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Mass transport of the [Co(bpy)(3)](II/III) redox electrolyte is found to strongly depend on porosity and pore size of mesoporous TiO(2) films. Photocurrent density is improved by nearly two times with increasing the porosity from 0.52 to 0.59 despite 23% decreased dye loading. Optimized nanostructure sensitized with MK-2 dye shows efficiency of 5.5% at 1 sun.

Three new Ir(III) compounds with deep-blue phosphorescence have been synthesized. These molecules have the general formula of Ir(C ^N) 2 (L ^X), where C ^N ¼ 2 0 ,6 0 -difluoro-2,3 0 -bipyridine (dfpypy) and L ^X ¼ ancillary ligand such as 2-picolinate, pic (1), acetylacetonate, acac (2), or dipivaloylmethanoate, dpm (3).The ancillary ligands have been found to significantly destabilize both HOMO and LUMO levels of the Ir(III) complexes, compared to Ir(dfpypy) 3 , without significantly changing the phosphorescence energy.Compounds 1-3 emit bright blue phosphorescence with l max ¼ 440-460 nm and quantum efficiencies of 0.60-0.95 in solution and the solid state. Double-layer electroluminescent devices using compounds 1-3 as the dopant, CDBP (4,4 0 -bis(9-carbazolyl)-2,2 0 -dimethylbiphenyl) as the host/hole transporting layer, and TPBi (1,3,5-tris(N-phenylbenzimidazole-2-yl)benzene) as the electron transport layer have been fabricated. These EL devices show pure blue colour with high efficiency. The EL device of compound 3 at the doping level of 20 wt% shows the best performance with EQE of 10-15% at the brightness of 10-1000 cd m À2 and the maximum current efficiency of 22 cd A À1 .