No abstract

A sol-gel method with a modified solvent comprising of three simple steps under low-temperature conditions was used to synthesize mono-disperse rutile TiO 2 nanospheres with dandelion-like hierarchical morphology (DHRS) as a light-scattering layer for dye-sensitized solar cells (DSSC). 1,2-Ethanediol (ED) served as a key retardation agent in the second step at 25 uC to slow the hydrolysis and condensation of the TiCl 4 aqueous solution prepared in the first step at 0 uC; the subsequent nucleation of a rutile type phase occurred homogeneously in the third step at 70 uC to generate the rutile TiO 2 nanospheres with highly uniform sizes. The spherical sizes of DHRS were well controlled with the volume ratios of the EDwater solvent mixture in the second step, for which the DHRS of diameter 650-200 nm were produced from the solvent system containing 5-25% ED. A detailed mechanism is presented to rationalize the formation of nanospheres of uniform size in six steps: 1) hydration and hydrolysis, 2) hydrolysis and retardation, 3) hydrolysis and condensation, 4) homogeneous nucleation, 5) aggregation and growth of rod-like crystals and 6) DHRS formation. The DSSC device with a scattering layer made of DHRS (size ~300 nm) performed comparably to that with a scattering layer made of a commercially available TiO 2 paste, making this nano-material a cost-effective alternative for future DSSC commercialization.

To construct a hybrid titania photoanode containing nanoparticles and nanorods of varied size in a multilayer (ML) configuration for dye-sensitized solar cells, the essence of our ML design is a bilayer system with additional layers of nanorods of well-controlled size inserted between the transparent and the scattering layers to enhance the light-harvesting capability for photosensitizers with small absorptivity, such as Z907. We measured charge-extraction and intensity-modulated photoelectric spectra to show the advantages of one-dimensional nanorods with an improved electron-transport property and an upward shift of the potential band edge; a favorable ML configuration was constructed to have a cascade potential feature for feasible electron transport from long nanorods, to normal nanorods, to small nanoparticles. On the basis of the ML system reported herein, we demonstrate how the performance of a Z907 device is improved to attain η ∼10%, which is a milestone for its future commercialization.

Oxasmaragdyrin boron complexes were prepared and applied in DSSCs. The HOMO-LUMO energy gap analyses and theoretical calculations revealed that these expanded porphyrins are ideal sensitizers for DSSCs. A device containing oxasmaragdyrin-BF2 as the sensitizer achieves an energy conversion efficiency of 5.7%.