Suppress the Charge Recombination in Quantum Dot Sensitized Solar Cells by Construct the Al–treated TiO2/TiO2 NRAs Heterojunctions

There are many paths of recombination at the TiO2/CdS/electrolyte interface. It is important to reduce the recombination rate of charges to improve the photoelectric properties of quantum dot sensitized solar cells (QDSCs). In this paper, the TiO2 nanowire arrays (TiO2 NRAs) has been modified with Al-treated TiO2 layer by sol-gel method to construct the Al-treated TiO2/TiO2 NRAs heterojunctions. The analysis results reveal that the Fermi level of the TiO2 has changed after being modified by Al-treated TiO2 layer, which could form the interface electric field. The SPV, TPV and the TPC are applied to analyze the mechanism of photogenerated charge recombination. Due to the interface electric field, the SPV indicates that the separation efficiency of charge is improved; the TPV shows that the recombination of the photogenerated electrons with holes would be suppressed; and the TPC illustrates that the recombination of the photogenerated electrons with holes and electrolyte is reduced. And, the lifetime of the photo-generated electrons is prolonged. Consequently, the QDSCs based on TiO2 NRAs photoelectrodes modified by the Al-treated TiO2 layer exhibit a maximal solar energy conversion efficiency of 2.58 %, which is 45 % higher than that of the TiO2 NRAs photoelectrode. Finally, our method of modifying photoanode exhibits a route to restrain the charge recombination and prolong the lifetime of photo-generated electrons, which shows a tremendous potential for the photoelectrochemical fields.