Fabrication of a multi-scale nanostructure of TiO2 for application in dye-sensitized solar cells

We propose a highly ordered multi-scale nanostructure of TiO2 for applications as an anode in dye-sensitized solar cells (DSSCs). The structure is composed of a TiO2 blocking layer, a TiO2 inverse opal main body, regularly arranged transport channels between contacting spherical voids of the TiO2 inverse opal, and TiO2 nanoparticles coated on the spherical surfaces of the voids. The ordered and continuous backbone of the inverse opal serves as the fast electron transport pathways while the regularly arranged transport channels enable easy transport of dye and electrolyte within the structure. A multi-cycle procedure was developed to enable fabrication of thick inverse opals and easy adjustment of the inverse opal thickness. An example structure was constructed, involving a blocking layer of 90 nm thickness, an inverse opal of 100 nm voids, transport channels of 30-50 nm openings, and nanoparticles 10-15 nm in size. An open-circuit voltage decay investigation showed a significant improvement in electron lifetime for the proposed multi-scale TiO2 nanostructure based DSSC than that of a TiO2 nanoparticle film based DSSC, revealing the superior electron recombination characteristic offered by the proposed TiO2 nanostructure. The conversion efficiency of the DSSC assembled from such an anode structure can reach 4% with a short-circuit current density (J(sc)) of 8.7 mA cm(-2) and open-circuit potential (V-oc) of 0.76 V under AM 1.5 (100 mW cm(-2)) illumination.