Dibenzothiophene-Substituted Fullerene Derivative as Electron Acceptor for Polymer Solar Cells.

A new fullerene derivative, [6,6]-dibenzo[b,d]thiophene-C61-butyric acid methyl ester (DBTC61BM) was synthesized from C60 using tosylhydrazone, and used as an electron-acceptor material for poly(3-hexylthiophene) (P3HT)-based organic photovoltaic cells. The synthesized DBTC61BM was used to modify the basic structure of [6,6]-phenyl-C61-butyric acid methyl ester (PC61BM) by replacing the aromatic part with dibenzo[b,d]thiophene. The solubilities of DBTC61BM and PC61BM are similar; they have good solubilities in common organic solvents such as dichloromethane, chloroform, toluene, and 1,2-dichlorobenzene. The Stern-Volmer quenching constant (K(sv)) of DBTC61BM was 7.14 x 10(3) M(-1), and was correlated with the binding affinity between the fluorophore and a quencher. The lowest unoccupied molecular orbital energy level of DBTC61BM was -3.71 eV. The charge-carrier mobility of a P3HT:DBTC61BM blend film was determined using the space-charge-limited current method; the electron mobility value obtained for the P3HT:DBTC61BM blend film was 2.13 x 10(-4) cm2 V(-1) s(-1). Photovoltaic devices were fabricated using P3HT as the electron donor and DBTC61BM as the electron acceptor. Among the fabricated devices, photovoltaic cells with the structure ITO/PEDOT:PSS/P3HT:DBTC61BM/LiF/Al showed the highest power conversion efficiency, namely 3.23%, with an open-circuit voltage of 0.64 V, short-circuit-current density of 8.14 mA cm(-2), and fill factor of 0.59, under AM 1.5 G (100 mW cm(-2)) illumination.

A New Lridium(III) Complex as a Deep-Red Phosphorescent Emitter in Organic Light-Emitting Diodes.

We synthesized a novel red-emitting iridium(III) complex, bis[2-(5-(9H-carbazole-9-yl)thiophene-2-yl)benzo[d]thiazole]iridium(III)acetylacetonate ([(CTBT)21 r(acac)]), for use in phosphorescent organic light-emitting diodes. The photophysical and electrochemical properties of [(CTBT)2Ir(acac)] were characterized using photoluminescence (PL) and cyclic voltammetry. The photophysical properties of [(CTBT)2Ir(acac)] included PL emission at 630 nm. The highest occupied molecular orbital (HOMO) and lowest unoccupied molecular orbital (LUMO) energy levels of [(CTBT)2Ir(acac)] were calculated to be -5.14 and -2.83 eV, respectively. Phosphorescent organic light-emitting diodes with a configuration of ITO/PEDOT:PSS (30 nm)/TAPC (30 nm)/TPBi (12.5 nm):TCTA (12.5 nm):dopant (3%, 5%, 10%)/TSPO1 (35 nm)/LiF (1 nm)/Al (100 nm) were fabricated and characterized. The fabricated device doped with 5% [(CTBT)2Ir(acac)] showed a high luminous efficiency of 2.06 cd/A, maximum external quantum efficiency of 4.32% at 4 V, maximum outstanding luminance of 398.8 cd/m2, and maximum power efficiency of 1.79 lm/W with Commission Internationale de L'Eclairage (CIE) coordinates of (0.69, 0.31).

Naphthalene-, anthracene-, and pyrene-substituted fullerene derivatives as electron acceptors in polymer-based solar cells.

A series of aryl-substituted fullerene derivatives were prepared in which the aromatic moiety of [6,6]-phenyl C61-butyric acid methyl ester (PC61BM) was modified by replacing the monocyclic phenyl ring with bicyclic naphthalene (NC61BM), tricyclic anthracene (AC61BM), and tetracyclic pyrene (PyC61BM). The PC61BM derivatives were synthesized from C60 using tosylhydrazone and were tested as electron acceptors in poly(3-hexylthiophene) (P3HT)-based organic photovoltaic cells (OPVs). The lowest unoccupied molecular orbital (LUMO) energy level of NC61BM (-3.68 eV) was found to be slightly higher than those of PC61BM (-3.70 eV), AC61BM (-3.75 eV), and PyC61BM (-3.72 eV). The electron mobility values obtained for the P3HT:PC61BM, P3HT:NC61BM, P3HT:AC61BM, and P3HT:PyC61BM blend films were 2.39 × 10(-4), 2.27 × 10(-4), 1.75 × 10(-4), and 2.13 × 10(-4) cm(2) V(-1) s(-1), respectively. P3HT-based bulk-heterojunction (BHJ) solar cells were fabricated using NC61BM, AC61BM, and PyC61BM as electron acceptors, and their performances were compared with that of the device fabricated using PC61BM. The highest power conversion efficiencies (PCEs) observed for devices fabricated with PC61BM, NC61BM, AC61BM, and PyC61BM were 3.80, 4.09, 1.14, and 1.95%, respectively, suggesting NC61BM as a promising electron acceptor for OPVs.

Fullerene derivatives as electron acceptors for organic photovoltaic cells.

Energy is currently one of the most important problems humankind faces. Depletion of traditional energy sources such as coal and oil results in the need to develop new ways to create, transport, and store electricity. In this regard, the sun, which can be considered as a giant nuclear fusion reactor, represents the most powerful source of energy available in our solar system. For photovoltaic cells to gain widespread acceptance as a source of clean and renewable energy, the cost per watt of solar energy must be decreased. Organic photovoltaic cells, developed in the past two decades, have potential as alternatives to traditional inorganic semiconductor photovoltaic cells, which suffer from high environmental pollution and energy consumption during production. Organic photovoltaic cells are composed of a blended film of a conjugated-polymer donor and a soluble fullerene-derivative acceptor sandwiched between a poly(3,4-ethylenedioxythiophene):poly(styrenesulfonate)-coated indium tin oxide positive electrode and a low-work-function metal negative electrode. Considerable research efforts aim at designing and synthesizing novel fullerene derivatives as electron acceptors with up-raised lowest unoccupied molecular orbital energy, better light-harvesting properties, higher electron mobility, and better miscibility with the polymer donor for improving the power conversion efficiency of the organic photovoltaic cells. In this paper, we systematically review novel fullerene acceptors synthesized through chemical modification for enhancing the photovoltaic performance by increasing open-circuit voltage, short-circuit current, and fill factor, which determine the performance of organic photovoltaic cells.

(E)-2,2'dibromo-7,7'-bis(diphenylamino)-9,9' bifluorenylidene as a new electron acceptor for organic photovoltaic cells.

(E)-2,2'-Dibromo-7,7'-bis(diphenylamino)-9,9'-bifluorenylidene (BDPABF) was synthesized as a new non-fullerene-type electron acceptor for organic photovoltaic cells. The UV-visible absorption spectra of BDPABF showed two main bands at 319 and 474 nm in a chloroform solution and 320 and 481 nm as a solid thin film. The optical band gap of BDPABF was determined to be 2.34 eV by measuring the onset absorption wavelength of the solid thin film. The ionization potential of BDPABF was determined to be 5.59 eV using photoelectron spectroscopy. The measured lowest unoccupied molecular orbital energy level of BDPABF was - 3.25 eV. Its electron-accepting ability was investigated through a Stern-Volmer quenching experiment. The intensity of the photoluminescence of P3HT dramatically decreased upon the addition of BDPABF. The measured Stern-Volmer quenching constant was 5.3 x 10(4) M(-1). Photovoltaic devices were fabricated using P3HT as the electron donor and BDPABF as the electron acceptor at various composition ratios. The optimized device showed a maximum power conversion efficiency of 0.27% with an open-circuit voltage of 0.71 V, short-circuit current density of 1.29 mA/cm2, and fill factor of 0.29 after thermal annealing at 100 degrees C for 5 min.

Bulk heterojunction organic solar cells fabricated using low-band-gap semiconducting polymers.

Semiconducting copolymers composed of 10-(2'-hexylphenothiazine) (PTZ), 9,9-dioctyl-dithienylfluorene (DTF8), {(2E,2'E)-3,3'-[2,5-bis(octyloxy)-1,4-phenylene]-bis[2-(thiophen-2-yl)acrylonitrile]} (OPTAN), and benzo-[1,2,5]-thiadiazole (BT) units, i.e., poly(PTZ-co-OPTAN-co-BT) and poly(DTF8-co-OPTAN-co-BT), were synthesized through Pd(0)-catalyzed Suzuki coupling with appropriate control of the monomer ratio. The optical band gap energies of the polymers were in the range of 1.95-1.77 eV. The energy levels of the highest occupied molecular orbitals and the lowest unoccupied molecular orbitals of the copolymers were determined via cyclic voltammetry and the optical band gap energies. Photovoltaic devices were fabricated using the polymers as p-type donors and [6,6]-phenyl C61-butyric acid methyl ester (PC60BM) or [6,6]-phenyl C71-butyric acid methyl ester (PC70BM) as electron acceptors.

Pure red phosphorescent organic light-emitting diodes made of iridium(III) complex with thiophene-quinoline ligand.

A cyclometalated iridium(II) complex, bis(2-thiophen-2-yl-quinolinato)(acetoacetonate)iridium(II) [(tq)2Ir(III)(acac)] was synthesized for use in phosphorescent organic light-emitting diodes. The photophysical and electrochemical properties of the iridium(Ill) complex were characterized by UV-visible absorption, photoluminescence, and cyclic voltammetry. The maximum UV-visible absorption of (tq)2Ir(acac) was observed at 289 nm. (Tq)2Ir(acac) in dichloromethane showed its maximum photoluminescence (PL) emission at 629 nm. The optical band gap energy of (tq)2Ir(III)(acac) was measured to be 2.11 eV, and the HOMO energy level of (tq)2Ir(Ill)(acac) was calculated to be -5.08 eV. The T1 state of (tq)2Ir(lll)(acac), calculated from the PL emission maximum (2.01 eV), was well matched with the T1 level of CBP (2.6 eV). The phosphorescent organic light-emitting diode with a configuration of ITO/PEDOT:PSS/alpha-NPD/TCTA/CBP:(tq)2Ir(II)(acac)(8 wt%)/BCP/Alq3/LiF/Al was fabricated and characterized. Light emission from the device was observed at a low turn-on voltage of 4.3 V. The device showed a maximum brightness of 24,000 cd/m2 at 16.3 V and an external quantum efficiency of 11.1% with a Commission Internationale de l'Eclairage (CIE) coordinate of (0.690, 0.310).

High open circuit voltage organic photovoltaic cells fabricated using 9,9'-bifluorenylidene as a non-fullerene type electron acceptor.

We have found that 9,9'BF can be used as an electron acceptor for P3HT-based OPVs while similar devices using 4,4'BP do not show any photovoltaic effect. This can be related to the respective aromaticity and antiaromaticity of the reduced forms of 9,9'BF or 4,4'BP. The OPV device fabricated using P3HT and 9,9'BF exhibited a PCE of 2.28% with a V(oc) of 1.07 V, a J(sc) of 5.04 mA cm(-2), and a FF of 0.42.

Ambulatory blood pressure monitoring and blood pressure load in obese children.

BACKGROUND AND OBJECTIVES: This study was aimed at evaluating the significance of blood pressure (BP) load in ambulatory blood pressure monitoring (ABPM) in obese children and adolescents. SUBJECTS AND METHODS: ABPM was conducted for 60 selected patients who had visited Sunlin Hospital between January 2008 and August 2008. Patients were classified into 3 groups; an obese group whose body mass index (BMI) was > the 95th percentile, an overweight group whose BMI was > the 85th percentile but less than the 95th percentile, and a normal group whose BMI was below the 85th percentile. Overall mean BP, day and night BP and BP load were measured by ABPM. RESULTS: Of the 60 patients, twenty-seven children belonged to the obese group, 9 and 24 to the overweight and the normal group, respectively. Among the three groups, the overall average systolic and diastolic BP, daytime diastolic BP, and systolic BP loads in daytime and nighttime were statistically different. Comparing the obese group with the normal group, systolic BP loads in daytime and nighttime in the obese group were significantly higher than those in the normal group. Also, the obese group had more patients whose BP loads were over 25% greater than the normal group while the difference in the number of patients with overall hypertension was not significantly different. CONCLUSION: Assessment of children's BP through assessment of BP load is a more detailed and precise tool than assessment through mean BP using ABPM and BP can be better controlled using measurement of BP load.