A P-type icosahedral quasicrystal is formed in Au-Al-Yb alloy of which 6-dimensional lattice parameter a 6D = 7.448 Å. The composition of the quasicrystal was analyzed to be Au 51 Al 34 Yb 15 . This quasicrystal is formed in as-cast alloys, and is regarded as metastable because of decomposition into other crystalline phases by annealing at 700 ºC. Among Tsai-type quasicrystals, this quasicrystal is situated just between Zn-Sc group with smaller a 6D and larger Cd-Yb group. Intermediate valence of Yb recently observed in this quasicrystal may be due to this unique situation, namely smaller major component Au-Al than in Cd-Yb.The predominant phase in the annealed specimen is a 1/1 cubic approximant with lattice parameter a = 14.500 Å belonging to the space group Im ! 3. This phase is stable at the composition Au 51 Al 35 Yb 14 at 700 ºC. Rietveld structural analysis indicated that the crystal structure is understood as periodic arrangement of Tsai-type clusters each
We investigate different parameters influencing the occurrence of s-shaped current voltage (j-V) characteristics in planar heterojunction organic solar cells. It is shown how substrate modification, purity of the active organic material as well as variation of the top contact can affect the shape of the j-V curves. The studies are performed on vacuum-evaporated planar heterojunction solar cells with diindenoperylene (DIP) as electron donor and fullerene C 60 as acceptor. The focus is on the fill factor and forward current being the most direct indicators for s-shapes in j-V curves. We find that the main effect of substrate heating during film growth can be assigned to changes in energy barriers rather than to the modification of morphology and crystallinity, which is also influenced by elevated substrate temperatures. The decisive role of the barrier height between the anode work function and the HOMO (i.e., highest occupied molecular orbital) level of the donor is approved by comparing hole-injection layers with different work functions. By using donor materials of different purity we find a correlation between charge carrier mobilities and fill factors. Finally, it is demonstrated that an exciton blocking interlayer is essential to get high fill factors when aluminum is used as top contact, but is dispensable for samarium as cathode material. This finding can be ascribed to the protective effect of the interlayer from aluminum diffusion into the active semiconductor rather than to its role as exciton diffusion barrier. V
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