Significant influence of TiO 2 photoelectrode morphology on the energy conversion efficiency of N719 dye-sensitized solar cell

Abstract

Since Grätzel’s group reported an overall efficiency of 10% for dye-sensitized solar cell using cis-di(thiocyanato)bis(2,2′-bipyridyl-4,4′-dicarboxylate)ruthenium(II), many other institutions have tried to reproduce it. However, no other institutions have, so far, reported such a high efficiency. In order to develop high efficiency dye-sensitized solar cells, the tuning of TiO 2 photoelectrode morphology towards optimization of solar energy conversion efficiency has been investigated. TiO 2 photoelectrodes with six different structures, with layers of nanoparticles, light-scattering particles, and mixture of nanoparticles and light-scattering particles on the conducting glass at a desirable sequence and thickness, were designed and investigated. The profiles of photocurrent action spectra were compared in terms of light scattering and the suppression of light loss due to the back-scattering of large particles near the conducting glass. The data show that the multilayer structure is superior to the mono- and double-layer structure, with ∼85% of incident monochromatic photon-to-electron conversion efficiency (IPCE) below 620 nm and ∼45% of IPCE at 700 nm. The solar-to-electric energy conversion efficiency of N719 dye-sensitized solar cell has been improved significantly from 7.6 to 9.8% by tuning the film structure from monolayer to multilayer. The best efficiency of 10.2% under illumination of simulated AM1.5 solar light (100 mW cm −2) was attained with a multilayer structure using an anti-reflection film on the cell surface.