Charge transport characteristics of dye-sensitized TiO2 nanorods with different aspect ratios

Abstract

Nanocrystalline TiO2 spherical particle (NP) with a dimension of 5 × 5.5 nm and several nanorods (NR) with different aspect ratios (diameter × length: 5 × 8.5, 4 × 15, 4 × 18 and 3.5 × 22 nm) were selectively synthesized by a solvothermal process combined with non-hydrolytic sol-gel reaction. With varying the molar ratio of TTIP to oleic acid from 1:1 to 1:16, the NRs in the pure anatase phase were elongated to the c-axis direction. The prepared NP and NRs were applied for the formation of nanoporous TiO2 layers in dye-sensitized solar cell (DSSC). Among them, NR2 (TiO2 nanorod with 4 × 15 nm) exhibited the highest cell performance: Its photovoltaic conversion efficiency (η) of 6.07%, with Jsc of 13.473 mA/cm2, Voc of 0.640 V, and FF of 70.32%, was 1.44 times that of NP with a size of 5 × 5.5 nm. It was observed from the transient photoelectron spectroscopy and the incident photon to current conversion efficiency (IPCE) spectra that the TiO2 films derived from NR2 demonstrate the longest electron diffusion length (Le) and the highest external quantum efficiency (EQE).