Zinc-doping in TiO2 films to enhance electron transport in dye-sensitized solar cells under low-intensity illumination.

A nanocrystalline TiO(2) film with highly dispersed Zn-doping shows its capability for efficient electron transport in dye-sensitized solar cells (DSSCs). The Zn-doping is conducted via Zn(2+) introduction into a layered titanate followed by hydrothermal treatment and calcination. The Zn-doped films exhibit an elevated electron Fermi level, which may enhance band bending to lower the density of empty trap states. Because of this Zn-doping, the consequent DSSCs can alleviate the decay of light-to-electric energy conversion efficiency due to light intensity reduction. Intensity-modulated spectroscopic analysis reveals that enhanced transport of photogenerated electrons as a result of the trap density minimization is responsible for the high cell performance under low-intensity illumination. A Zn-doping content of ca. 0.4 at% Zn/Ti can enhance the light conversion efficiency by 23% at a solar light intensity as low as 11 mW cm(-2). This technique can significantly extend the indoor application of DSSCs.