Fu-You Li

An expanded conjugation photosensitizer with two different adsorbing groups for solar cells

Three novel hemicyanine derivatives bearing different electron donors, 2-[4-N, N-dimethylaminostyryl]-β-naphthothiazolium propylsulfonate (dye 1), 2-[4-N, N-diethylaminostyryl]-β-naphthothiazolium propylsulfonate (dye 2) and 2-[2-hydroxyl-4-N, N-diethylaminostyryl]-β-naphthothiazolium propylsulfonate (dye 3), were designed and synthesized for use in dye-sensitized mesoporous TiO2 solar cells. Their visible light absorption, luminescence emission, electrochemical properties, and photoelectrochemical properties were systematically studied. Upon comparison, dye 3 was found to be the best sensitizer. Experimental data show that introduction of a hydroxyl group can greatly enhance the electron injection efficiency, moreover, this enhancement can greatly override the unfavourable factor originated from the decrease of the adsorption amount of dye 3. Additionally bearing the hydroxyl group, the dye 3 sensitized solar cell gained remarkably high photoelectric conversion yield of 6.3% under illumination of 80.0 mW cm−2 white light from a Xe lamp.

Photoelectric conversion properties of four novel carboxylated hemicyanine dyes on TiO2 electrode

Four hemicyanine derivatives, 2-[4-(N-ethyl-N-carboxyethyl)amino]phenylethenyl-1,3,3-trimethyl-3H-indolium iodide (BIDC1), 2-[4-(N,N-dicarboxyethyl)amino]phenylethenyl-1,3,3-trimethyl-3H-indolium iodide (BIDC2), 2-[4-(N-ethyl-N-carboxyethyl)amino]phenylethenyl-1,1,3-trimethyl-1H-benz[e]indolium iodide (BIDC3) and 2-[4-(N,N-dicarboxyethyl)amino]phenylethenyl-1,1,3-trimethyl-1H-benz[e]indolium iodide (BIDC4), have been synthesized and identified with regard to their structures and electrochemical properties. It is found that the absorption spectra of BIDC3 and BIDC4 are broader than that of BIDC1 and BIDC2 because the former two have one more benzene ring on the electron acceptor side. Upon adsorption on a TiO2 electrode, the absorption spectra of the four BIDC dyes are all broadened forward to both red and blue sides compared with their respective spectra in ethanol solution. BIDC2 (or BIDC4), bearing two carboxyl groups, has about two (or three) times more adsorption and a broader absorption spectrum on TiO2 film compared with BIDC1 (or BIDC3), which consequently leads to a better light-to-electricity conversion property. Among the four hemicyanine dyes, BIDC4 generated the highest photoelectric conversion yield of 4.9%, with a short-circuit photocurrent of 21.4 mA cm−2, an open-circuit voltage of 424 mV, and a fill factor of 0.49 under irradiation with 90.0 mW cm−2 white light from a Xe lamp.

Carbazole-functionalized europium complex and its high-efficiency organic electroluminescent properties

A complex tris(dibenzoylmethanato){1-ethyl-2-(N-ethyl-carbazole-yl-4) imidazo[4,5-f]1,10phenanthroline} europium(III) [Eu(DBM)3phencarz] functionalized by a hole-transport group carbazole was synthesized. Devices using this complex as emitter showed greatly enhanced performance benefited from the increased hole-transport properties and efficient energy transfer from carbazole to the central ions. A 58-nm-single-layer device gave a brightness of 20 cd/m2 at 15 V. The highest power efficiency of 2.7 lm/W at 5 V and 0.5 cd/m2 and the luminance exceeding 2000 cd/m2 at 20 V was obtained from a device with the configuration of ITO/TPD(20 nm)/Eu(DBM)3phencarz(40 nm)/BCP(20 nm)/AlQ(40 nm)/Mg0.9Ag0.1(200 nm)/Ag(80 nm).

Bright red light-emitting electroluminescence devices based on a functionalized europium complex

The complex tris(dibenzoylmethanato)(1-ethyl-2-(4′-carbazole-9-yl)phenyl imidazo[4,5-f]1,10- phenanthroline) europium (III), Eu(DBM)3(CPIP), was newly synthesized. Devices using this complex as emitter showed greatly enhanced performance benefiting from the improved hole-transporting properties of the complex and good stability. A double-layer device with the configuration of ITO/TPD(50 nm)/Eu(DBM)3(CPIP)(60 nm)/Mg0.9Ag0.1(200 nm)/Ag(80 nm) exhibited Eu3+ based pure red emission with a brightness of 537 cd m−2 at 13 V and the power efficiency of 0.089 lm W−1 at 6 V, 33 cd m−2. A triple-layer device with the configuration of ITO/TPD(40 nm)/Eu(DBM)3(CPIP)(30 nm)/Eu(DBM)3 Bath(50 nm)/Mg0.9Ag0.1 (200 nm)/Ag (80 nm) also emitted pure red light with a highest brightness of 1050 cd m−2 at 16 V and the highest power efficiency of 0.50 lm W−1 at 8 V, 8 cd m−2. The highest brightness 1460 cd m−2 at 14 V was obtained from a four-layer device with the configuration of ITO/TPD(40 nm)/Eu(DBM)3(CPIP)(40 nm)/BCP(20 nm)/AlQ(10 nm)/Mg0.9Ag0.1(200 nm)/Ag(80 nm) and the highest power efficiency of 0.54 lm W−1 at 7 V, 56 cd m−2.

High-performance blue electroluminescent devices based on 2-(4-biphenylyl)-5-(4-carbazole-9-yl)phenyl-1,3,4-oxadiazole.

An electron transporting moiety (1,3,4-oxadiazole) and a hole transporting moiety (carbazole) were combined to create 2-(4-biphenylyl)-5-(4-carbazole-9-yl)phenyl-1,3,4-oxadiazole (CzOxa), a three layer device with a configuration of ITO/TPD(50 nm)/CzOxa(40 nm)/AlQ(40 nm)/Mg0.9Ag0.1(200 nm)/Ag(80 nm) which exhibited a blue emission peak at approximately 470 nm (x = 0.14, y = 0.19) with a maximum luminance of 26,200 cd m(-2) at a drive voltage of 15 V and a maximum luminous efficiency of 2.25 lm W(-1).

Green exciplex emission from a bilayer light-emitting diode containing a rare earth ternary complex

Abstract A bilayer organic light-emitting diode using a blue-fluorescent yttrium complex, tris(1-phenyl-3-methyl-4-isobutyryl-5-pyrazolone)-(2,2 ′ -dipyridyl) yttrium [Y(PMIP) 3 (Bipy)] (YPB) as an emitting material and poly( N -vinylcarbazole) (PVK) as a hole-transporting material emitted bright green light instead of blue light. It was attributed to the exciplex formation at the solid interface between the PVK and YPB layers, which was demonstrated by the measurement of the absorption, photoluminescence (PL) and photoluminescence excitation (PLE) spectra of the mixture of PVK and YPB (molar ratio 1:1). The device exhibited a maximum luminance of 177 cd/m 2 and a peak power efficiency of 0.02 lm/W.

Photoluminescence and electroluminescence of the exciplex formed between a terbium ternary complex and N,N′-diphenyl-N,N′-bis(3-methylphenyl)-1,1′-diphenyl-4,4′-diamine

We demonstrate the photoluminescence (PL) and electroluminescence (EL) of the exciplex formed between a terbium complex tris-(1-phenyl-3-methyl-4-isobutyryl-5-pyrazolone)-1,10-phenanthroline-terbium Tb(PMIP)3(Phen) and the hole-transporting material N,N′-diphenyl-N,N′-bis(3-methylphenyl)-1,1′-diphenyl-4,4′-diamine (TPD). Experimental results show that a new emission peaking at 540 nm from their 1 : 1 mixture and the electroluminescence from the double layer device (ITO/TPD/Tb(PMIP)3(Phen)/Mg0.9Ag0.1) can be assigned to the exciplex formed between the excited state of TPD and the ground state of the terbium complex. By suppressing the formation of the exciplex by changing the carrier combination zone, pure green light from the central terbium ion with highest brightness 250 cd m−2 at 15 V, power efficiency of 0.31 lm W−1 and turn-on voltage as low as 3 V can be obtained from a device of ITO/TPD(10 nm)/Tb(PMIP)3(Phen)(80 nm)/BCP(20 nm)/Mg0.9Ag0.1. By doping TPD into the emitting layer, which facilitates the exciplex formation, bright yellow emission with highest brightness 1180 cd m−2 at 17 V was obtained from a device of ITO/TPD(20 nm)/Tb(PMIP)3(Phen) : TPD(2 : 1)(50 nm)/Tb(PMIP)3(Phen)(20 nm)/AlQ(30 nm)/Mg0.9Ag0.1.

Structure and photoelectrochemical properties of ruthenium(II) polypyridyl complexes as sensitizers for nanocrystalline TiO2 electrodes

The relationship between the structures and photoelectrochemical properties of two dyes, cis-dithiocyanato-N,N′-bis(4,4′-dicarboxyl-2,2′-bipyridyl) Ru(II) and cis-dithiocyanato-(4,4′-dicarboxyl-2,2′-bipyridyl)-(4,4′-di((N,N′-methylphenylamino)methylene)-2,2′-bipyridyl) Ru(II), was examined and compared under the same conditions. Data show that the photophysical properties (including molar extinction coefficients e and excited-state lifetimes) and photoelectrochemical properties (including short-circuit photocurrent, open-circuit photovoltage, incident monochromatic photon to current conversion efficiency, overall energy conversion yield (η) and transient photocurrent) were changed greatly only due to an acceptor replaced by a donor in one of polypyridyl of the Ru(II) complex, suggesting that the molecular design in energy conversion is very sensitive.

Chain-length dependence of photoelectric conversion from a porphyrin monolayer modified electrode

The photoelectrochemistry of a series of porphyrins containing an alkyl chain terminated with imidazolyl, is described. Indium–tin oxide electrodes deposited with porphyrins using the Langmuir–Blodgett (LB) technique exhibit high photocurrent values under ambient condition. Action spectra of the photocurrent generation are coincident with the absorption of the LB film-modified electrodes, indicating that the dye aggregates in the LB film are responsible for the photocurrent. The bias voltages that may influence the photocurrent have also been investigated. The photocurrents varied with the side chain length; the compound with a longer chain but not with the shortest chain generated the maximum photocurrent. To interpret such a special case, a possible mechanism is suggested. 2002 Elsevier Science B.V. All rights reserved.

Crystal structure of MSIA and photochromism of Eu3+–MSIA–phen complex

Abstract The title compound N,N-bis(N-methylenesuccimido) β-alanine (MSIA) was synthesized through the Mannich reaction of succimide with β-alanine in the formaldehyde solution. The structure of MSIA was determined by single crystal X-ray diffraction. The molecule has two five-membered rings with a dihedral angle of 74.45° instead of 180° in the same plane. The chain of β-alanine chooses the serrated conformation rather than linear one. Its Eu3+ complex with 1,10-phenanthroline(phen) has good photochromism in aqueous media.