Search

We examine experimentally and computationally the nature of substitution of perylene in polycrystalline solid alkane matrices (Shpol’skii systems). The technique of low temperature excitation-emission matrix spectroscopy is used to determine all substitution sites in alkane matrices from hexane to decane. A theoretical method from the group of Jortner [Shalev et al., J. Chem. Phys. 95, 3147 (1991)], which was extended and applied by us to this problem in the past [Wallenborn et al., J. Chem. Phys. 112, 1995 (2000)], allows one to separate the perylene sites in all alkanes into normal and defective sites. Normal sites are obtained by direct substitution of two alkane molecules by a perylene molecule, while defective sites are derived from normal sites by eliminating one of the four nearest neighbors of perylene in the lattice planes parallel to the chromophore. We discuss the strengths and limitations of the present theoretical treatment, which can serve as a valuable supplement and guide to line-narrowing...

The use of cyanine dyes in thin-film heterojunction photovoltaic devices is investigated. It is demonstrated that a carbocyanine dye acts as donor in conjunction with buckminsterfullerene (C60). Due to its high electron affinity, the cyanine can also act as acceptor when using copoly(dicyano-phenylvinylene-triphenylamine) as donor. H and J aggregates of the cyanine dye play a determining role both in the photocurrent spectrum and in the open circuit voltage. Open-circuit voltages ranging from 0.25 to 1.28 V are obtained for devices using the cyanine as donor and acceptor, respectively. When the cyanine layer is sandwiched between the polymer donor and the C60 acceptor, incident photon to current conversion efficiencies greater than 10% are observed. The possibility of using cyanine dyes at the same time as donors and acceptors is a promising strategy to improve conversion efficiency.

Ultrafast carrier dynamics of ZnSe nanowires grown under different growth conditions have been studied. Transient absorption measurements reveal the dependence of the competing effects of state filling and photoinduced absorption on the probed energy states. The relaxation of the photogenerated carriers occupying defect states in the stoichiometric and Se-rich samples are single exponentials with time constants of 3-4 ps. State filling is the main contribution for probe energies below 1.85 eV in the Zn-rich grown sample. This ultrafast carrier dynamics study provides an important insight into the role that intrinsic point defects play in the observed photoluminescence from ZnSe nanowires. © 2007 American Institute of Physics. 91 24 Cited By :23

In view of promising full-solar-spectrum photovoltaic systems based on Inx Ga1-x N ternary alloys, femtosecond time-resolved study in ultrathin epilayers was employed in order to extract the fundamental properties of material. Two different thicknesses of epilayers were employed with relative high indium mole fractions. State filling effect at various probing energy states has been observed for both epilayers. Saturation of state filling as well as enhanced photoinduced absorption occurred at higher probing wavelengths. Furthermore, coherent acoustic phonon oscillations were also observed for both ultrathin epilayers with a thickness dependent oscillation frequency. Finally, absorption band edge of these alloys has been determined. © 2006 American Institute of Physics. 89 24 Cited By :1