The effects of thermal annealing before and after Al deposition on poly͑3-hexylthiophene͒ ͑P3HT͒ / ͓6,6͔-phenyl-C 61 butyric acid methyl ester ͑PCBM͒ blend solar cells were investigated by current density-voltage measurements and x-ray photoelectron spectroscopy ͑XPS͒. Compared to the preannealed device, the postannealed device exhibited enhanced open-circuit voltage ͑V OC ͒, which is ascribed to the decrease in the reverse saturation current density J 0 . The XPS measurements demonstrated that P3HT is dominant at the Al interface in the preannealed device while PCBM is instead dominant in the postannealed device. This surface-segregated PCBM formed in the postannealed device can serve as a hole-blocking layer at the Al interface to reduce J 0 , and therefore improve V OC .

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237, JapanSeveral aluminas were synthesized from aluminium isopropoxide using some organic complexing agents as solvents. The difference in t h e properties, especially specific surface area, of the aluminas obtained was investigated. The thermal behaviour of t h e aluminas depended on the complexing abilities of the solvents used. The transmission electron microscopic studies confirmed that size and shape of t h e gel particles were controlled by t h e complexing agents.

Solution-processed organic thin-film solar cells with triple-layered structures were fabricated by combining a holetransporting layer made of poly(3,4-ethylenedioxythiophene):poly(4-styrenesulfonate) (PEDOT:PSS), a light-harvesting layer assembled by layer-by-layer (LbL) deposition of poly(p-phenylenevinylene) (PPV) and PSS, and an electron-transporting layer of fullerene C 60 dispersed in a polystyrene film. The thickness of the light-harvesting layer was precisely designed and controlled on a scale of nanometers by the LbL deposition technique. The efficiency of exciton generation in the PPV/PSS LbL assembly was estimated for various layered structures by optical simulation considering optical interference effects. For the discussion on the efficiency of exciton diffusion, photoluminescence quenching was measured for the LbL assembly with various thicknesses and analyzed using the onedimensional diffusion model. As a result, the exciton lifetime and diffusion constant were evaluated as 0.67 ( 0.02 ns and 8 × 10 -4 cm 2 s -1 , respectively. On the basis of these analyses, the photocurrent generation in the solar cells was quantitatively explained in terms of the layered structure.