Yasuko Hirayama

Solid-State Dye-Sensitized Solar Cells Using Poly[2-methoxy-5-(2-ethylhexyloxy)-1,4-phenylene-vinylene] as a Hole-Transporting Material

Solid-state dye-sensitized solar cells (DSSCs), consisting of poly[2-methoxy-5-(2-ethylhexyloxy)-1,4-phenylene-vinylene] (MEHPPV) as a hole-transporting material, an indium tin oxide (ITO) electrode, and a titanium dioxide (TiO2) electrode, were studied with respect to the factors affecting their properties. The morphology of TiO2 electrodes, which was controlled by changing preparation conditions, affected the performance of solid-state DSSCs, and cells with a TiO2 electrode having a smooth surface showed better properties. The carrier transportation between the TiO2 layer and the MEHPPV layer was one of the most important factors that determined the overall efficiency of the solar cells. This carrier transportation process was improved by the addition of an interlayer consisting of potassium iodide (KI) and iodine (I2). In addition to improving the carrier transportation, this KI/I2 blend interlayer also improved the pore filling of the solid-state DSSC. By controlling these parameters, a solid-state DSSC was obtained, with a short-circuit current density of about 1.51 mA/cm2, an open circuit voltage of about 0.65 V, a fill factor of about 0.5, and an energy conversion efficiency of about 0.51%.

Multilayer green polymer light emitting diodes with improved efficiency and lifetime

We report on green polymer light emitting diodes with improved efficiency and lifetime using a cross-linked hole transporting layer in this study. The poly[(9,9-dioctylfluorene)-alt-(triphenylamine)], which was used as a hole transporting material, was cross-linked by UV irradiation. The emitting layer of a green copolymer, poly[(9,9-dioctylfluorene)-co-(benzodiathiazole)], was spin coated from its solution on the top of the cross-linked hole transporting layer to prepare a multilayer device. By introducing the cross-linked hole transporting layer, the maximum luminance, efficiency, external quantum efficiency, and, especially, the lifetime of the multilayer green device were greatly increased compared with those of a single layer device. These were supposed to be caused by an improvement of carrier injection balance in the emitting layer, a decrease in the reduction-oxidation degradation of the emitting material, and fewer impurities entering the emitting layer due to the function of the cross-linked hol...