophene (EH, R2), P2; hexyldecyl thiophene (HD, R1) and ethylhexylthio thiophene (S-EH, R2), P3; hexyldecylthio thiophene (S-HD, R1) and ethylhexylthio thiophene (S-EH, R2). Introduction of different side chains influenced optical, electrochemical, molecular packing properties, and device performance. The P3 polymer with alkylthio thiophene groups as R1 and R2 showed much broader light absorption and lower HOMO level than other polymers with relatively less alkylthio thiophene groups. Furthermore, the P3 polymer exhibited favorable polymer orientation and short π-π stacking distance for efficient charge transport in the BHJ PSCs. The P3 based bulk-heterojunction (BHJ) polymer solar cell (PSC) showed an improved PCE of 7.20% while the P1 and P2 based BHJ PSC devices showed PCEs of 5.27% and 6.45%, respectively. This result, within our knowledge, is the highest record among BHJ PSCs based PTB polymer series composed of benzo[1,2-b:4,5-b’]dithiophene (BDT) segment and non-fluorinated alkyl ester (COOR) side chain substituted thieno[3,4-b]thiophene (TT) segment.

A series of highly microporous carbon materials was produced by carbonization of a triazine-based covalent organic polymer (TCOP) followed by carbonization and CO2 physical activation. The N-containing porous COP was prepared from easily available economic monomer precursors via a simple Friedel-Crafts reaction, which produced a predominantly microporous structure with a high surface area. Carbonization at 600–900 °C produced predominantly microporous carbons with a narrow pore size distribution in the range of 0.5–1.5 nm. Upon further activation using CO2, more micropores were formed, accompanied by an increase in the surface area (to 2003 m2 g−1) and the nitrogen level in the carbon structure was maintained at ca. 2 wt%. The electrochemical properties of the samples were measured by employing a three-electrode system with 6 M KOH electrolyte. Among the prepared carbon samples, the electrode fabricated using the carbon activated at 900 °C (AC-900) had a specific capacitance of 278 F g−1 at a current density of 1 A g−1, which is significantly higher than that of a commercial activated carbon (130 F g−1) and ranks among the highest reported so far. This improved performance was attributed to the highly microporous structure of the nitrogen-doped carbon with a narrow pore size distribution.

We designed and synthesized new hole-blocking materials (HBMs), mPyrPPB and pPPyrPB, consisting of pyrimidine and phenylene segments for high-performance blue phosphorescent OLEDs. The thermal, electrochemical, and optical properties of mPyrPPB and pPPyrPB were systemically investigated. It was found that the Tg values of mPyrPPB and pPPyrPB were 118 and 137 °C, respectively. Especially, the triplet energy and highest occupied molecular orbital (HOMO) energy level of mPyrPPB were 2.77 eV and −6.86 eV, respectively, indicating that it had sufficiently high triplet energy and deep HOMO energy level for the hole-blocking layer (HBL) in blue phosphorescent OLED devices. It was found that all the meta conjugation of mPyrPPB molecular structure effectively prevented π-electron delocalization and thus increased the triplet energy and electron transport property. In addition, mPyrPPB exhibited higher electron-transporting property than pPPyrPB because mPyrPPB possessed effective intermolecular hydrogen bonds. When mPyrPPB was utilized as a HBM for a blue phosphorescent OLED device, external quantum efficiency (EQE), current efficiency (CE), and power efficiency (PE) values effectively increased to 16.4%, 36.7 cd/A, and 13.4 lm/W, respectively. Compared to the reference device without HBM, EQE, CE, and PE increased by 38%, 35%, and 54% respectively, mainly due to the confinement of triplet excitons and holes and improved electron-transporting ability.

Herein, 3D in-situ hollow carbon fiber/carbon nanosheet/Fe3C@Fe3O4 (h-CNF/CNS/Fe3C@Fe3O4) was constructed using ferrocene and oleic acid by a solventless one-step process that did not require additional filtering, neutralization, drying, or calcination steps. The iron-oleate chelating structure that self-assembled during annealing facilitated the fabrication of 3D in-situ h-CNF/CNS/Fe3C@Fe3O4 by undergoing graphitization at 600 °C. This carbon shell of the 3D in-situ h-CNF/CNS/Fe3C@Fe3O4 was derived from the two cyclopentadienyl rings in ferrocene. This hybrid material made from economically cheap oleic acid exhibited superior supercapacitive behavior: high specific capacitance of 327 F g−1 at 5 mV s−1 and 210 F g−1 at 10 mV s−1, good rate capability of 60 F g−1 at 10 A g−1 (compared to 70 F g−1 at 1 A g−1 for pure Fe3O4), and superior retention of 108% after 6000 cycles at 100 mV s−1. These superior supercapacitive properties were ascribed to the 3D graphitic h-CNF/CNS for enhancing electrical conductivity and the carbonaceous shell over Fe3C@Fe3O4 core for buffering the bulk expansion of iron-related particles.

Aligned carbon nanofibers (ACNFs) were fabricated by electrospinning using a high speed of rotary collector (2000 rpm). To achieve a synergy effect of the electron double layer and redox faradaic reaction, NiCo 2 O 4 was deposited on the surface of the ACNFs using an electrodeposition method. The improved electrochemical performance of the electrodes was investigated by cyclic voltammetry, galvanostatic charge-discharge testing, and electrochemical impedance analysis. Among the prepared electrodes, which were deposited for different times (5, 10, 20, and 30 s), the sample deposited by NiCo 2 O 4 for 10 s had the highest specific capacitance (90.1 F g −1 at 5 mV s −1 ), good rate capability (64.7%), and cycle stability (85.2% after 1000 cycles). In addition, to examine the effects of the alignment and redox faradaic reaction of NiCo 2 O 4, the ACNFs covered with NiCo 2 O 4 for 10 s (NC-ACNFs) were compared with the ACNFs deposited by Co 3 O 4 (C-ACNFs) and randomly oriented carbon nanofibers covered with NiCo 2 O 4 (NC-RCNFs) . The NC-ACNFs had a 15.8% and 11.3% higher specific capacitance than that of the C-ACNFs and NC-RCNFs, respectively. These results suggested that the electrochemical properties of carbon nanofibers could be improved through the structural effects of aligned nanofibers and a redox faradaic reaction of NiCo 2 O 4 .

A regioregular D1-A-D2-A terpolymer PDTSTTBDT incorporating dithieno[3,2-b:2′,3′-d]silole (DTS, D1) and benzo[1,2-b:4,5-b]dithiophene (BDT, D2) units with perfectly controlled thieno[3,4-b]thiophene (TT, A) orientation was synthesized for the first time. The thermal, optical, and electrochemical properties of the regioregular PDTSTTBDT were characterized and compared with the random PDTSTTBDT without structural regioregularity. The regioregular PDTSTTBDT showed ideal optical bandgap (1.45 eV), lower lying HOMO energy level, and higher degree of crystallinity compared to the random PDTSTTBDT. Moreover, it exhibited excellent solubility in nonhalogenated solvents as well as halogenated solvents. The inverted bulk-heterojunction polymer solar cells (PSCs) based on the regioregular PDTSTTBDT and o-xylene process solvent showed a power conversion efficiency as high as 6.14%, which is 500% higher than the random PDTSTTBDT-based PSCs. It was found that the remarkable enhancement of photovoltaic performance in re...

Terpolymers consisting of three monomers with one electron donor unit and two electron acceptor units are promising p-type polymers for polymer solar cells (PSCs) because the incorporation of a third monomer into a copolymer backbone provides synergetic effect on physical properties such as absorption ability, charge transport, and photovoltaic performance. Currently, novel p-type terpolymers need to be developed for high-efficiency PSCs, which can be processed with eco-friendly non-halogenated solvents. In this study, a new series of terpolymers composed of 4,8-di(2,3-didecylthiophen-5-yl)-benzo[1,2-b:4,5-b′]dithiophene (BDT), 4,7-di(thien-2-yl)-5,6-difluoro-2,1,3-benzothiadiazole (DTffBT), and benzo[1,2-c:4,5-c′]dithiophene-4,8-dione (BDD) segments was synthesized and characterized for high-performance PSCs processed with non-halogenated solvents. PBDTBD terpolymers (i.e., PBDTBD-25, PBDTBD-50, and PBDTBD-75) were synthesized by adjusting different ratios of DTffBT to BDD segment (25%, 50%, and 75% of DTffBT). PBDTBD terpolymers exhibited excellent solubility in non-halogenated solvents. The optical, electrochemical, and morphological properties of PBDTBD terpolymers were successfully controlled by modulating the molar ratio of DTffBT and BDD. Moreover, a PBDTBD-50:IT-4F blended film showed homogeneous film with a favorable face-on orientation. The PBDTBD-50:IT-4F blended film showed excellent hole and electron mobility, which resulted in a superior carrier balance. PBDTBD-50-based PSCs, processed with o-xylene, achieved the highest PCE of 10.03%, which is four times higher than those of copolymer-based PSCs. The novel terpolymers composed of one electron donor unit and two electron acceptor units are expected to make a considerable contribution to the development of high-performance PSCs.

Many researchers have reported dibenzo[b,d]furan segment as a building block of organic light-emitting diode (OLED) materials because it has high thermal stability and triplet energy. However, most of the research has focused on symmetrically substituting the same functional groups at 2-position due to easy functionalization or substituting the same functional groups at different positions of dibenzo[b,d]furan. Herein, we design and synthesize three new hole blocking materials based on asymmetrically difunctionalized dibenzo[b,d]furan, diphenyl (2-(pyridin-3-yl)dibenzo[b,d]furan-6-yl)phosphine oxide (DBFPO-Py), diphenyl(2-(pyrimidin-5-yl)dibenzo[b,d]furan-6-yl)phosphine oxide (DBFPO-Pyr), and diphenyl(2-(4-(triphenylsilyl)phenyl)dibenzo[b,d]furan-6-yl)phosphine oxide (DBFPO-Si) for high-performance phosphorescent OLEDs. Phosphine oxide, tetraphenylsilane, pyridine, and pyrimidine segments are successfully introduced into the asymmetric position of a dibenzo[b,d]furan. It is found that DBFPO-Py, DBFPO-Pyr, and DBFPO-Si possess high thermal stability; high triplet energies of 2.96, 2.98, and 2.80 eV; and deep highest occupied molecular orbital (HOMO) energy levels of −7.13, −7.23 and −7.07 eV; respectively. Blue phosphorescent OLEDs with DBFPO-Py, DBFPO-Pyr, and DBFPO-Si show low turn-on voltages, high current and power efficiencies, and superior external quantum efficiencies. Blue phosphorescent OLEDs with DBFPO-Py and DBFPO-Pyr showed improved performance in terms of current and power efficiencies, etc, compared with the device with 1,3-bis(3,5-dipyrid-3-yl-phenyl)benzene (BmPyPB), which is commonly used as a hole blocking layer. More importantly, the blue phosphorescent OLEDs with DBFPO-Pyr showed the best performance with maximum external quantum efficiency of 23.6%, current efficiency of 29.8 cd A−1, power efficiency of 26.0 lm W−1, and low efficiency roll-off of 6.38%. Novel hole blocking materials based on asymmetrically difunctionalized dibenzo[b,d]furan are expected to make a significant contribution to the development of blue phosphorescent OLEDs.

E-mail: chk@inha.ac.krReceived August 29, 2011, Accepted September 19, 2011Key Words : DSSCs, Dye-sensitized solar cells, High efficiency, DinaphthylphenylamineRecently, dye-sensitized solar cells (DSSCs) have at-tracted great attention because they have advantages inconverting solar energy to electrical energy at low cost. Oneof the key issues in high performance DSSCs is the rationaldesign of the photosensitizers, which can exhibit high solar-to-energy conversion efficiency. The Ru complex photo-sensitizers such as N3, N719 and Black dye exhibit effi-ciencies about 11% under AM 1.5G irradiation.

Ti-HMS samples in which titanium species exist in various forms of isolated tetrahedral state, finely dispersed TiO 2 cluster, and some in extra-framework anatase phase were prepared via a direct synthesis route using dodecylamine (DDS) as a structure directing agent by systematically varying the titanium loadings between 2 and 50 mol% Ti/(Ti+Si) in substrate composition. Physicochemical properties of the materials were evaluated using XRD, SEM/TEM, N 2 adsorption, UV-vis and XANES spectroscopies. Catalytic properties of Ti-HMS in cyclohexene and 2,6-di-tert-butyl phenol (2,6-DTBP) oxidation using aqueous H 2 O 2 , and vapor phase photocatalytic degradation of acetaldehyde were evaluated. High H 2 O 2 selectivity was obtained in cyclohexene oxidation, and cyclohexene conversion was found primarily dependent on the amount of tetrahedrally coordinated Ti sites. For bulky 2,6-DTBP oxidation and photocatalytic oxidation of acetaldehyde, on the other hand, conversions were found dependent on the total amount of Ti sites and maintaining an uniform mesoporous structure in the catalysts was not critical for efficient catalysis.