Deeply Repairing Surface States with Wet Chemistry Methods: Enhanced Performance in TiO2 Nanowire Arrays-Based Optoelectronic Device

One-dimensional (1D) single-crystalline rutile TiO2 nanowire arrays (TiO2 NWAs) have generally been considered superior over TiO2 nanoparticle films for the optoelectronic applications. We discovered that the conventional oxygen annealing method cannot efficiently repair the surface trap states of the TiO2 NWAs that significantly influence the charge diffusion. In this work, we demonstrate a highly effective wet chemistry method to repair the surface states by the successive ionic layer adsorption and reaction (SILAR). The density functional calculations (DFT)-based simulation has been used to explain the physical mechanism of reparation of the surface oxygen vacancies of by CdS or PbS quantum dots (QDs). The analysis results of photoluminescence spectroscopy (PL) and electrochemical analysis conformed the enhanced optoelectronic conversion efficiency. A 20-30% improvement in solar cell performance has been obtained over the PbS or CdS QDs coated dye-sensitized solar cells. The SILAR method for deeply repairing the surface trap states can be extended to the systhesis of other semiconducting nanocrystals and its solar energy conversion applications.