[Organic solar cell based on alkylthiol/Au self-assembly film as buffer layer].

The interface modification between the organic active layer and the inorganic electrode affects the performance of organic solar cell (OSC). A buffer layer of alkylthiol (ethanethiol, hexanethiol, dodecanethiol)/Au self-assembly layer was introduced into OSC to substitute Poly(3,4-ethylenedioxythiophene) : poly(styrene sulfonate) (PEDOT : PSS) layer, in order to improve the organic/inorganic interface. We fabricated devices with structure of "ITO/Au (annealed Au film of 2 nm)-thiol self assembly layer/poly(3-hexylthiophene) : 1-(3-methoxycarbonyl) -propyl-1-phenyl-(6,6)C61(P3HT : PCBM) /LiF/Al". After alkanethiol self-assembling, the alkanethiol prevented exciton quenching owe to direct contact between the Au NPs and the active layer. We studied the impact of alkanethiol with different chain length on device performance. With? the? growth? of? the? alkyl chain, the coverage of the thiol on Au NPs got better, and the device performance become better. In the OSC with dodecane-thiol/Au (2 nm Au film annealed) self-assembly film, the short-circuit current increases from 5.19 mA x cm(-2) to 6.24 mA x cm(-2).

[All wavelength picosecond fluorescent anisotropy of aligned MEH-PPV/PVP electrospun fibers].

Electrospinning is a simple and effect technology which can produce continuous nanofibers. We get aligned electrospun nanofibers successfully by using parallel electrodes. We report our studies on transient fluorescence of aligned electrospun fibers. The fibers are excited and their fluorescences are observed both at axial and radial polarization. Steady-state PL spectra shows radial emission blue-shift more than axial! emission, due to weakened aggregation of molecular chains in radial direction. At all emission wavelength, radial emission excitons migrate faster than axial emission excitons.

[Optimization of optical parametric amplification on femtosecond fluorescence spectra by referring to cone emission].

Femtosecond time-resolved fluorescence spectra technique based on non-collinear optical parametric amplification is a new method for ultrafast spectroscopy research In the present report, the authors discuss the dynamic range for amplifying fluorescence. The supercontinuum seed can be amplified linearly to its transient intensity. Due to large amplification ratio up to 10(7), small instability in pump pulse energy produces large fluctuation in final output amplitude. Here the authors introduce a method using cone emission as reference to overcome this difficulty. The results show significant improvement in fluorescence dynamics curve.

[Enhanced V(oc) in photovoltaic cell by electrodeposited polythiophene thin film].

Poly(3-hexylthiophene) (P3HT) thin films were electrochemically deposited directly on indium tin oxide (ITO)/poly (3,4-ethylenedioxythiophene)-poly(styrenesulfonate) (PEDOT : PSS) substrates. Its optical absorption peak is located at about 410 nm and tailing to 610 nm, corresponding to 2.04 eV of bandgap. Its highest occupied molecular orbital (HOMO) energy is -5.21 eV, while the HOMO energy of the chemically synthesized P3HT is -5.02 eV. The lower HOMO energy of the electrodeposited P3HT may be attributed to the enhancement of regularity. The morphology of the P3HT thin film characterized by atomic force microscopy (AFM) indicates that the molecules contact firmly. The cyclic voltammetry results show that its electrochemical property is stable. The authors prepared photovoltaic cell with the P3HT and [6,6]-phenyl-C61-butyric acid methyl ester (PCBM) as the active layer. Because of the lower HOMO of the electrodeposited P3HT, the open circuit voltage (V(oc)) of the device is up to 0.76 V, indicating a new way to enhance the V(oc) of the organic photovoltaic cells.

[Improvement of the power conversion efficiency in organic solar cells].

Energy is most important issue in the world now because the chemical energy (oil, natural gas, coal et al) is on the edge of depleting. Many Countries are now paying attention to the use of sun power. Photovoltaic device is the most important way to make use of sun energy. Organic solar cell is one promising kind of photovoltaic device, though it's low power conversion efficiency hampers its commercialization. This paper briefly reviewed two ways to improve the power conversion efficiency of organic solar cells and pointed out the unsolved problems.

The improvement of bulk-heterojunction order in polymer photovoltaic device.

The blend morphology and vertical arrangement are critical to the performance of organic bulk-heterojunction photovoltaic devices. In the present paper, the authors proposed a new annealing method that controls the blend morphology and vertical arrangement of two materials by means of simultaneously applying external electrical field and violet irradiation on the active layer of poly(3-hexylthiophene) (P3HT) and [6,6]-phenyl C61-butyric acid methyl ester (PCBM) during annealing process. By using this annealing method, the power conversion efficiency increased by 36%, which was caused by vertical phased-separated blend of crystalline P3HT and PCBM and better charge extraction of electrodes. X-ray photoelectron spectroscopy (XPS) was measured to prove more fullerene derivatives at the organic/cathode interfaces by using this annealing method. The X-ray diffraction (XRD) analysis and UV-Vis absorption spectrum analysis also revealed more ordered polymer crystallization.

Widening of Long-range femtosecond laser filaments in turbulent air.

The influence of air turbulence on the long-range filamentation of femtosecond laser pulses has been numerically investigated. Simulations are performed for different parameters of air turbulence and laser pulses. Simulation results indicate that the diameter of filaments formed by free propagated fs laser pulse can be widened to mm level under air turbulence. However, the widening effect can be suppressed if the propagating distance before the on-set position of filamentation becomes shorter. The reduction of non-linear focal length can be realized by pre-focusing of the laser pulse or increasing of the laser intensity. The effect of the inner scale of air turbulence on the filamentation has also been studied.

[Study of photochemically converted PPV films].

The authors present photoluminescence (PL) and Raman spectra of PPV converted in vacuum by ultraviolet(UV) irradiation which indicate partial conjugation similar to thermally converted poly(p-phenylene vinylene) (PPV). The authors have fabricated OLEDs based on photo-converted PPV. Though the electroluminescence (EL) spectra are poor, doped PPV-based OLED devices are achieved.

[High contrast organic light-emitting diodes using pb-LiF as cathode].

A metal-insulator complex film made by co-evaporating metal Pb and transparent insulator LiF was tested as a low-reflecting cathode to realize high contrast organic light-emitting diodes (OLED). The optical reflectivity and electrical characteristic of the high contrast OLED were studied as compared with the device based on Al as the cathode. The reflectivity of the Pb-LiF complex cathode is 18% only, about 5 times lower than that of Al cathode. The experimental result shows that the high contrast and the conventional OLEDs are similar in terms of the electroluminescent property.